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LIBRARY
Michigan State

University

This is to certify that the

thesis entitled

Malaria in Thailand: Trends and Distribution

presented by

Vanawipha Pasandhanatorn

has been accepted towards fulfillment
of the requirements for

Masters._ degree in My—

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MSU le An Aflirmdlve AetlorVEquel Opportunity Inetltwon

MALARIA IN THAILAND: TRENDS AND DISTRIBUTION

BY

Vanawipha Pasandhanatorn

A THESIS

Submitted to
Michigan State University
in partial fulfillment of the requirements

for the degree of

MASTER OF ARTS

Department of Geography

1990

.,
4.9. ",7 l
V aims.

J”. av
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ABSTRACT
MALARIA IN THAILAND: TRENDS AND DISTRIBUTION
BY

Vanawipha Pasandhanatorn

This study focuses on the trends and geographic
patterns of malaria in Thailand. It examines mortality
rates during 1943-1986, morbidity from 1972-1988, and
geographic patterns, 1977-1988.

The findings show steadily downward trends of
mortality rates since 1943 except in 1971, 1973, 1974, and
1981. The significant decline in death rates during 1949-
1970 is generally regarded as a consequence of using DDT,
together with increasing malaria surveillance for early
detection of cases. During the 19503 and 1960s economic
development of the country increased in tandem with with
this steady decline of malaria death during the successful
DDT campaings. Speculation suggests that malaria resurgence
in 1971 was due to the reduction if insecticide use, in
connection with a withdrawal of financial support from the
international community during 1968-1972. The new peak in
1981 was reflected in higher incidence rates and also an
increase in the number of affected geographic areas.
Demographically, the worst afflicted group comprised males
of working-age: 15—24 years. Population most at risk were
migrants moving to live and work in mosquito-infested

transmission areas.

Malaria morbidity appears to fluctuate and is
consistently high with two peaks, a few weeks after
rainfall in June-July, and in December, when temperatures
are 76-83 0F with a relative humidity of 72-78%, that is
when conditions are warmer and more moist. Highest malaria
incidence occurs in three separate geographical regions:
the Southeast, the Northwest, and the South. Most of the
provinces having a high incidence are located near the
border zone with Burma on the West and the South, and with
Kampuchea on the East.

Malaria morbidity in Thailand involves a complex of
ecological, environmental, and economic factors.
Topographic and climatic conditions of the tropical rain
forest contribute, in part, to the indigenous malaria of
the three high incidence areas. Agricultural land—use and
mineral extraction attract migrant populations. Migration
workers, engaged in legal or illegal economic activities,
may work at night when mosquitoes are most active, and they
are therefore exposed to a high risk of infective bites.
International migration resulting from political conflict
among Thailand's neighbors tend to increase the problem of
high malaria incidence. Provinces in the Southeast are
known to have a high level of parasite resistance to drugs.
The malaria problem becomes more difficult to curb due to
increasing mosquito-resistance to insecticides, as well as

community objection to DDT spraying of their houses.

Dedication

For my faithful parents who have given me never-ending

encouragement in my career.

iv

ACKNOWLEDGEMENTS

My gratitude goes to the Steering Committee of
UNDP/World Bank/WHO Special Programme for Research and
Training in Tropical Diseases for awarding me a grant for
graduate study. I am sincerely grateful to Dr. Suban
Panvisavas, Dean of the Faculty of Social Sciences and
Humanities, Mahidol University, Bangkok, for approving my
leave of absence.

My appreciation goes to Dr. J. M. Hunter, advisor and
chairman of my thesis committee, who trained and guided me
in medical geography, and to Drs. G. A. Manson, R. N.
Thomas, J. R. Harman, and J. M. Olson, for their helpful
suggestions and support. Michael Lipsey assisted me with
the computer-generated maps.

My special thanks go to Mrs. Wonwimon and Mr. Samnao
Charittham for providing malaria data needed for completing
this thesis. Mrs. Jean Myers provided warm hospitality

throughout my stay in the United States.

Table of Contents

List of Tables viii
List of Figures ix
Chapter 1: Introduction 1
Statement of the Problem 1
Structure of the Study 3

Chapter 2: Malaria and Its Transmission in South-East 5
Asia Region

Medical Ecology of Malaria and Transmission Cycle 5

Malaria Situation in the South—East Asia Region 13
Causes and Effects of Resurgence 21
Chapter 3: Methods of Analysis and Sources of Data 30

on Malaria in Thailand

Chapter 4: Geographical Profile of Thailand and 35

Malaria Transmission and Control

Physical Environment of Thailand 35
Population and Socioeconomic Conditions 38
Malaria Transmissions and Parasites 4O
Established Malaria Control in Thailand 43

vi

Chapter 5: Results and Discussion

General Trends of Malaria Mortality Rates
Malaria Mortality Rates by Sex and Age Group

Malaria Morbidity Rates:
Malaria Morbidity Trends
Seasonal Climatic Conditions of Malaria

Occurrence

Geographic Patterns of Malaria
Areas of Highest Incidence
iFactors Contributing to High Malaria Rates
Other Susceptible and Prospective

Malarial Areas
Chapter 6: Conclusions and Recommendations
Conclusions
Recommendations

References

Appendices

A 110-

B 116-

vii

46

46

55

62

62

67

73

73

79

91

94

94

100

102

115

118

Table

Table

Table

Table

Table

Table

Table

Table

Table

Table

Table

2.1

5.1

5.2

5.3

5.4

5.5

5.6

5.7

5.8

5.9

A1.

List of Tables

Number of Malaria Cases Reported by WHO 17
Regions (in Thousand), 1972-1984.

Malaria Mortality Rates and Rate of Change, 52
1943-1986 (Rates per 100,000 Population).
Percentage Distribution of the Economic 53
Active Population Aged 11 and Over, by
Industryzl960-1980, and by Residence, 1980.
Malaria Mortality Rates by Sex, 1977-1986 56
(Rates per 100,000 Population).

Percentage of Malaria Mortality Male and 60
Female Combined by Age Group, 1982-1986.
Malaria Morbidity Rates in Thailand, 65
1972-1988 (API Rates per 1,000 Population).
Number of Village Voluntary Malaria 65
Collaborators in Thailand: 1981-1983.

The Average Monthly Malaria Morbidity Rates 70
and Climate Conditions in Thailand: 1985-1988.
Number of Reported Positive Cases of Malaria 72
by Month in Selected Provinces, Thailand:

1987 and 1988.

Result of Spraying Operation 90
Malaria Morbidity in Thailand, 1977-1988. 110

Annual Parasite Incidence Rates by Province.

viii

Table A2.

Table A3.

Table A4.

Selected Provinces Having High Annual 113
Parasite Incidence Rates Over 10 per

1,000 Population.

Number of Immigrants in Selected Provinces, 114
1970-1980.

Number of Immigrants to Provinces Having 115

High Endemic Areas of Malaria

ix

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

List of Figures

Malaria Mortality, Thailand, Five Year
Intervals: 1943-1986.
Annual Malaria Mortality, Thailand:
1965-1986.

Annual Percentage Change in Malaria
Mortality, Thailand: 1965-1986.

Malaria Mortality Rates by Sex, 1977-1986.
Comparison of Malaria Mortality by Age
Group and Year, 1982-1986.
Comparison of Malaria Deaths Between
Children and Working-Age Groups.
Comparison of Malaria Deaths Between
Infant and Middle-Age Groups.
Malaria Morbidity Rates, Thailand:
1972-1988.

Annual Percentage Change in Malaria
Morbidity, Thailand: 1973-1988.

Malaria Incidence Rates and Rainfall.

Malaria Incidence Rates and Mean Temperature.

Malaria Incidence Rates and Relative
Humidity.

Malaria Morbidity in Thailand, 1977-1988

Annual Parasite Incidence Rates, by Province.

54

54

54

57

61

61

61

66

66

71

71

71

75

Figure

Figure

Figure

Figure
Figure

Figure

Bl.

BZ.

BB.

Malaria Morbidity in Thailand, Peak Years 76
(1981,1982) Versus Recent Years (1987,1988).
Annual Parasite Incidence Rates, by Province.
Malaria Morbidity in the Southeast and the 77
South of Thailand, Peak Years (1981,1982)
Versus Recent Years (1987,1988).

Annual Parasite Incidence Rates, by Province.
Malaria Morbidity in the Northwest of 78
Thailand, Peak Years (1981,1982) Versus

Recent Years (1987,1988).

Annual Parasite Incidence Rates, by Province.

Thailand: Physiographic Regions. 116
Vegetation. 117
Provinces in Thailand. 118

xi

Chapter 1

IDEIQQQQELQD

Malaria is a serious infectious disease in most
tropical countries. In the keynote address at the 12th
workshop of the Southeast Asia Medical Information Center,
Ohashi (1984), Coordinator of the Committee on Infectious
Disease, remarked that "Malaria is a severe and frequently
fatal disease that is still prevalent in Southeast Asia in
spite of the anti-malaria activities of respective countries
with malaria, and the World Health Organization". Thailand
has recognized that malaria is a major problem which is
more difficult to control than any other transmissible
disease. There is need not only for measures to improve
public awareness and people's attitudes towards providing
medical care for afflicted individuals, but also for the
expansion of scientific and environmental programs to
control vector and parasite prevalences. Improvements
in both awareness and programs will drastically reduce

malarial death rates in the Thai population.

Statement t P

In 1943 malaria was the leading cause of death in
Thailand, but it quickly dropped over 15 years to the fifth
cause of death in 1958 (Pinichpongse, 1984). It is

hypothesized that this decline was a result of using

dichlorodiphenyl trichloroethane (DDT) spraying. Although
statistics show that malaria had dropped to seventh place
among causes of death in 1984 (Pinichpongse, 1984), many
affected areas are still far from eradicating the disease.
Malaria has reappeared and is still prevalent in many parts
of Thailand. Akhtar and Learmonth (1982) observed that»
even one positive malarial case could eventually give rise
to a great increase in the number of malarial cases. The
global history of malaria control reflects both the
encouraging successes of control measures, and the
discouraging resurgence of the disease (Bruce-Chwatt,
1979, 1985: Wessen, 1986: World Health Organization [WHO],
1986a: Wyler, 1983). Effective control of malaria is the
ultimate goal; however, effective control depends on fully
understanding historical and current trends in malaria
incidence in order to predict possible future occurrences.
Basically, a disease occurs when various intrinsic
factors such as the human host, agent, vector or carrier
and extrinsic factors such as environmental elements
-physica1, biological, socioeconomic, and cultural-
coincide in time and place. Accordingly, medical geography
is concerned with investigating and analyzing geographic
environments which affect human health (Hunter, 1974; Pyle,
1979). A method of disease mapping, which locates the
spatial variations of a particular disease of interest, is

a crucial visual analytic tool. As a case in point, the

use of temporal malarial distribution mapping assists in
identifying risk areas where the disease is clustered,
widespread, or absent. Consequently, analysis of
malaria distribution at the local level, as in provinces,
and predicting of potential localities and time of malaria
occurrence, may aid in initiating immediate control
measures.
The specific objectives of this study are to:

1). Trace the trends of malaria mortality in Thailand
between 1943-1986:

2). Examine the demographic characteristics of
afflicted group.

3) Trace the trends of malaria morbidity between
1972-1988:

4). Examine time occurrence and climatic conditions
that are associated with malaria incidence:

5). Examine geographical patterns of malaria
prevalence at provincial levels and to use this information
to suggest probable areas to concentrate the malaria

control programs.

Structure of the Study

Chapter 2 of this study reviews the general background
of the medical ecology of malaria and its transmission
cycle, including the malaria situation in countries of the

South-East Asia Region (SEAR). Chapter 3 covers methods

and sources of data. Chapter 4 describes the geographical
profile of Thailand and the establishment of malaria
control in the country. Chapter 5 discusses the findings.
Finally, Chapter 6 summarizes the findings and

recommendations.

Chapter 2

Malaria and Its Transmission in South-East Asia Region

This chapter focuses upon a literature review and is
divided into two sections. The first section discusses how
malaria occurs, how the disease is transmitted, and when
and where this disease occurs. The second section
describes the malaria situation in the Indian subcontinent

and Southeast Asia.

ed'c co o o M a T ansmi 'on C cle.

The mechanism of malaria transmission is complicated
due to the three component organisms and a number of
ecological factors involved. Malaria develops when the
Elasmodium parasite is transmitted between people by the
female Anopheles mosquito. In addition to human hosts, the
parasite and vector both require specific ecological
conditions in terms of temperature, relative humidity,
rainfall, and physical landscape for malaria perpetuity.
This study will focus on malaria caused by g. fglgiparum
due to the fact that B. falgipagum is the most common
species found in Thailand. It has also accounted for one
third of the total malaria infections of South-East Asia
Region (WHO, 1988).

The complicated nature of malaria transmission is

partially due to the differences among parasite species

which cause different degrees of infection and symptoms,
and require different diagnosis and treatment. Of the four
Plasmodium species, i.e., P. falciparum, 2. Viva , P.

ovale, and 2. alariae, P. falciparum causes the most

 

morbidity and mortality and also presents the therapeutic
problem of resistance to the drug, Chloroquine (Miller,
1984). Malignant tertian malaria caused by P. falciparum
is confined to the tropics and subtropics. In Africa, it
is responsible for more deaths than any other single cause.

Benign tertian malaria caused by P. vivax, was once common

 

in temperate countries, and is now found only in
subtropics. Quantan malaria, caused by P. malariae, was
eradicated from temperate countries, but is now relatively

uncommon. Malaria caused by P. ovale is rare, with most

 

cases occurring in West Africa (Bruce-Chwatt, 1985).

Malaria life cycles

The life cycles of the four malarial parasites are
similar, with sexual development (sporogony) occurring in
appropriate Anopheles mosquito hosts and asexual
maturation (schizogony) occurring in the human hosts. When
the mosquito vector extracts blood from an infected person,
the parasites grow in the mosquito and increase in number.
Each infectious form of parasite requires a specific
extrinsic phase (maturation period) and specific

temperature before a mosquito carrying the parasite will

become infective toward man (Pampana, 1969). The extrinsic
phase for P. falciparum is 12-16 days at an average
temperature of 73.4 0F (23 oC). The parasite enters it
asexual development when the mosquito inoculates
sporozoites into a person during its blood meal, which is
required for the production and maturation of its eggs.

The sporozoites enter the liver where they grow and divide
into schizonts and form into merozoites for a period of
about one week. Merozoites then break out from the liver,
at which time they become mature schizonts. Schizonts move
into the bloodstream penetrating the red blood cells. The
schizonts burst, destroying the infected red blood cell and
releasing more merozoites into the blood stream to continue

the malaria cycle (Pampana, 1969).

Pat 010 and ia o a

Pyroxysm, a manifested attack of the disease, occurs
when the schizonts spread into the red cells. Symptoms
such as fever, headache, nausea, body pain, and
gastrointestinal upsets, which are similar to those of
influenza or a hangover, may be experienced by the infected
individual. Fever in malaria, typically has three stages.
The first stage begins with a cold fever accompanied by
chill and rigor. This stage lasts between 30 minutes and 2
hours. It is followed by a hot stage where a high fever

with temperatures of 104 oF (40 0C) or more are

experienced. This stage lasts several hours. Finally, a
sweating stage of defervescence accompanied by severe
headache, vomiting, and great thirst begins. The.
temperature of the infected person falls quickly in the
third stage which can last for 2 or more hours. In all
types of malaria, the spleen is almost invariably enlarged.
The severity of pathologic changes and clinical
manifestations in acute malaria is directly proportional to
the percentage of parasite in the red cells. Patients with
acute parasitemia caused by P. falciparum, suffer loss of
red cells and experience anemia. Many suffer coma,
followed by death. About 20 percent of malaria patients
even under good medical care, frequently experience the
final manifestation of cerebral P. falgiparum malaria
(Manson-Bahr and Apted, 1982).

The definitive diagnosis of a person showing symptoms
of malaria is made through examination of a blood smear
from which the percentage of malarial parasite in the blood
can be calculated. The standardized indicator of malaria
morbidity (positive blood film) in a community is defined
by annual parasite incidence (API) rates. API rate is the
proportion of malarial cases detected on an annual basis in
relation to the unit of population in which malaria occurs.
{Hmis is normally standardized to 1,000 population.

Malaria is an acute and chronic disease and may be

fatal if untreated or if treatment is delayed. Because of

resistance of the parasite, an ideal chemoprophylaxis is
not presently available, and a vaccine is still in a
research stage, the effective treatment of malaria requires
prompt diagnosis and early treatment. The most commonly
prescribed drugs are quinine, chloroquine, sulfadoxine-
pyrimethamine (Fansida), and other 4 amino-quinineline.
All parasite malarial species are susceptible to
chloroquine treatment. For prevention, the following are
recommended: avoiding contact with night-biting anopheles,
using bed net, house screening, insecticide, or mosquito
repellents, and taking prophylaxis drug before and after

travelling to the endemic malarious areas.

'ma 0 ' ' e ' a a ans 'ssion

Climatic and topographic features determine the
ecologies and interactions of both human and mosquito
hosts. The three principal environmental factors
influencing malaria transmission and seasonal incidence are
temperature, relative humidity, and rainfall (Pampana,
1969).

Temperature affects the parasite sexual cycle and
additionally affects the frequency with which the
lnosquitoes breed. The ideal mean temperature for malaria
perpetuity ranges from 68 0F to 86 oF (20 °C to 30 0C).
‘This temperature range is desirable for mosquito activity,

breeding, and transmission of parasite. Below a

10

temperature of 59-60 0F (15-16 0C), no species of malaria
parasite can develop within the mosquitoes. The low
temperature limit is 66.2 0F (19 0C) for P. falciparum and
59°F (15 °C) for 2. xiyax. Above 89.6 °F (32 0C) parasite
survival drops sharply (Bruce-Chwatt, 1985: Dutta and Dutt,
1978: Pampana, 1969).

The effect of relative humidity (R.H.) on parasite
development has not been definitively documented. High
relative humidity does, however, affect the life span of
the mosquito and its activity. Relative humidity directly
affects the length of life and activity of the mosquito
vector. Low humidity shortens the life span of the
mosquito. Russell (1952) remarked that where the average
monthly R.H. is lower than 60 percent, there is no malaria
transmission. Rainfall is associated with higher relative

humidity. This allows for greater longevity of Anopheline

 

and intensifies its biting cycle. For instance, A.
minimus, bites at night when relatively lower temperatures
and higher R.H. prevail.

Rainfall does not affect the continuance of the
malaria cycle, but it indirectly influences malaria
transmission through the creation of surface water
collections which serve as mosquito breeding sites. Such
sites are also necessary for larval habitat before they
reach adulthood. The larval stage may last from a week to

several months depending on the species and on various

11

environmental factors. The breeding and biting cycles of
Angphgling are most intense during the rainy season and the
first few weeks which follow this season. Consequently,
the greatest incidence of human malaria occurs during the
latter portion of the rainy season and immediately
afterwards. However, the incidence of malaria cannot
always be related to rainfall patterns in this way. Where
the conditions of high R.H. and ideal temperature are
present year round, such as in the state of Bendal,
Nigeria, an increase in rainfall during July does not
accentuate malaria incidence during the following month.

On the other hand, in Trichy, India, high R.H. accompanied
by ideal temperatures and a large amount of rainfall during
September and October increases malaria incidence during
September and December (Dutta and Dutt, 1978).

Topographic features can also affect malaria
incidence. Malaria breeding sites in the physical
landscape can be found in the form of still pools or swamps
where water may be fresh or salty, pure or contaminated.
Additionally, breeding sites may be associated with gently
or swiftly flowing water. Sites may be in deep shade or
exposed to sunlight (WHO, 1969). The most favorable
breeding sites of mosquitoes are the forest foothill areas.

Malaria occurrence also varies depending on latitude
and altitude. Malaria is usually restricted to areas lying

between 65 0N latitude and 40 oS latitude. Transmission of

12

malaria decreases with increasing altitude and the disease
is usually nonexistent in higher mountain areas. In India,
the coastal plains along the peninsula are healthy areas
(Dutt, Akhtar, and Dutt, 1980), but coastal areas of Papua
New Guinea are high malaria prevalence. Dutta and Dutt
(1978) have proposed that the upper altitudinal limit of
malaria occurs is ranging from 6,000 to 8,000 ft. above
sea-level within 200 latitude of the equator; 3,000 to
5,000 ft. between 30°-4o°, and 1,500 ft. at 50° of the
equator. Thus, the geographic range of tropical and
subtropical zones, which have the potential for year-round
development of malaria parasites and malaria transmission,
create the basis for hyperendemicity.

The other component of the malaria life cycle concerns
humans. Activities of human hosts are often the important
factors that determine the distribution and geographical
range of malaria parasite and vector. The vector may
spread with human assistance. For example A. gambia
crossed from Africa with people probably through ship, to
Brazil in 1930, and resulted in a serious epidemic in that
country (Bruce-Chwatt, 1985). In some countries, there is
periodic migration of populations cross national
boundaries, or migration from rural-to-rural locations and
rural-to-urban locations. The migration of agricultural or
other laborers who are free of disease to hyperendemic

malaria areas puts these people at high risk to malaria.

13

Sometimes they return as malaria carriers to their homeland

(Prothero, 1961, 1983).

Malaria Situation in the South-East Asia Region

This section discusses the history of malaria control
measures and malaria situation of countries in the South-
East Asia Region (SEAR).

Some malaria control, long attempted in many places,
has had only limited success. The most commonly used
malaria control measures include drainage, prophylactic
drugs, larvicides and insecticides. These measures are
most often found being used in various combinations rather
than employed singly. Drainage as a method was first used
to control malaria in ancient Rome and has been in
widespread use in many places even in the twentieth
century. However, it is expensive and rarely gives full
control of the disease where the vector can find other
suitable breeding places such as canals and ditches.
Prevention of malarial illness by taking prophylactic
drugs, such as alkaloid quinine which became available in
1820, has been partially successful. The use of common
oils, i.e., petroleum, which act as larvicides has been
noted since 1793 (Pampana and Russell, 1955). During the
World War I, the British army developed a campaign to rid
areas of mosquito breeding places. Since then, the

emphasis in malaria control has been on reducing mosquito

14

breeding sites, and yet this method has been found less
effective and less economical than to destroy the adult
mosquito.

Focus on adulticide was begun by the U.S. army in Cuba
after the Spanish-American war ended in 1898 (Shuller,
1985). The primary method of control was to fumigate
contaminated houses with smoke, and then to destroy
mosquito larvae. The insecticide dichlorodiphenyl
trichloroethane (DDT), was introduced in 1944. Killing of
adult mosquitoes through the spraying of DDT in dwelling
places has become the most effective and most widely used
method of malaria control. In the U.S. during 1948, more
than 1.36 million tons of DDT was sprayed. The killing of
Anopheles mosquitos aided in the total eradication of the
malaria by 1951 in the U.S. (Shuller, 1985). Similar
success was achieved in many countries in Europe, as
illustrated in the case of Italy. In 1919, there were
303,057 reported cases of malaria in Italy. By 1945, the
number had grown to 411,602 cases. After systematic
spraying with DDT was begun in 1946, the number of reported
cases decreased rapidly and only 12 cases of indigenous
malaria were reported in 1954.

Since the World War II, national and international
organizations have taken action against malaria. Most
malarial countries have extensive malaria control programs,

many assisted through the collaboration of the World Health

15

Organization (WHO), the United Nations Children's Fund
(UNICEF) and the United States Agency for International
Development (USAID). Assistance has focused on technical
guidance, training personnel for malaria work, and
promoting the exchange of knowledge of modern malaria
control methods, also aided with the financial assistance
for actual control operations. From 1955-1969, the WHO
started its malaria campaign for global eradication
primarily based on the use of the cheap and effective,
residual insecticide DDT in combination with other
measures. Many areas where control and eradication
programs were established reported success. While in 1953,
eighty-four million people or 30% of the population who
lived in malarious areas were protected, in 1955,
approximately 60% of the world’s population still lived in
malarial risk areas. During this period, it was estimated
that more than 200 million people suffered annually from
the disease, and about 2 million people died each year
(Shuller, 1985). By 1970, eradication programs had freed
727 million people from the risk of malaria. This number
represented 53% of the population of the original malarial

areas (WHO, 1979).

es nce
Apparently, malaria eradication was so widely

successful that the disease seemed to have been wiped out.

16

However, this has been proven to be the case only in some
developed countries of the temperate zone, but not in many
tropical countries of Africa, Latin America, South and
Southeast Asia, and the Southwest Pacific. By 1970, it had
become clear that malaria eradication had run into severe
difficulties and that the number of infected individuals
had risen again to epidemic proportions. In the mid

1970s, malaria cases reported globally showed great
resurgence compared to the level of the mid 1960s. While a
resurgence of the disease reached a peak in 1976, followed
by a decrease in the numbers of cases, by 1984 the number
of cases reported were nearly equal to those reported in
1974 (see Table 2.1). In some countries, the numbers of
cases reported in the mid 1970s increased 30-40 fold over
1969-1970 levels (WHO, 1978). Since then, emphasis has
shifted from a malaria eradication program to a malaria
control program aimed at the reduction of the incidence of
the disease to a level where it is no longer a major public

health problem (WHO, 1979).

Examples of Malaria Decline and Resurgence

After a period of success in the late 1960s, the
malaria situation began to worsen in every part of the
world, especially in developing countries in the tropical
areas of South and Southeast Asia, Latin America, South

America, and Africa. Those countries continually reported

Table

(in thousands),

17

197

2-1984.

2.1 Number of malaria cases reported by WHO Regions

 

 

 

 

 

 

 

WHO regions 1972 1973 1974 1975 1976 1977 1978
Africa" - - - 4,209 5,514 4,881 7,444
Americasc 284 280 269 357 379 399 469
S/E Asia 1,920 2,694 4,210 6,105 7,304 5,540 4,800
Europe 21 13 8 13 41 119 93
East 855 883 524 429 329 227 162
Mediterranean

W. Pacific 171 203 170 188 211 4,457 3,422

Total 3,251 4,073 5,181 7,092 8,284 10,742 8,946
(excluding Africa) c c

Change 100 125 157 218 255 330 275
(1972 = 100)

Cont’d

WHO regions 1979 1980 1981 1982 1983 1984*
Africa". 5,720 7,146 7,872 5,570 5,631 -
America 6 515 603 630 715 831 914
S/E Asia 3,666 3,706 3,459 2,936 2,529 2,711
Europe 34 38 60 66 71 60
East 125 137 186 309 294 305

Mediterranean
W. Pacific 2,706 3,654 3,450 2,435 1,839 1,300

Total 7,046 8,138 7,785 6,461 5,564 5,289
(excluding Africa)

Change 217 250 239 199 171 163

(1972 = 100)

 

Nope. 1. 1972-1974 from "Malaria Control -a Reoriented
Strategy" by World Health Organization, 1978,
WHQ Chronicle, g2, p. 226.

2. 1975-1984 from "A World Malaria Situation 1984"
by World Health Organization, 1986a World Health
Statisfiss_guarterlx. 32. p- 173-

* Provisional.

a The information provided does not cover the total
population at risk in some instances.

b Mainly clinically diagnosed cases.

c Excluding China.

l8

malaria reappearances. Colombia, with an eradication
program which has been in operation since 1950, showed
decreased rates of malaria incidence and mortality until
1970. However, in recent years the rate has started to
rise again in affected areas in Colombia (Bangufro, 1984).
In Africa, during the 1950s and 19603, malaria control in
the Lowveld areas of South Africa and Swaziland also
reported success, but success was followed by a resurgence
of malaria during the 1970s (Packard, 1986).

Excluding Africa and China, of all global malaria
cases reported by WHO, the South-East Asia Region (SEAR-
including countries on the Indian subcontinent and in
Southeast Asia) has accounted for half, and sometimes more
than 80% of reported cases (Table 2.1).

ngle, where the history of malaria control reflects
the worldwide picture of successful control and then
resurgence, reported greatest number of malaria cases. At
the time of Indian independence in 1947, the estimated
death toll from malaria was eight million yearly. However,
with the implementation of control measures, it was
estimated that 500,000 people were protected from the
disease during 1949. A rapid decrease in morbidity and
mortality was achieved, and by 1965 it was estimated that
there were 100,000 existing cases while no deaths occurred
in that year (Akhtar and Learmonth, 1982; Dutt, Akhtar, and

Dutta, 1980: Hyma and Ramesh, 1980; Learmonth, 1988). But

19

by 1966, the incidence of malaria began to increase and
peaked in 1975-76 with over 5 million cases reported
(Sharma and Mehrotra, 1986). Akhtar and Learmonth (1982)
mapped malaria diffusion in India between 1965 and 1976.

Pakistan has struggled against malaria and named it as
its top health priority in 1961. The eradication program
with DDT succeeded in reducing malaria in rural areas from
an estimated seven million cases in 1961 to 9,500 cases in
1967. The slide positive rate (SPR, the percentage of the
total number of slides examined that were positive for
malaria parasites) determined in surveillance operations
during the same period decreased from 15% to less than
0.01%. However, since 1967, Pakistan's urban areas have
experienced particularly large increases of malaria. By
1972, in Punjab, the most populous and most malarious
province in the country, 20.4% of the population tested
positive for malaria, and epidemic conditions were reached
in many districts. The total estimated number of cases in
that year was 10 million (De Zulueta, 1980). The positive
case rate examined by blood specimens rose from 0.59
percent in 1979 to 2.3 percent in 1984.

Sri Lanka began a major DDT spraying campaign in 1946.
In the first year, DDT spray was successful in decreasing
malaria mortality from 12,587 to 4,562 persons. The
malaria mortality rate declined quickly and reached a low

point of 0.2 per million in 1966 (Brown, 1986). However,

20

by 1975, malaria incidence soared to 600,000 reported
cases. The actual number of cases was estimated to be
substantially higher, perhaps as much as four times
compared to 1963 (Shuller, 1985). The number of positive
cases dropped to 48,000 in 1980, and again increased to
149,000 cases in 1984 (WHO, 1988).

gangladesp reported country—wide malaria prevalence
between 1970-1976 and found that the proportion of positive
slides increased yearly from 0.11 percent in 1970 to 0.84
in 1974, and peaked to 1.07 percent in 1975 (Rosenberg and
Maheswary, 1982). In 1980, positive cases were 68,000 and
dropped to 30,000 in 1985 (WHO, 1988).

Similarly, after an initial period of successful
control using DDT in the late 1960s, other countries in
Southeast Asia were faced with a resurgence of malaria by
the mid 1970s.

gppme noted that its malaria situation worsened in
1976, with the annual parasite incidence (API) increasing
from 0.50 in 1976 to 0.72 per thousand in 1980 and a slide
positive rate (SPR) rising from 1.8 per cent in 1976 to 3.3
percent in 1975 (Harinasuta, Dixon, Warren, and Doberstyn,
1982).

Indonesia found that malaria cases increased from
9,000 in 1965 to 346,000 in 1973 and then decreased to

78,854 in 1979. However, in 1980, the number of cases

increased again, particularly in the central part of Java

21

(Brandling-Bennett, Doberstyn, and Pinichpongse, 1981).
There was an improvement in 1984. The number of cases
detected decreased from 134,000 in 1983 to 86,000 in 1984
(WHO, 1988).

The present situation of global malaria occurrence
(Table 2.1) is such that the number of cases being reported
since 1984 is in line with the pre-resurgence figures of
1974. Nevertheless, the number of present cases reported
has not been reduced to the levels during the eradication

period of the mid 19605.

Causes and Effects of Resurgence

The factors contributing to malaria resurgence are
complicated due to many problems. Budgeting and
administrative difficulties encountered, technical problems
due to the resistance of Anopheles vectors to insecticides
and the parasites resistance to drugs, and population
movement as well as the lack of co-operation of the
population with respect to insecticide spraying are factors

responsible for malaria reoccurrence.

Budgetapy and Administrapive Difficulties

Often insufficient operating funds, lack of material
resources, inflationary rises in the cost of insecticides
and labor affected some of the largest eradication programs

of India, Pakistan, Sri lanka, Indonesia, and Thailand.

22

Financial problems resulted in a decrease in insecticide
usage and coverage areas under the control plan. As a
consequence, there was a failure to interrupt the disease
transmission.

In the case of India, funds from international aid
programs were important in ensuring the flow of imports of
the residual insecticides. The termination of aid for the
program in 1965 severely delayed the flow of supplies in
subsequent years. The lack of supplies resulted in
incomplete coverage of areas under the control plan and, in
turn, a failure to interrupt the transmission of the
disease. The anti-malaria program also suffered from
national budgetary difficulties due to a disproportionate
amount of the national budget being funnelled to defense
expenditures to control Chinese incursions at the northern
boundary of the country. Another portion of the budget,
initially earmarked for malaria control, was redirected to
purchase food imports necessary to offset the effects of
several years of crop failure in the mid-19605 (Chapin and
Wasserstrom 1983; Sharma and Mehrotra, 1986).

Other countries in Southeast Asia also had the same
constraints relating to the limited financial resources
available. Administrative problems occurred because of the
lack of general services to support antimalarial programs.
Shortage of trained manpower and the associated

difficulties of attracting and keeping trained personnel

23

were also constraints to the programs. At the same time,
inaccessibility of remote areas and political insecurity in
some highly malarious areas constrained the success of
control programs. Moreover, inadequate rural health
services, the lack of inter-sectoral cooperation, and
increasing costs of materials and equipment increased

malaria control difficulties (Harinasuta et al., 1982).

W

Generally, insecticide spraying, mass chemoprophylaxis,
and mass drug administration are very effective
interventions in malaria control. If practiced for a
sufficiently long period of time, the malaria reservoir may
even be eliminated. However, if the level of
administrative efficiency of these interventions drops, or
interventions are discontinued, malaria returns to high
levels of endemicity (WHO, 1986c).

Analysis of epidemiological data has shown that in
areas where DDT is sprayed, the API has remained more or
less at the same level, while in areas where spraying has
been discontinued, the API has increased. Where budgetary
and administrative obstacles resulted in discontinuing
control operations, this discontinuance gave rise to an
increase in malaria incidence (WHO, 1980). At the same
time, the worldwide spread of vectors resistant to DDT and

the resistance by the Anophelee population to other

24

residual insecticides such as dieldrin, HCH, and malathion
in several countries have made the chances of successful
control much more difficult (WHO, 1980). Moreover, vector
adaptation, in terms of changing behavior transmission
responses to outdoors where they were unable to be attacked
by indoor spraying, was considered to be one of the factors
contributing to malaria control problems (Pinder, 1973).

In Java, Indonesia, resistance to DDT of the Anopheles
aciotus vector has been reported for many years. Recent
findings revealed that resistance to insecticides has
increased, but DDT is continually used with varying degrees
of success. In Nepal, A. culcifacies has developed
resistance to DDT, and the control operation has shifted
from DDT to malathion spraying on a selective basis. In
India, A. stephensi, the major vector of malaria in urban
areas, has shown resistance to DDT and HCH. In addition,
A. pulcifacies were found in both rural and urban areas.
In Sri Lanka, DDT resistance in A. culcifacies led to the
use of malathion and fenitrothion spraying, which brought
about a dramatic reduction in the incidence of 2.
faleiparum malaria. In Burma and Thailand, DDT is
continually used regardless of the decrease in vector
susceptibility to DDT (WHO, 1980).

As a consequence of DDT resistance, the insecticide
used in malaria control programs in some countries has

changed from the long-lasting and relatively cheap DDT to

25

dieldrin/HCH and then to other organophosphate compounds
such as malathion. Since the new insecticides are largely
petroleum products, and there is inflation caused by the
oil crisis, their cost is not only three to five times
higher, but they also require more frequent applications.
Thus, expenditures on vector control have greatly
increased. This compounds the effects of additional
operational expenses from transport and labor. The cost
of national vector control programs in these countries has
reached or exceeds levels acceptable to the governments

(WHO, 1980).

Drus_3s§isfanss

In areas where multiple-resistance of vectors to
insecticides is a problem, increased reliance has been
placed on antimalarial drugs as a means of controlling
malaria (Pan American Health Organization [PAHO], 1984).
At the same time, the intensity of transmission, amount of
drug pressure and immune status of the population are
important factors in the development and spread of
pleempgipm resistance. For instance, as chloroquine is
used for both treatment and chemoprophylaxis, drug
resistance appears, and tends to increase more rapidly.
Likewise, the development of resistance to other drugs by
the malaria parasite, especially g. feleipeppm, further

reduces the chance of control in many regions where the

26

disease is endemic (PAHO, 1980; WHO, 1986a).

Quinine is the recommended initial treatment for
severe and complicated falciparum malaria. Treatment turns
into resistance when it runs too short a course or when it
is administered in inadequate doses. While 2. falciparum
resistance to quinine first appeared in 1910, in Brazil, it
did not occur in eastern Thailand until 1980. Resistance
of g. falciparum to chloroquine was independently and
almost simultaneously reported from Venezuela in 1960,
Colombia in 1961, and Thailand in 1962. The following
year, chloroquine resistance was reported in additional
countries in eastern Asia. Chloroquine resistance in Asia
continued spreading outward from the Indochinese Peninsula
to southern India, Pakistan, and Nepal (Spencer and Thomas,
1985; Verdrager, 1986). South America and East Africa
were also affected by chloroquine resistance, and this
problem assumed worldwide significance (PAHO, 1984).

As a result of drug resistance, there is an increasing
problem of clinical prevention and treatment of
2. falciparum over a large part of its geographical
distribution.

Spcioeconomic and Culpural Factors
Population movement is an important factor in terms of
disease occurrence and spread of resistance (Verdrager,

1986: WHO, 1986b). Population movement to and from

27

malarial areas is of great epidemiological importance.

The rapid growth of periurban places and slums around the
city as the result of rural to urban movement is likely to
lead to increased malaria transmission due to primitive
sanitary conditions, the creation of vector breeding
places, and lack of medical care. Population movements-
from rural to urban areas in the case of Punjab, Pakistan
and in India were responsible for increasing malaria cases
in urban areas. In many circumstances, the outbreak of
malaria is introduced by people moving from politically
disturbed areas where there is still active transmission
of malaria into a neighboring country where transmission
has been considerably reduced. Population movement is an
obstacle in malaria control because of the difficulties
encountered in maintaining contact with people in order to
spray dwellings and to distribute antimalarial drugs.

In addition to the above, malaria can be imported by
persons normalling travelling to and from malaria infected
countries. In Singapore during the decade 1979-1988, one
or more deaths in almost 200 cases reported, were acquired
in malarial areas outside the country (Goh, 1985). In
Europe in 1979, from 4,000 cases reported, most of the
infections were contracted in the Indian subcontinent or in
Africa (Manson-Bahr and Apted, 1982).

Besides the problems of population movements and

human behavior, the aggregation of laborers connected with

28

the application of green revolution practices and other
economic development projects are also considered as
factors contributing to the resurgence of malaria. The
creation of water reservoirs which turn into breeding
places serve as examples. Development projects such as
construction dams and roads provide new breeding sites for
mosquitoes (WHO, 1974) and the extensive use of pesticides
needed to maximize the yields of cash crops causes
insecticide resistance in Anopheles (Chapin and
Wasserstrom, 1983; WHO, 1986c: Wyler, 1983).

Attitudes, religious beliefs, and traditions can be
barriers in malaria control. For example, many rural
population do not understand why malaria should be selected
for elimination rather than poverty, hunger, or even other
diseases (Gramiccia, 1981; MacCormack, 1983). In many
cases, opposition to DDT spraying occurs because people
feel that residual insecticide deposits damage iron roofs,
internal compounds, and household furniture, and are also
toxic to their domestic animals (Hongvivatana, Leerapan,
and Smithsampan, 1982). The smell is also unpleasant.
Religious beliefs constitute a serious barrier, for
example, people in the tribal areas of India often forbid
spraying on religious wall paintings. Replastering of walls
with mud wipes out the effect of insecticides.

In simpler term, the introduction of DDT and related

insecticides to control malaria have had a dramatic impact

29

on the Apophelee mosquito population, and consequently, on
the world wide incidence of malaria. Malaria has
decreased, resurged, and again decreased, though not to the
same levels of the initial decrease. Not only technical,
but also political, socioeconomic, and cultural factors

continue to affect malaria control.

Chapter 3
Methods of Analysis and

Sources of Data on Malaria in Thailand

Significant data to encompass all the research
questions introduced in chapter one p. 3, depend upon
malaria mortality rates and malaria morbidity rates, which
are employed as follows:

1. Trends of malaria mortality are determined from a
time series of malaria mortality rates from 1943-1986. The
malaria mortality rate is defined as the relative frequency
of malaria deaths to midyear population and standardized to
100,000 population.

No. of malaria deaths

Malaria Mortality Rate a * 100,000
(MMR) Midyear population

 

Then the rates of change, the summary measurement of change
in the level and trends of malaria mortality rates are
employed to analyze malaria mortality trends.
(MMR year2 - MMR yearl)
Rate of change of MMR = * 100
MMR yearl
2. General demographic characteristics of Thai people

who have died of malaria are examined by malaria
mortality rates by sex and age group. Malaria mortality

rates by sex are also presented in standardized form, and

30

31

malaria mortality by age group is presented in percentage
form.

No. of male deaths from malaria

MMR male * 100,000

 

Male midyear population

Percentage of malaria mortality by age groups
No. of deaths in a specific age group
= Total of malaria deaths * 100
3. Time and climatic conditions of malaria occurrence
are determined from the two series of the data. First, a
monthly series of the number of reported malaria cases by
province from 1985-1988 is standardized and averaged to be
monthly malaria morbidity rates of 1985-1988. Malaria
morbidity is indicated by the annual parasite incidence
(API) rate. The parasite found in the individual is
examined by a blood smear. Positive blood film tests
indicate malaria sickness. Generally, the API rate is the
proportion of malaria cases to the unit of population in
which malaria occurs, standardized to 1,000 population.
No. of malaria positive cases
API rate = * 1,000
Midyear population
Second, a time series of climatological data, i.e.,
mean temperature (0 C), relative humidity (%), and rainfall

(mm) of the years 1956-1985, recorded in months from every

station in the country, including a similar set of data for

32

the subsequent years from 1986-88, are averaged to be
monthly climatological data of 1956-1988. These data
showing long term trends are assumed to be the general
stable climatic conditions of Thailand. The average
monthly climatological data are converted into temperature
in fahrenheit degrees, and rainfall in inches. This graphic
method is used to examine the linkage between time and
climatic conditions of malaria occurrences. However, since
averaged monthly API rate is a very small unit, ranging
from 0.32 to 0.63 per 1,000 population, the API rate is
multiplied by 10 in order to make it easier to analyse and
visualize comparable graphic to the climatological set of
data.

4. Trends and the present distribution of malaria in
Thailand are examined from yearly malaria morbidity rates.
Similar standardized data are employed. Yearly API
rates from 1972-1988 are graphed to analyze morbidity
trends.

In addition, API rates of the years 1977-1988 from
individual provinces (73 provinces) are mapped by computer.
The variations of malaria incidence rates are shown by
choropleth maps. As a first step, provincial boundaries
are digitized to produce Thailand's base map file. Next,
annual parasite incidence rates by provinces are
transformed to the data file. As a second step, both files

are merged into the ATLAS*GRAPHICS program. A series of

33

choropleth maps from the years 1977-1988 are produced on
the basis of frequency distribution, and cutoff points are
categorized to allocate five areas of malaria incidence
classes. API rates ranging from 0.0-10.0 per 1,000
population are grouped as a very low malarial area. API
rates ranging from 10.1-30.0 per 1,000 population indicate
a low malarial area. API rates ranging from 30.1-50.0 per
1,000 population are categorized as a medium malarial area.
API rates ranging from 50.1 to 70.0 per 1,000 population
indicate the medium high malarial area. Finally, API rates
ranging from 70.1 to as high as 202.3 per 1,000 population

are grouped as a high malarial area.

Sources of Date

Generally, Thai government institutions collect and
compile their data on a fiscal yearly basis from October to
September. Therefore, yearly data in this study, as
mentioned in method of analysis number one, two, and four,
are presented in the fiscal year, except for number three
which is presented monthly as in the calendar year. The
sources of data in this study are derived from the
following Thai institutions.

1. Data on time series of the malaria mortality rate
and its classified components of sex and the age group
obtained from the Division of Health Statistics, Office of

Permanent Secretary, Ministry of Public Health, Thailand.

34

2. Data on yearly and monthly malaria morbidity
collected and compiled from the Division of Malaria,
Department of Communicable Diseases, Ministry of Public
Health, Thailand.

3. Climatological data refined from the records of the

Meteorological Department, Ministry of Communication,

Thailand.

Limitation of the §tudy

At the time of this study, only limited recent
socioeconomic-demographic and physical environment
information is accessible at the provincial level rather
than the regional level. Hence, in this study many social
factors and micro-environmental factors that may contribute
to the malaria control program are descriptive, not

examined in depth.

Chapter 4
Geographical Profile of Thailand and

Malaria Transmission and Control

s nv' onme

Thailand is located in Southeast Asia and lies between
970 and 1060 east longitude, and 50 and 210 north latitude.
Bordered by Burma to the west, Laos to the north and
northeast, Kampuchea to the east, and Malaysia to the
south, Thailand's area is about 198,000 sq. mi. (513,115
sq. km.). Cultivated land comprises 44 percent of the
total area and an additional 25 percent of the land area is
forested (National Identity Office, 1984).

On geographic and administrative grounds, the country
is divided into four diverse geographical regions: the
Northern and Western Mountain Region, the Northeastern
Khorat Plateau Region, the Central Lowland Region, and the
Southern Peninsular Region. The Northern and Western
Mountain Region is thickly covered by forest, yielding
valuable timber. Running parallel to the north-south
mountain ranges are valleys of four rivers which flow
southward through flat, swampy ground before reaching the
central plain of the country. The Northeastern Khorat
Plateau Region is not geographically favored. It has many
ecological problems such as poor soils, a dry plateau and a

large basin with rolling hills. The land surface is swampy

35

36

with many lakes. Its two large rivers are close to the
Mekhong River, the natural boundary between Thailand and
Laos.

The Central Lowland Region formed by the Chao Phraya
River is the center of the country. In the southeastern
part of this region, there is more forest and rainfall.)
This portion situated between the Chanthaburi Mountains and
the Gulf of Thailand is drained by numerous small streams,
which flow in a southerly direction. The Chanthaburi plain
is bordered by the Banthat Hills on the east along the
Kampuchea frontier. The Southern Peninsular Region is
mountainous and contains little flat land. To its east
lies the Gulf of Thailand and the South China Sea. The
narrow southern boundary with Malaysia is the hilly
Kalakhiri Range. Unlike the Northeast, this region has
numerous small streams, and no large river (Sternstein,
1976; Gerberg and Graham, 1978: Kaplan, 1981).

According to Koppen’s classification on the basis of
rainfall, temperature conditions, and the pattern of
vegetation (Pendleton, 1962), most of the country i.e. the
north, northeast, and central plain shares a tropical
savanna climate (Aw), dry from November through April, with
rain from the southwest monsoon between May and October.
The section of the Southeast Coast (IV) and the Western
Mountains (IIB), as well as, provinces in the Peninsular

South (VB), except for a few lowland coastal sections of

37

the east coast, are classified as Tropical Monsoon Climate
(AM), (see Figure Bl in Appendix B). The east coast and the
southern peninsula have climate with a very short dry
season and a very heavy annual rainfall, and the
peninsula’s east coast below Nakhon Si Thammarat (46) has a
tropical rain forest climate, humid throughout the year.
(see Figure B1 and Figure B2 in Appendix B). Average
precipitation varies among different parts of the country
with 40-60 inches in the Northern Mountains and 80-120
inches in the Western mountains and most of the Southern
Peninsula. The average temperature for the country is
about 81.7 0F (27.6 0C). The average humidity is 74.4
percent.

Shifting cultivation is common in the north mountain
range from which valuable logs of teak and other timbers
are sent south via the Salaween in Burma and Chao Phraya
River. The western hills have always been an isolated
area, known mainly for their timber and for the Karen
people, a large ethnic group in Burma. The Northeastern
Khorat Plateau is today agriculturally diversified
producing maize, cotton, tobacco, and kerna.. Bangkok in
the Central Lowland is the capital city, the center of Thai
politics, culture, and economics. The southeast coast can
be considered a political and cultural extension of the
central plain, even though its geology, soil, and climate

differ. The economy of the far south is based on the

38

mining of tin and on extensive trade and cultural relations

with the Malay (Wilson, 1983).

The population of Thailand was estimated to be 53.9
million in 1987, with an annual growth rate of 1.9 percent
and 38 percent of the population under age 15. The average
population density is 70.7 persons per sq.km. Thailand’s
population is still predominantly rural, with approximately
85 percent of the population living in rural areas.
Increased productivity and expansion in the agricultural
sector have given rise to economic growth and increased
employment opportunities. However, the share of GDP
attributed to industrial and service sectors growth has
been increasing. The per capita GNP is in $810 US per
year. The overall literacy index is 85.5 percent, with an
89 percent literacy rate for male and 75 percent for
females (National Identity Office, 1984).

Thailand’s population is considered to be homogeneous;
in 1980, 95.5 percent of the population is Thai-speaking
Buddhist, though there are marked differences in dialect
and culture among the country’s major regions. The main
minority groups are in the northern and southern extreme of
the country. In the northern hills, bordering Burma and
Laos, some 400,000-500,000 are assorted hill tribesmen.

They are differentiated from each other and from the Thai

39

by custom and language. In the far south of the country,
one million Thai Moslems make up the largest religious
minority of the country. Like much of Southeast Asia,
Thailand absorbed a substantial influx of Chinese in the
period of European colonial expansion. Over 3 million
Chinese in Thailand are widely assimilated and
intermarried: they are a large and important social and
political minority. Additional minority groups include
the Indian, Pakistan, Khmer, and Vietnamese descendants.
Thailand has a crude birth rate of 25 per thousand, a
crude death rate of 6 per thousand, and an infant mortality
rate of 51 per thousand. The life expectancy at birth is
63 years (Division of Health Statistics, 1986). Health
care in Thailand is provided throughout the country by a
network of hospitals, regional health centers, clinics,
local midwiferies, and health stations. The health-service
system in Thailand is a complex mixture of public and
private providers. Private health service are very
important in urban areas. On the other hand the public
health sector provides health care for the large rural
population. Access to medical care and to trained
physicians is primarily localized in Bangkok, and in
provincial and some districts towns. Some people are in a
stage of transition from traditional to modern medical
practices. Traditional Thai medicine mixes Chinese and

Indian therapies which have been developed through trial

40

and error over the centuries. The traditional practices
are affected by Buddhist and animistic beliefs. However,
all matters concerning the health of the nation are
officially controlled through the exclusive responsibility
of the Ministry of Public Health (Gerberg and Graham,1978).
Currently, Thailand divides its administrative areas
into 73 provinces (Changwat, see Figure B3 in Appendix
B). Bangkok metropolitan is the capital city and a
primate city. Each province is further subdivided into
districts (amphoe), subdistricts or townships (tambon)
and villages (muban). According to 1980 census, the
urban percentage is 24 percent. This figure includes

municipal areas and large sanitary districts.

Malaria Vectors and Malaria Parasites

In Thailand most malaria vector breeding occurs in
foothill areas where appropriate temperature, humidity and
rainfall conditions exist, especially in border areas where
forests are abundant. The rainy season, which runs from
mid May to July, is the period of the year when there is
the largest increase in numbers of malaria mosquitoes. The
three principal species of Anopheline mosquitoes
responsible for malaria transmission are A. glrpe also
known as A. balabacensi , A. minimus, and A. maculatus.

These three species require different ecological conditions

41

which bring about different geographical distributions of

the disease.

A. dirus is considered to be the most important vector

 

in Thailand. It is the species in which the resistant
falciparum strains have been detected (Scanlon and
Sandhinand, 1965). Its area of prevalence is associated
with the distribution of forest and forest fringe areas.
Because of infringement of agriculture and the cutting of
lowland forest areas, the species is now confined primarily
to the foothill and mountainous forests. Malaria
transmitted by this species is now extremely difficult to
control by residual spraying (Prasittisuk, 1985). A. dirpe
is unevenly distributed throughout most of Thailand, except
for the Khorat Plateau and the non-jungle areas of the
central Lowlands and peninsula. A. dippe has been reported
from areas of less than 100 m. in elevation to as high as
1200 m. The adult females are highly anthropophilic and
exophilic. They rest in the forest vegetation during the
day and congregate in the vicinity of human dwellings
before dark. The larvae are usually found in various types
of temporary pools, preferably shaded, shallow in sandy
areas. A. glppe may also be found in muddy animal wallows,
hoofprints, footprints, wheel ruts, and other temporary
water collections.

A. minimge is another predominant vector in

Thailand. A. minimus was previously found in the plain

42

but disappeared after use of DDT. Unlike A. gippe, its
prevalence is in the forested and cleared forested
foothill area with slow running streams. It occurs
throughout most of the country except the central Khorat
Plateau, Bangkok, the North, and near the Northwest Gulf
of Thailand. Its density is also lower in the southern.
peninsula.

The behavior of adult A. minimus females is
anthropophilic. The adults may rest in houses during the
daytime, usually in places less than 8 ft. above the
floor. Their feeding usually begins after dusk and
continues throughout the night. Adult females are early
dusk biters during the dry season and are late nighttime
biters in the rainy season. The adult density decreases
in December, with the lowest levels in March. The
habitat of the larvae is usually in shady grassy edges of
sunlit and partially shaded streams, where there is
clear, flowing water. Larvae are also quite prevalent in
the grassy overgrown margins of irrigation ditches and
drains.

A. maculatus is another principal malaria vector,
restricted predominantly to the southern part of the
country. It is widely distributed in the hilly area
where breeding takes place in clean streams and seepages

Open to the sun.

43

Besides these three species, A. sundaicus and A;
aconitus are two additional vectors found in some
particular areas (Cullen, Chitprarop, Doberstyn, and
Sombatwattanangkul, 1983; Prasittisuk, 1985).

The three species of Plasmodium parasite in Thailand
are: 2. falci arum, g. yiyex, and 2. malariae. Serious
infection is predominantly caused by E. felciparum. In
1985, g. falciparum had the highest prevalence and

accounted for 65.3 percent of malaria cases. 2. vivax

 

accounted for 34.4% and only 0.02 percent was due to P.

malariae in the same year (Prasittsuk, 1988).

Established Malaria Copprpl in Thailand

Anti-malaria operations started in Chaing Mai, a
province in northern Thailand, in 1930. The following year
two more malaria control units were formed in Prabuddhabat
district and Khon Kaen province. A malaria section was
established in the Ministry of Public Health in 1934, with
the chief functions of carrying out limited malaria surveys
and of administering quinine. In 1949, the WHO and the
UNICEF funded and supplied technical personnel for a pilot
project in Chaing Mai province. The project, which
advocated the spraying of DDT to control malarial
mosquitoes, was a remarkable success in terms of decreasing
the incidence of malaria. In 1951, the government of

Thailand, with the USAID assistance, developed a country

44

wide malaria control program. By 1964, the program
expanded from control to eradication. Though complete
coverage of malarious areas by DDT spraying had not been
achieved, vast areas were cleared of endemic malaria
(Pinichpongse, 1982).

According to Pinichpongse (1984) the Anti-malaria
Program attempted to provide a framework for control
operations by dividing the country into two areas which
differed in their incidence of malaria. The two areas were
defined as follows:

1. Control Area, consisting of forested hills and
mountains, border areas, and insecure areas with a
population of approximately 10.5 million

2. Eradication Area, consisting of the major part of the

country with a population of approximately 38.5
million.

The strategy presently implemented is that of long-term
malaria control in the forested and hilly areas of the
country where malaria is endemic (Control Area), and
prevention of the reestablishment of malaria
transmission in the remaining areas where a malaria
eradication strategy is being applied (Eradication Area).
For operational purposes, malaria control is presently
divided into five regions, 33 units, and 302 sectors
covering 73 provinces. Control measures vary according to
the local epidemiological situation. The main control
measure is residual insecticide house spraying with
DDT/Fenitrothion once or twice a year. The other two

important control measures are: radical treatment with

anti-malaria drugs which is provided by the malaria

45

clinics, and health education. Additional supplemental
control measures are use of larvicide, mass chemotherapy,
space spraying, case detection and treatment, and the use
of larvivorous fish (Prasittisuk, 1985).

Besides the standard control measures mentioned
above, the government established a primary health care‘
project in 1961 designed to provide appropriate health
care delivery to all individuals. The program recruited
volunteers from the local vicinity to work as Village
Voluntary Malaria Collaborators (VCC) in endemic malarial
areas. The program provided an initial one or two day
training course for these volunteers, and also supervision
for them. Refresher courses were given as needed. These
volunteers assisted in the spraying operations and in
taking blood smears from and giving presumptive treatment
to any villager who is suspected of having malaria. The
program is still in existence today.

The goals of the Anti-malaria Program, as set out in
the current National Health Plan (1982-1986) are as
follows:

To reduce mortality caused by malaria to less than
8/100,000:

To reduce the morbidity caused by malaria in control
areas to less than 12 per 1,000;

To prevent the reintroduction and transmission of malaria
in eradication areas by having not more than 1
indigenous case per 10,000 population and;

To implement a primary health care approach to malaria

control and to involve the local communities in
personal protection measures.

Chapter 5

Results and Discussion

This chapter analyzes and discusses the malaria
situation in Thailand. Section 1 deals with general trends
of malaria mortality rates from 1943 to 1986, as well as
the demographic characteristics of afflicted groups.
Section 2 focuses on malaria morbidity rates and
investigates trends of malaria incidence from 1977 to 1988,
and the climatic conditions associated with malaria during
1985-1988, including geographic patterns and influences

relevant to the incidence.

Ge e a s ' a ' e ' ' n

The long-term trends in malaria mortality rates in
Thailand follow the global pattern of malaria control that
has declined and resurged. According to the health
statistics of Thailand, malaria has been recorded as being
the leading cause of death. Approximately 40,000-50,000
people died annually before the year 1949, and the actual
number of malaria deaths may be twice these reported
numbers (Pinichpongse, 1984). Table 5.1 illustrates the
magnitude of malaria mortality rates per 100,000 population
and its rate of change from 1943-1986.

In 1943, malaria mortality rates were 351.1 per

100,000 population and were approximately 300 per 100,000

46

47

population in 1947 (Pinichpongse, 1982). In 1949,
household DDT spraying was initiated as a pilot project.
the dramatic results of this project resulted in the
formation of a country-wide Malaria Control Program in
1951-1957, with the assistance from the World Health
Organization (WHO), the United Nations Children's Fund
(UNICEF), and the United States Agency for International
Development (USAID). In this period, DDT was applied as a
major control measure, and the program covered up to 12
million people. The death rates dropped from 205.5 per
100,000 population in 1949, to 37.8 per 100,000 population
in 1958. The rates of change in malaria deaths constantly
decreased from 7.6 percent at the beginning of the DDT
control program, to 28.7 percent in the middle of the
program in 1953. This change is the largest decline of
malaria in the history of Thailand. It appeared that the
malaria control program reduced malaria from the first
leading cause of death to the fifth by 1958. Overall this
decrease represented a change of 82 percent from 1949 to
1958.

Beginning in 1963, a joint WHO/USAID program was
carried out in collaboration with the Thai Malaria Program.
This collaborative program was successful. The malaria
program changed its aim from control to eradication, and
its first plan was operational in 1965. In 1963 to 1970,

the malaria mortality rates had decreased annually from

48

22.8 to 10.1 per 100,000 population. Between 1949 and
1970, $61,010,000 US was spent on the program to help
achieve this reduction (Gerberg and Graham, 1978). The
decline in death rates during this period is generally
regarded as a consequence not only of applying DDT which
interrupted malaria transmission, but also of extending'
malaria surveillance for early detection of cases.

The progressive decrease in mortality continued
until 1970 when budget constraints had a negative impact on
the malaria eradication program. Figure 5.1 to Figure 5.3
illustrates malaria mortality rates and rate of change
between 1943 to 1986. The downward trend of malaria deaths
from 1950's to 1960's ended in 1970. From 1971, 1973, and
1974, the country experienced an increase in the malaria
death rates from 12.5 to 14.4 per 100,000 population. The
change increased to 23.8 percent in 1971, to 25.7 percent
in 1973, and to 11.3 percent in 1974. These increases
coincided with the end of the donor assistance in 1968 to
1970, when USAID withdrew aid given in the form of
insecticide for eradication, transportation of supplies,
fellowships for training, and other materials to combat the
malaria. In addition in 1972, the United States Operations
Mission (USOM) research unit withdrew the assistantship
that provided both basic and applied epidemiological and
entomological knowledge of malaria (Gerberg and Graham,

1978). Lack of this information, possibly, may have

49

resulted in an inadequate warning system, a delay in
recognizing the acceleration of malaria (Cullen et al.,
1984), and failure to implement the necessary preventive
and curative measures in time. WHO documented that a
reduction in surveillance can lead to a reappearance of the
disease (WHO, 1986c).

Financial problems may have contributed to a decrease
in insecticide usage and area coverage under the plan,
making malaria control difficult. In addition, increases
in malaria deaths probably can be associated with the
political unrest in Kampuchea, Vietnam, and Laos which
ended in 1975. Infected persons, military personnel,
peddlers, and others involved in this region, may have
contributed to the spread of malaria deaths during those
years. It also should be noted that the parasite 2.
falciparum developed a resistance to the drug, chloroquine,
as first reported in 1962 (Pinichpongse, 1982).

Since 1972 then, the Thai eradication program
continued its activities under the regular Royal Thai
Government budget. As a consequence of the WHO’s
reevaluation and reexamination of the worldwide strategy
for malaria eradication, and to meet the Thai budget, the
National Malaria Eradication Project was revised to the
Malaria Control Operation Program with the objective of
maintaining the designated control areas and preventing the

potential new problem areas. From 1975 to 1986, malaria

50

mortality rates have dropped continuously from 14.4 in 1975
to 2.9 per 100,000 population. The provision of peripheral
health care delivery and the establishment of malaria
clinics have contributed to a tangible decrease in malaria
deaths since 1975. (Prasittisuk, 1985).

Despite a steady decline in malaria death from 1975 to
1980, a second peak was observed in 1981. Malaria
mortality rates in 1980 were 8.1 increasing to 8.6 per
100,000 population in 1981. Nonetheless, this increase was
only 6.2 percent, approximately one to two fold less than
the first peak, during 1971-1974, with increasing changes
varying from 25.3 to 11.3 percent. The new rise of malaria
death was attributed mainly to population movements to live
and work in mosquito-infested transmission areas, as well
as widely observed the 2. feleiperpm parasite resistance to
antimalarial drugs such as chloroquine, the drug of choice,
and other radical drug treatments, including the
Sulfadoxine-pyrimethamine combination. (Prasittisuk, 1988).

During the 1950s and 1960s economic development of the
country appears to increased in tandem with this steady
decline in malaria deaths during the successful DDT
campaigns. Use of modern technology after World War II and
the investment in infrastructure in many parts of the
country improving the overall health and sanitation of Thai
people, may have had some impacts on malaria deaths. Thai

economic growth rate averaged 4.7 percent annually between

51

1951 and 1958 and 8.6 percent between 1959 and 1969, and
dropped in the early 1970s (Constance, 1983).
Interestingly, the first peak of malaria deaths was
observed in 1971. The growth rate of real GDP was high as
8.9 percent annually in 1975-1979 despite the crisis caused
by rising oil prices at the beginning of that period. The
economic growth rate dropped after 1979. During 1980-1982,
the growth rates of GDP were 5.4, 4.8, and 4.1 percent, but
the rate bounded back to around 7 percent in 1987-1988 (The
Economist Intelligence Unit [EIU], 1988). Furthermore, a
noticeable shift of the labor force, from the agricultural
sector to other sectors, especially toward the
manufacturing sector, during the 1960s-1980s (see Table 5.2
from Knodel, Chamratriththirong, and Debavalya, 1987), may
have contributed somewhat to fewer people being exposed to
malaria, predominantly endemic in rural areas: the shift
coupled with effective medical care has contributed to
fewer malaria deaths, at the present time. The malaria
mortality rates dropped each year from 7.8 in 1982 to 2.9
per 100,000 population in 1986. The change decreased as
nearly the same as at the beginning of the start of the DDT
program. For example, the rate of change was 25.6 percent

in 1986 compared to 28.7 in 1953 and 25.4 percent in 1954.

52

Table 5.1 Malaria Mortality Rates and Rate of Change:
1943-1986 (Rates per 100,000 Population).

 

 

Year Malaria Mortality % Change in GDP ‘°+_
Rates Malaria Deaths Growth Rates
1943 351.1
47* 2300.0
49 205.5
1950 183.1 -10.9
51 169.1 - 7.6 -----------
52 139.2 -17.7
53 99.3 -28.7
54 73.9 -25.4
55 63.2 -14.5 ave.= 4.7%
56 53.3 -15.7
57 43.0 -19.3
58 37.8 -12.1 -----------
59 33.2 -12.2 ...........
1960 30.2 - 9.0
61 24.5 -18.9
62 24.3 - 0.8
63 22.8 - 6.2
64 18.2 -20.2
65 15.2 -16.5 ave. 8.6%
66 14.7 - 3.3
67** 12.9 -12.2
68 10.4 -l9.4
69 10.4 0.0 ...........
1970 10.1 - 2.9
71*** 12-5 +23.8
72 11.3 - 9.6 ave. 6.5%
73 14.2 +25.7
74 15.8 +11.3
75 14.4 - 8.9 -----------
76 11.5 -20.1
77 10.9 - 5.2 8.9%
78 10.2 - 6.4 ----------
79 8.2 -l9.6 5.0
1980 8.1 — 1.2 5.4%
81 8.6 + 6.2 4.8 %
82 7.8 - 9.3 4.1%
83 5.9 -24.4
84 4.4 925.4
85 3.9 -11.4
86 2.9 -25.6 7.1 %

 

Source: Annual Report, Division of Health statistics,
Ministry of Public Health, Thailand.
Note. a From C.M. Wilson (1983) and EIU (1988).
* 1949 Started DDT operations.
** 1968 Reduction of financial supported for DDT.
*** 1972 Complete withdrawal of financial support.

53

Table 5.2 Percentage Distribution of the Economic Active

Population Aged 11 and Over, by Industry:
1960-1980, and by Residence, 1980.

 

1980

 

1960 1970 1980 Rural Urban

 

Agriculture (including
forestry hunting, and

fishing) 82.4 79.3 72.2 82.8 7.1
Manufacturing 3.4 4.1 5.6 3.6 18.0
Construction (including

repair demolition) 0.5 1.1 1.5 1.0 4.7
Commerce 5.7 5.3 7.3 4.1 27.1

Transport, Storage, and

Communication) 1.2 1.6 1.8 1.0 6.8
Services 4.8 7.1 8.1 4.6 29.3
Others, Unknown 2.0 1.5 3.4 2.8 7.0

 

Note.

 

From Thailand'e Reproductive Revolution: Rapid
Fertility Decline in a Thipd-World Setting (p. 36)
by Knodel, J.E., Chamratriththirong, A., and
Debavalya, D., (1987), Madison: University of
Wisconsin Press.

1960 and 1970 censuses as reported by Pejaranonda
and Arnold (1983) and 1980 census report.

The economically active population refers to all
persons who were employed at the census date or at
any time during the preceding twelve months.
Forestry, hunting, and fishing constitute only a
very small percentage of this group; in 1980, for
example, they represented less than 0.5 percent of
the economically active population.

Combined with banking and other related financial
institutions in 1980 and presumedly for prior years.

In summary then, with the notable exception of two

reappearances in 1971 and 1981, ten years apart, there has

been a steady decline in malaria deaths in Thailand over

the past 40 years. This reflects very successful control

(see Figure 5.2 and 5.3).

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55

Malaria Mortality Rates by Sex and Age Group

Table 5.3 and Figure 5.4 show malaria mortality rates
by sex from 1977-1986. Malaria mortality rates for
individual sexes also show decline for both sexes. It is
notable that the male, in contrast to the female, has the
greater number of malaria deaths. This pattern has
remained rather consistent from 1977 through 1986. The
ratio of male deaths to female deaths ranged from
approximately 1.5:1.0 in 1977 to l.8:1.0 in 1986. During
1977-1980, the ratio of male deaths to female deaths
averaged 1.65:1.0. The reappearance of national malaria
mortality in 1981, is reflected in male deaths far more
than in female deaths. The male death rate was 10.7 per
100,000 population, whereas the female death rate was 6.4
per 100,000 population in the same year. The ratio of male
deaths to female deaths in 1981 was 1.8:1.0. A comparison
of malaria mortality rates by sex during the period of
1977-1981, shows that male mortality rates fluctuated more
and were greater proportion than female mortality rates.
From 1982 to 1986, the figures showed decreasing malaria
mortality rates for both males and females. The male death
rate was 9.6 in 1982 and decreased to 3.8 per 100,000
population in 1986; at the same time, the female death rate
was 6.0 and dropped to 2.1 per 100,000 population. The
figures for the ratio of malaria mortality rates of male to

female are rather constant, male deaths having a greater

56

number than female; however, the recent ratio of male
deaths to female deaths shows a growth tendency, with an
average ratio of 1.62:1.0 from 1977 through 1981, and the
average ratio of 1.68:1.0 for the five year period from

1982 through 1986.

Table 5.3 Malaria Mortality Rates combined male and by Sex,
1977-1986 (Rates per 100,000 Population).

 

(1) (2) (3) (4) (5)
Year No. of All Death Male Death Female Death Ratio

 

Deaths Rates Rates Rates Male:Female
1977 4771 10.9 13.0 8.6 1.5
78 4595 10.2 12.3 6.1 2.0
79 3787 8.2 9.9 6.5 1.5
80 3755 8.1 10.0 6.1 1.6
81 4071 8.6 10.7 6.4 1.8 *
average = 1.62
1982 3779 7.8 9.6 6.0 1.6
83 2898 5.9 7.3 4.4 1.7
84 2221 4.4 5.5 3.3 1.7
85 1829 3.5 4.4 2.7 1.6
86 1540 2 9 3.8 2.1 1.8 *
average = 1.68

 

Source: (1)-(4) Annual Report, Division of Health Statistics,
Ministry of Public Health, Thailand.
(5) Calculated from (3) and (4).

Note. * Unweighted.

OO-I\..—-I

flo—fll—CUO'U 00°-

 

57

 

 

- Male

.15 Female

Figure 5.4 Malaria Mortality Rates
by Sex. 1977-1986.

58

Unlike the malaria mortality rates by sex, the figures
for malaria mortality by age group presented in Table 5.4
are measured as the percentage of number of total malaria
deaths in an interval of age group to the total number of
malaria deaths. Figure 5.5 shows the percentage of malaria
mortality by age group for 1982-1986. Most deaths from
malaria in the five year period of 1982-1986, occurred in
young adults, working-aged of 15-24 years, with a rate of
over 20 percent each year. The other five groups had
malaria deaths higher than 10 percent but lower than 20
percent. These populations were in age groups of 0-4,
5-14, 25-34, 35-44, and 45-54 years. The last two groups
aged 55-64 years and 65 years and over had malaria deaths
lower than 10 percent. While infants and children in Burma
did not show any significant difference in malaria
incidence (Kondrashin, 1986), Thai children of 5-14 years
of age, were within the second highest group of malaria
death. Deaths in this age group varied from 13.1 percent
in 1984 to 19.8 percent in 1983. The third highest number
of malaria deaths occurred among the adult working group
between the ages of 25-34 years. Malaria mortality in this
group was 14.2 percent in 1982 and 15 percent in 1986. The
infant population between the ages of 0-4 years had the
fourth highest rank of deaths, ranging from 13.7 percent in
1982 to 9.5 percent in 1986. The groups of population

within the ages of 35-44 and 45-54 years experienced 10

59

percent of deaths due to malaria. Death in age groups of
55-64 and 65 years and over ranged from 5.2 to 7.6 percent.
By comparison, the percentage of malaria mortality
between the second highest group (age 5-14 years) and the
third highest group (age 25-34 years) indicate that, during
1984-1986, the adult working-aged group (25-34 years) had
an increase in the number of deaths, while the children’s
age group (5-14 years) decreased (see Figure 5.6). The
percentages of malaria deaths in the working-age group of
25-34 years were 15.0, 16.0, and 15.2 compared to 13.1,
14.3, and 14.4 in the 5-14 years group. Again, malaria
deaths appeared to increase with age, as seen in the middle
age groups (35-44 and 45-54 years) in comparison to the
infant group (0-4 years), since 1983 (see Figure 5.7). In
1983, malaria deaths in the age group 35-44 years was 13.5
percent, and 11.1 percent in the age group 45-54 years,
whereas the percentage of deaths in the infant group (0-4
years) was 10.7 in the same year. In 1986, the percentage
of deaths was 12.2 in the age group 35-44 years and 12.5 in
the 45-54 year age group compared to 9.5 percent in the
infant group (0-4 years). It should be pointed out that
since 1984 malaria deaths in Thailand have been relatively
high in adults, particularly, in the Thai population
working age of 15-24 years, as well as an increasing rate

in the 25-34 year group.

60

Table 5.4 Percentage of Malaria Mortality Male and

Female Combined by Age Group, 1982-1986.

 

Rank of Death

 

 

Age group 1982 1983 1984 1985 1986

1982 1986
0-4 13.7 10.7 11.5 10.1 9.5 4 6
5-14 17.0 19.8 13.1 14.3 14.4 2 3
15-24 22.8 21.6 24.3 23.4 21.1 1 1
25-34 14.2 14.3 15.0 16.0 15.2 3 2
35-44 10.7 13.5 12.0 11.6 12.2 6 5
45-54 10.8 11.1 11.8 10.6 12.5 5 4
55-64 5.2 7.1 6.9 6.8 7.5 8 8
65+ 5.6 5.9 6.0 7.2 7.6 7 7

 

Source: Annual Report, Division of Health Statistics,
Ministry of Public Health, Thailand, 1982-1986.
Detailed analyses of recent trends of malaria
mortality by sex and age suggests that a large portion of
males working-age group of 15-24 years are the worst
afflicted group, as are those aged 25-34 years. Similarly,
studies of the patients in Kanchanaburi (56), a province of
having moderately high rates of malaria incidence in
Thailand (see Figure 5.13), found that most of the patients
were male working group aged 16-30 years (Kanjanapan, 1981;
Hongvivatana, Leerapan, and Smithsampan, 1982). Possibly,
because of the greater outdoor exposure of the male
working-age group, they have more contact with mosquito
vectors, and thus, are more vulnerable to malaria
infection. In general males have a tendency to delay
seeking medical care, since they do not want to lose their
This behavior enhances

income, if they earn a daily wage.

the possibility of severe illness and death.

61

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62

Malaria Moppidipy Rates: Tpengs, Time. end Distribution

Malarie Morbidity Trends

Compared to a steady decline for over 40 years in
malaria mortality rates (except for rising deaths in 1971,
1973, 1974, and 1981), malaria morbidity rates in Thailand
during 1972-1988 showed fluctuation. The implementation of
DDT spraying programs in 1949 and the subsequent decline in
malaria deaths were consistent with decreasing malaria
incidence. The DDT spraying program played an important
role in reducing malaria incidence in Thailand during the
period of 1949-1960's. The annual parasite incidence rate,
the indicator of malaria illness, shows that in 1947 an API
rate was 286 per 1,000 population, but in 1966 the API rate
was only 2.2 per 1,000 population (Table 5.5). Donor
assistance ended during 1968-1972 and malaria death rose in
the following years indicating the difficulty of malaria
control in Thailand. Unfortunately, it cannot be stated
that a rise in incidence naturally followed these events,
since the data on malaria incidence during 1966-1971 are
incomplete. Nevertheless, API rates of 3.6 in 1972 to 6.6
per 1,000 population in 1974, showed yearly increase in
malaria incidence. In other words, changing rates
increased as high as 50 percent in 1974. Figure 5.8 and

Figure 5.9 show malaria incidence rates and the percentage

annual fluctuation.

63

From 1975-1979, malaria incidence showed a fluctuating
trend, and at the same time the API appeared to stabilize
at the rates of 7.1 to 7.8 per 1,000 population. By 1980-
1982, a new peak of malaria incidence was also observed,
beginning with the API rates of 8.9 in 1980 and peaking to
10.6 and 10.1 per 1,000 population in 1981 and 1982. The
1981 peak not only shows an increase in the intensity of
incidence of malaria, but also an increase in the number
of areas affected, especially areas from the very low API
category (0-10.0) up to the next low API level with rates
of 10.1-30.0. For instance, in 1979, there was only one
province that had the highest API rates, 92 per 1,000
population, but the peak in 1980 intensified the API rates
up to 192 per 1,000 population. Additionally, in 1980,
areas with low API rates covered only 11 provinces, but in
1981, it fluctuated to include 21 provinces (also see
Figure 5.13 and Table A1).

Again, after the 1981-1982 peak, malaria incidence
continued to present a fluctuating pattern; it showed a
downward trend until 1986, but increased during the two
years, 1987 and 1988 with the API rates of 6.09 and 6.81
per 1,000 population. One plausible explanation of the
decline in malaria morbidity during 1983-1986 may be the
increase in the quantity and quality of malaria clinics and
Village Voluntary Malaria Collaborators (VCC). Malaria

clinics not only increased in numbers from 174 in 1979 to

64

475 at present, but also extended their services to
locations in high transmission areas, marketing centers,
and on migratory routes (Malikul, 1988). Table 5.6
presents the number of VCC that increased yearly from 1981-
1984. Both schemes, additional malaria clinics and
additional VCC, provided intensive prevention, early
diagnosis, and treatment (USAID, 1983) which may have
contributed to the decrease in malaria cases in those
years.

The situation of malaria in Thailand presented so far
by morbidity rates compared to the steadily downward trend
of mortality rates, reflects the fluctuating trend of
incidence. It suggests that malaria is no longer the fatal
disease it once was; however, its incidence rates remain
consistently high, with API rates of 6.8 per 1,000
population in 1988 compared to 7.8 in 1978 and 5.7 per
1,000 population in 1983 which is the lowest rate of

decrease (43.6 percent) over the twenty year period of this

study.

65

Table 5.5 Malaria Morbidity Rates in Thailand, 1972-1988
(API Rates per 1,000 Population).

 

 

Year API Rates Rate of Change
1947 286 Pre-DDT

49 NA DDT operated
1966 2.2

68 NA Donor assistance ended
1972 3.6

73 4.4 22.2

74 6.6 50.2

75 7.4 12.1

76 7.2 - 2.7

77 7.7 6.9

78 7.8 1.3

79 7.1 - 7.0
1980 8.9 +25.4

81 10.6 +19.1

82 10.1 - 5.0

83 5.7 -43.6

84 6.1 + 7.4

85 5.6 - 8.0

86 5.1 - 9.2

87 6.1 +19.2

88 6.8 +11.8

 

Source: Annual Report, Malaria Division Report, Ministry
of Public Health, Thailand.

Mote. (1) Calculated from the above data.
NA = Information not available.

Table 5.6 Number of Village Voluntary Malaria
Collaborators in Thailand: 1981-1983.

 

Working Volunteers

 

 

Year Total Volunteers No. Percentage
1981 33,085 14,154 42.8
1982 33,278 21,272 63.9
1983 32,432 21,514 66.0

 

Source: Malaria Division, Ministry of Public Health,
Thailand.

30-“D—C'DO'D OOO- d\.."lr -13)

ens-=0 onu-aoo~ov -uca:)

66

12"

10"

 

 

0 x

I I I r I I I

1972 73 74 75 76 77 78 79 80 81

Year

I I I I I T I

82 83 84 85 86 87 88

Figure 5.8 Malaria Morbidity Rates.
Thailand: 1 972-1988.

60'-

4o—
20-
/\
V \/

 

A /\

L/

 

'60 I I I F I I I I
1973 74 75 76 77 78 79 80 81
Year

I fi I I . I I

82 83 84 85 86 87 88

Figure 5.9 Annual Percentage Change in
Malaria Morbidity. Thailand: 1973-1988.

67

Malaria incidence trends also show that climatic
conditions and topographic features determine the ecology
of both human host and vector hosts, and their contacts.
Many studies have shown that the ideal temperature range
for mosquito activity, breeding, and transmission of the
parasite is 68 0F to 86 oF (20 °C to 30 0C). High
relative humidity, over 60 percent, affects the life span
of the mosquito and its activity. The worst period for
mosquito breeding and intensification of the biting
cycle of Anppnelee is during the rainy season and a few
week afterwards. Thus, in some areas the greatest
incidence of malaria occurs during the late portion of
the rainy season and immediately afterwards (Dutta and
Dutt, 1978).

Malaria in Thailand has a clear time-seasonal
occurrence. The average monthly incidence of malaria
during 1985-1988, indicates that the lowest rates occurred
in the months between January and May with API rates
ranging from 3.3 to 5.5 per 10,000 population. The highest
malaria incidence occurred at two different times, during
June and July with API rates of 6.4 and 6.1 per 10,000
population: the other period of high incidence was December
with API rate of 5.8 per 10,000 population. The density of
mosquitoes during the rainy season which, in Thailand,

begins in mid May and the first few weeks thereafter,

68

probably more than any other factor, determines the rate
of malaria transmission. Anopheline mosquitoes are most
common in the period of June and July which is the time
for enhanced breeding places, and breeding and biting
cycles.

The average monthly malaria incidence from 1985 to-
1988 and climatological data from 1956 to 1988 are
summarized in Table 5.7. The greatest malaria incidence in
Thailand occurs when the optimum temperatures are between
82-83 0F with relative humidity of 78%, and rainfall ranges
from 7.4 to 8 inches per month. That is a few weeks after
rainfall, and when conditions are warmer and more moist
(see Figure 5.10 to Figure 5.12). The relationship between
the climatic pattern and accentuated malaria incidence in
Thailand and India are similar. In Trichy, India, a high
incidence of malaria occurs in September and December when
there are ideal temperatures, relatively high humidity, and
large amount of rainfall (Dutta and Dutt, 1978).

However, in Thailand, there is a slight variation from
the above pattern. The other period of high malaria
incidence occurred in December with an API rate of 5.8 per
10,000 population. Climatic conditions in this period show
a mean temperature of 75.6 0F with relative humidity of
71.9%, and a moderate amount of rainfall of 4.1 inches.
Additional data showing the monthly high incidence of

malaria among provinces between 1987 and 1988, is presented

69

in Table 5.8. The highest incidence was found in December
in Trat (62), which has been in the highest rank since
1979, followed by Chanthaburi (63) usually in the second or
third highest rank (also see Table A1 and A2 in Appendix
A). In 1988, Trat (62) had 5,081 positive reported cases
in December compared to 2,635 cases in May. Similarly,l
Chanthaburi (63) had 3,556 positive reported cases in
December compared to 3,071 cases in June. The same pattern
of this high incidence of malaria in December was repeated
in 1985 and 1986 rather than the period of June and July.
Entomological study by the Malaria Division supports the
results. The study indicates that in the Southeast section
bordering Kampuchea, the transmission density of A. gipne
exceeds that of A. minimus. Their transmissions are
highest in two seasonal periods, beginning in the rainy
season (June) and the end of the rainy season (November).
The high intensity of transmission in Thailand
produces two seasonal peaks of malaria incidence. The
first peak of incidence is in June and July, immediately
after the rainy season, and generally seems to be prevalent
throughout the country. The second peak prevails in
December and it is more likely to be prevalent in the

Southeast region.

70

Table 5.7 The Average Monthly Malaria Morbidity Rates
and Climatic Conditions in Thailand: 1985-1988.

 

(1) (2) (3) (4)

 

API Rates/ Mean Relative Rainfall
Month 10,000 Temperature Humidity

Population ( F) ( %) (inch.)
Jan 4.33 76.7 67.3 1.1
Feb. 3.52 79.7 68.7 0.9
Mar 3.49 83.2 65.5 1.1
Apr 3.27 85.0 69.3 3.5
May 4.86 84.3 76.9 8.3
Jun 6.39 83.5 78.3 7.9
Jul 6.08 82.8 78.2 7.4
Aug 5.54 82.5 80.2 9.8
Sep 5.14 81.7 82.0 10.8
Oct 5.42 80.9 81.7 8.2
NOV 5.43 78.8 77.3 5.9
Dec 5.75 75.6 71.9 4.1

 

Mppe. (1) Calculated from monthly malaria record,
Malaria Division, Ministry of Public Health,
Thailand.
(2-4) Adapted from climatological data of Thailand
30 year period (1956-1985) and monthly record
of year 1986-1988, Meteorological Department,
Ministry of Communication, Thailand.

71

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Table 5.8 Number of Reported Positive Cases of Malaria by
- Month in Selected Provinces, Thailand: 1987,1988.
Month (1987)
Provinces .
Jan Feb .Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Sougngastern Region
(62) 1453 1339 1165 1209 1689 2210 1520 1030 799 788 1272 1756
(63) 2690 1832 1733 1292 1954 2605 2313 2075 1581 1702 2430 2803
(54) 1058 703 815 637 743 1487 1822 1743 1660 1221 1594 1533
Northwestern Region
(15) 850 729 343 352 729 906 812 1015 699 529 821 931
(1) 2549 1992 1553 1150 2342 2859 2538 3149 2890 2444 3144 3174
(56) 1039 768 725 578 1272 2200 2398 1678 1165 1452 1832 1910
Southern Region
(38) 370 338 643 559 971 997 1166 629 573 511 510 438
(42) 207 224 268 309 793 1906 2145 2041 1721 2275 1888 1491
(47) 1583 1148 1226 1129 1562 1608 1286 1262 693 1166 357 348
(48) 775 733 775 949 1626 3006 2647 2882 2373 2146 2187 1389
(49) 445 475 560 458 770 766 610 619 622 410 540 465
(50) 86 69 54 57 172 624 594 698 758 770 924 876
.1988
Southeastern Begign
(62) 1813 1653 2134 2396 2635 2166 1172 1021 591 1242 2139 5681
(63) 2170 2067 1571 2090 2593 3079 1784 1587 1141 1383 1841 3556
(54) 864 853 1078 977 1202 1727 1203 1237 1137 1260 1145 1134
Northwestern Region

‘ (15) 667 369 202 395 545 1023 754 682 583 722 899 738
(1) 1483 1292 1485 1242 2046 2401 2541 2774 2703 3132 2983 2158
(56) 1092 961 1442 1159 2457 2534 2404 2495 247 1858 2022 1517
Southern Region
(38) 696 1025 1032 1099 1822 1981 1791 1346 946 2006 997 740
(42) 1232 1176 1256 865 1029 898 663 754 677 1144 622 656
(47) 763 748 754 731 1626 3138 3738 3663 3219 2745 2450 1683
(48) 1073 997 991 '870 1444 1415 857 1060 611 866 337 285
(49) 294 359 332 411 511 349 230 256 287 628 364 527
(50) 948 1454 1282 1471 2307 2079 1500 1205 866 1276 500 436

 

Source: Monthly Report, Malaria Division, Ministry of Public

Health, Thailand, 1987-1988.

Note.

 

and Prachinburi (54).

Nogthwestern Region: Mae Hong Son (15), Tak (1), and

Kanchanaburi (56).
Southern Region: Yala (38), Krabi (42), Surat Thani

(47),

Provinces in parentheses are:
Southeastern Region: Trat (62), Chantaburi (63),

chumphon (48), Ranong (49), and Trang (50).

73

Qggggapnic Patterns of Malaria

A continued decline in malaria death does not indicate
that maintenance and control measures should be discarded
or relaxed, since the problem of continuing incidence can
be seen in public health figures throughout the country.
Variations of malaria incidence during 1977-1988 are
illustrated in the accompanying set of maps shown in Figure
5.13 to Figure 5.16. On the map, five categories are
assigned as indicated on p. 32. An overview of the map
reveals some general incidence patterns. Most areas of
very low incidence are generally scattered throughout the
Central Plain and in the Northeast. Zones of highest
malaria incidence lie in three geographical regions: the

Southeast, the Northwest, and the South.

Areas of nighest Ingigence

The zones of highest endemic malaria incidence in the
three regions has remained relatively constant during the
time of this study, 1977-1988 (Figure 5.13 and also see
Figure BB in Appendix B). The Southeast region of Thailand
ranks highest in incidence, yearly since 1980. This is
seen especially in Trat (62) with an API rate ranging from
110 in 1982 to 202 per 1,000 population in 1983:
Chanthaburi (63) ranked as either second or third for
malaria from 1977-1987, but dropped to fourth rank in 1988

(see Appendix A1 and A2). Chanthaburi's API rate ranged

74

from 57 in 1986 to 119 per 1,000 population in 1981.

Tak (1), geographically, classified as northwest, but
administratively classified as north, ranked second highest
in the incidence rate. Tak (1)’s API rates ranged from 69
in 1988 to 100 per 1,000 population in 1984. An additional
province in this region, Mae Hong Son (15) had a moderately
high incidence in 1987 and 1988, with an API rate of 53 and
47 respectively per 1,000 population. The southern region,
comparatively, has the third highest incidence. Malaria
incidence within this region is unpredictable, yet the
overall rates remain consistently high when compared to the
other regions. Highly affected provinces in this region
vary. Ranong (49) and Yala (38) appeared to stabilize with
high incidence rates since 1978. Ranong (49), on the east
coast of the peninsula, worse in 1979 with an API rate of
92 per 1,000 population: and in 1988 its API rate was 45
per 1,000 population. Yala (38) on the southern tip of the
peninsula, had an API rate as high as 114 in 1980, dropped
to the low category between 1985-1987, and increased to
moderately high level again in 1988. Krabi (42) had the
highest category in 1988 after experiencing previous high

rates in the years 1979-1982.

75

 

 

 

 

 

 

 

API Rates
Per 1,000 Population
0.0-10.o Very Low
10.1-30.0 7/ 10"
30.1-50.0 CZ”? Medium
50.1-70.0 \./v Medium High
70.1-202.3 High

Figure 5.13 Malaria Morbidity in Thailand, 1977-1988.
Annual Parasite Incidence Rates, by Province.

Source: Annual Report, Malaria Division, Ministry of Public Health,

Thailand, 1977-1988.

76

 

 

 

APIluMas
Per 1,000 Population

0.0-10.0 Vary Low
10.1-30.0 C/ Low
30.1-50.0 72% Iodin-
50.1-70.0 é . Mediun High

Figure 5.14 Malaria Morbidity in Thailand, Peak Years
(1981,1982) Versus Recent Years (1987,1988)
Annual Parasite Incidence Rates, by province.

Source: Annual Report, Malaria Division, Ministry of Public Health,
Thailand, 1981,1982 and 1987,1988.

 

 

 

 

 

 

77

 

 

caW'
fiaifl

aaé

1982

 

 

’7 )' "'
/ :gfluzy

. a’lz

1987

 

API Rates
per 1,000 Popualtion

 

0.0-10.0 Very Low
10.1-30.0 (7" Low

/ /
30.1-50.0 'CZQ Medium
50.1-70.0 xy.‘ Medium High
70.1-202.3 High

Figure 5.15 Malaria Morbidity in the Southeast and
the South of Thailand, Peak Years (1981,1982)
Versus Recent Years (1987,1988).
Annual Parasite Incidence Rates, by Province.

Source: Annual Report, Malaria Division, Ministry of Public Health,
Thailand, 1981,1982 and 1987,1988.

 

 

 

 

 

 

 

 

78

 

 

 

 

 

API Rates per
1,000 Population

 

0.0-10.0 Very Low

70 . 1-202 . 3 High

 

 

 

\\‘ \\

 

 

 

\
XX‘xx \ \

>

 

Figure 5.16 Malaria Morbidity in the Northwest of
Thailand, Peak Years (1981,1982) Versus Recent
Years (1987,1988)
Annual Parasite Incidence Rates, by Province.
Source: Annual Report, Malaria Division, Ministry of Public Health,
Thailand, 1981,1982 and 1987,1988.

79

Factors Contributing to High Malaria Rates

‘The following discussion seeks to correlate malaria
incidence in three regions with certain associations of
topographical, environmental, socioeconomic, and cultural
factors.

The three regions with the highest incidence of
malaria have some characteristics in common, in addition to
their own specific problems. The Tropical Monsoon Climate
of the Southeast, the Northwest, and the South brings about
luxuriant and valuable tropical evergreen rain forest so
common in these areas. Anopheline mosquitoes live in
varying environmental habitats and in particular the rain
forests. These three rain forest regions have indigenous
hyperendemic malaria or "jungle disease" as malaria is
commonly known in Thailand. The rich tropical forest
contains a diversity of commercially viable forms and
species of plants. In addition, the South and the
Southeast are also rich in the production of cash crops
such as rubber and tropical fruits. Coffee is in the
South, and sugar cane and maize in both the Southeast and
the West regions. Moreover, the geological structure of
these three regions provides a wealth of mineral resources
such as tin, gypsum, monazite in the South, and gemstone in
both of the Southeast and West Mountain Range.

Agricultural land-use and mineral extraction attract

populations who desire a relatively high standard of living

80

available through employment in these areas. It is notable
that since 1982-1987 the export of rubber and of precious
stones has increased yearly. For example, the exported
value of rubber rose from 9,490 in 1982 to 20,539 million
Baht in 1987: and the exported value of precious stones
rose from 4,671 in 1982 to 11,550 million Baht in 1987
(EIU, 1988).

Many factors affect the intensity and geographic
extension of malaria in Thailand. The socioeconomic
development projects of the country, such as the
construction of roads and dams for irrigation and
generating electricity, are factors that favorably alter
both the topographical and the ecological Conditions for
breeding and spread of mosquitoes, as well as the
population's exposure to them. Boonag, Sornmani,
Pinichpongse, and Harinasuta, (1979) revealed that in 1978,
the increase in malaria prevalence rates in two remote
villages near the construction dam site in Kanchanaburi
(56), resulted from ecological changes favoring Anopheline
mosquitoes.

Occupational migration is an important factor that
alters biological factors which affect the transmission of
malaria. Increased population density in high risk areas
increases the probability of exposure, while migratory
populations increase the probability of infected carriers

resettling in low risk areas. In Thailand, certain areas

81

with low agricultural productivity cannot offer full
employment to the local farmer, particularly in the
Northeast region. Thus economic pressure forces large
numbers to migrate in order to earn a living wage. A
portion of immigrants from adjacent provinces and other
parts of the country sought jobs in the development
projects, such as the Phumiphon Dam in Tak (1),
Srinagarine Dam in Kanchanaburi (56), and Bang Lang Dam in
Yala (38). These workers were usually seasonal laborers in
sugar cane plantations in Trat (62), Chanthaburi (63), and
Kanchanaburi (56), or rubber tappers and coffee plantation
workers in southern provinces. They also found employment
as ore-diggers, gem miners, charcoal makers, or loggers.
The study of "Internal Migration in Thailand, 1970-
1980" by region of previous residence, age group and sex
(Piampiti, 1985) showed that immigrants to the provinces of
Trat (62), Chanthaburi (63), Tak (l), Kanchanaburi (56),
Ranong (49), and Yala (38) were predominantly male. The
number of males aged 20-39 and females aged 20-24 were
greater than other age groups. " Immigrants" referred to a
population who moved around in the province, as well as
those who moved from other provinces. Out of ten reasons
given for by males migrating, the most common (20 to
48 percent) was to seek work (see Table A3 in Appendix A).
As for females, the first reason for moving was to maintain

the family, and the second reason was to look for work (15

82

to 27 percent). The in-migrants, who move within the
province, also has the same percentages and reasons for
migration. In some of the development projects in the
country, only 33 percent are local residences, the rest are
from other places (Kondrashin, 1986). About half of the
population in Mae Sariang, a district of Mae Hong Son
Province (15) in the Northwest, were lifetime labor
migrants. Male migrants of 20-79 years were more numerous
than females (Kunstadter, 1983). Pinichpongse and
Doberstyn (1986) mapped the population movement in and out
of each region of Thailand. The results revealed that the
majority of migrants were seasonal and temporary workers
who worked in Chanthaburi (63), Trat (62), provinces near
the Kampuchean border, certain areas of the North,
Northeast, and in parts of the Burmese border.

The arrival of newcomers from low risk areas to the
hyperendemic malarial areas could, as a consequence,
contribute to a higher rate of malaria. These migrants may
be employed to work in the foothill forest fringe areas
which have endemic malaria. In this situation, the migrant
workers are more accessible to the vectors because of poor
housing and working conditions. They may live in temporary
shelters, open-wall huts, or simply out-of-doors without
mosquito nets or screens. Findings from a study of
"Interaction Effects of Socioeconomic Factors Influencing

Malaria Occurrence in Trat" (62), revealed that frequent

83

circular movement into the forest was the most significant
risk factor in this area (Butraporn, Sornmani, and
Hansapreuk, 1986). They also found that people living near
the forest and vector breeding streams were susceptible to
malaria. Studies of morbidity of the laborers in
Kanchanaburi (56) suggested that the migrants or newcomers
were at higher risk for malaria than the local population
(Kanjanapan, 1983: Sornmani, Butraporn, Fungladda,
Okanurak, and Dissapongsa, 1983). In addition, the
movement of local villagers into the forest for woodcutting
and to expand their cultivation has also contributed to a
significant increase in morbidity (Prasittisuk, 1986).
Svetsreni (1982) observed that illegal digging for ore in
the forest fringe areas of the western Thailand, often left
open pits that became breeding sites for A. ninimus.
Moreover, some workers, engaged in legal or illegal
economic activities, worked at night which appeared to
contribute to a high malaria incidence. A study of malaria
transmission in northern Thai villages, found that illegal
economic activities did, in fact, result in a higher
incidence of malaria (Singhanetra—Renard, 1986). For
example, the production and shipment of timber, ore, and
foodstuffs illegally exported and imported to avoid tax
payments are carried on at night when the mosquitoes are
most active. These workers who engage in illegal

activities, also avoid check points on returning where

84

screening for fever could be carried out. Thus they often
do not receive prompt treatment. Other reasons for delay
in treatment are because they want to make a specific
amount of income before they return home for possible
treatment and convalescence. Therefore, they are
responsible, in part, for transmitting infection from both
controlled and noncontrolled areas. All night-time workers
are not engaged in illegal activities; however, they are at
higher risk of malaria in endemic areas.

Regular international migrants who are traders or
laborers cross border zones at Mae Hong Son (15), Tak (1),
Kanchanaburi (56) in the Northwest, Ranong (49) and Krabi
(42) in the South, bordering Burma, Trat (62), Chanthaburi
(63), and Prachinburi(54), in the Southeast bordering
Kampuchea, and thus cause increased transmission of the
disease. These migrants contribute to a significant
increase in malaria morbidity, and they distribute a strain
of 2. falcinarum which is highly resistant to prophylactic
drugs (Prasittisuk, 1985). Vendrager (1986) pointed out
that the development of malaria which is resistant to drugs
in Pailin, a village on the Kampuchea-Thai border, has
‘ spread to neighboring countries. Pailin is the center of a
continuous and intense population movement of Kampuchean,
Chinese, Vietnamese, Burmese, and Thai inhabitants. Pailin
offers employment due to its precious stone mines. This

inflow of migrants has a double negative effect on malaria

85

by increasing the gametocyte reservoir and vector density.
Surface mining activities leave depressions where water
accumulates, thus providing additional mosquito breeding
areas. These migratory people are also carriers infected
with a multi-drug resistant parasite. This presents
problems in terms of ongoing and follow up care. Malaria
clinics screening Thai gem miners, who have been
prospecting across the border into Kampuchea, usually find
that 40 percent of all those screened are positive for P.
falciparum (Pinichpongse and Doberstyn, 1983).

In 1987 the Malaria Division Report indicated that Tak
(1), Mae Hong Son (15), Trat (62), and Chanthaburi (63)
were confronting a high percentage of P. falciparum along
with a high degree of drug resistance (Prasittisuk, 1988).
Pinichpongse et al., (1982), observed that since 1978, true
resistance of g.falciparun to sulfadoxine-pyrimethamince
was found in people who have contracted malaria in these
localities. Low cure rates of only 32 percent were found
in Thai patients living close to the Kampuchean border, 39
percent in the Northeast, and 42 percent in the West of the
country. Resistance of P. falciparum to the sulfadoxine-
pyrimethamine along the Kampuchean border was confirmed
following the influx of Kampuchea refugees in 1980
(Hurwitz et al., 1981). The continuous movement of
population spreads the drug-resistant strain to other

receptive parts of Thailand and its neighbors. The new

86

focus of drug resistance to the parasite, carried by
migrant workers, also spreads to north Malaysia, east
Malaysia, to Borneo and to the Philippines.

International refugee flight as a result of political
conflict among Thai’s neighbors tends to increase the
problem of high malaria incidence. Control of the disease
proves difficult for Thai public health authorities
especially in the provinces near the borders of Burma and
Kampuchea. Internal strife in Kampuchea since 1979 which
worsened in 1980, impelled the Khmers to migrate to the
border region of Kampuchea and Thailand. These refugees
lived in the camps which sometimes were temporarily
evacuated into Thailand as a result of dry-season fighting
on the border. It is notable that malaria incidence in
Prachinburi (54), an area which experiences acute
crossborder tension, rose from a low level API rate of 12.9
in 1979 to 28.7 in 1981, and moved into a medium category,
34.4 per 1,000 population, in 1982 (see Figure 5.16). Meek
(1986) studied malaria epidemiology in different camps,
from 1983-1985, and found that malaria incidence among
these people began to increase in June and July reaching a
peak in October to November. It is noted that the malaria
incidence in Trat (62) and Chanthaburi (63), the first and
second highest incidence of malaria in Thailand, had their
second peak in December. Additionally, three out of eight

refugee camps are located in Trat (62). Another receptive

87

border area with international migration as a result of
political conflict, is in the Northwest, bordering Burma.
Remote mountainous areas along the Thai-Burma border,
particularly before the rainy season, are often the hiding
places for Karen peoples, a large ethnic group who oppose
the Burmese government. These remote malarial areas are
often beyond the reach of Burmese or Thai government
services.

Mosquito vector resistance to DDT insecticide and
the population’s objection to DDT spraying of their
houses are other factors responsible for the consistently
high malaria incidence in Thailand. Presently, the three
mosquito vectors, A. gigng, A. minimus, and A.
maculgtus, are all known to be highly exophagic and
exophilic. But, prior to DDT spraying these mosquitoes
used to bite their victims within doors and remain
indoors to digest the meal. After DDT spraying became
customary, the mosquito came indoors only to obtain its
blood meal and then returned to the-out-of-doors.
Mosquitoes seek victims out-of-doors as well as within,
but theychanged their behavior to digest the meal out-

‘ of-doors, free from DDT contamination. Accordingly,
although entomological studies show that in many areas in
Thailand, Anopheles is still susceptible to DDT, it seems
likely that residual house spraying of DDT or any other

insecticide will become less capable of achieving

88

effective control (USAID, 1981: Prasittisuk, 1985).
Furthermore, other insecticides such as fenithotrion, is
more expensive and lasts for a shorter time, requiring
more frequent applications. Hence, DDT is still used in
Thailand, though people feel DDT has an immense negative
effect on human health and is a hazard to the young and
very old, as well as their domestic animals (USAID, 1981:
Hongvivatana et al., 1985). There is widespread
opposition to DDT house spraying. In Thailand,
population in sprayed areas complain of DDT’s smell, as
well as the residual damage to their iron roofs, internal
compounds and household furniture.

Statistics show that resistance to household spraying
continues to be a problem. Table 5.9 presents the result
of spraying operations. The national average of completely
spray coverage of houses from 1973-1987 was between 40 to
mid 60 percent. It is believed that less than 60 percent
coverage will not stop transmission of the disease (Malaria
Division, 1983). This problem is serious in some areas of
the southern provinces, Yala (38), Pattani (41), and
Narathiwat (39) where the majority of the population is
'Moslem and use Yawi language. In Yala(38), an area of the
highest malaria incidence, 80 percent of the population is
Moslem. They live in villages as opposed to larger towns.

It is a custom of Thai Moslem not to allow spraying teams

89

to enter their houses, especially when the man of the house
is not present. Therefore, complete coverage in the south
is as low as 13 percent (USAID, 1981). In addition, the
Mid-Term Evaluation of USAID indicated that the turnover
rate of the temporary wage employees is high in the
southern region. DDT spraying is not only a difficult job,
but it also pays a low wage when compared to the income
derived from other local occupations. Probably, those two
problems are predominantly in the South. Coverage by DDT
spraying among the hill tribes is low because of problems
associated with reaching such distant, scattered
populations.

Analyses of the factors in the previous section
suggest that topographic and climatic conditions in the
tropical rain forest contribute, in part, to the incidence
of indigenous malaria in three areas, the Southeast, the
Northwest, and the South regions. Population migration
both internal and international, linked with economic
activities, also induces a higher incidence in those three
areas. International activities resulting from political
conflict among Thailand’s neighbors tends to increase
further the problem of high malaria incidence,
particularly in the Southeast and the Northwest regions.
Finally, population opposition to the DDT spraying of

houses is a problem especially in the South.

90

Table 5.9 Result of Spraying Operation-Cycle 1

 

 

Year/Coverage 1976 1977 1978 1984 1985 1986 1987

Total Houses 1084 1030 996 526 449 477 402
(Thousand)

% Completely 41.3 40.3 42.9 65.2 62.9 61.8 60.3
Spray

% Incompletely 46.6 48.5 46.4 27.4 29.8 30.3 32.2
Spray

% Unsprayed 12.8 11.3 10.7 7.4 7.3 7.9 7.5

Result of Spraying Operation-Cycle 2

Total Houses 374 434 400 194 256 222 243
(Thousand)

% Completely NA NA NA 66.0 64.6 62.0 61.4
Spray

% Incompletely NA NA NA 26.2 28 29.9 31.1
Spray

% Unsprayed NA NA NA 7.9 7.4 8.0 7.5

 

Source: Malaria Division, Ministry of Public Health,

Thailand.
Nans-

NA = Information not available.

91

Other Susceptible and Prospective Malarial Areas

The goal of the Government Anti-Malaria Program (see
P. 44 above), is "to reduce the morbidity cause of malaria
in control areas to less than 12 per 1,000 population and
to prevent the reintroduction and transmission of malaria
in eradication areas by having not more than one indigenous
case per 10,000 population." (Pinichpongse, 1984). In
addition, for this study, the API rates from 1977-1988 are
used as a unit of analysis and are categorized as 0-10.0
per 1,000 population in very low level of malaria
incidence, API rates of 10.1-30.0 per 1,000 population in
low level, and so on (see P. 32 above): the following
provinces are considered to be the other prospective areas
which are susceptible to malaria incidence. Figure 5.15,
Figure 5.16, and Table A1 present the evidence of the
following findings. In the Southeast region, Prachinburi
(54) is the most susceptible area. Although Prachinburi
(54) was once in a moderately high incidence area in 1982
with an API rate of 34.4 per 1,000 population, since then
it has moved into the low category with the API rates

ranging from 17 to 19 per 1,000 population. Another

interesting province in this region is Chachoengsao (53),
which has malaria incidence in the very low level, even in
1981 and 1982 during national peaks of malaria. This
province used to be in eradication areas: however, it has

moved from a very low to low category, with the API rate of

92

11.5 per 1,000 population since 1987. It is observed that
in 1986 the arrival of immigrants to this province
increased more than two and a half times in comparison to
1970-1980 and 1984 (see Table A3 and A4 in Appendix A)).
Yet, this observation lacks information as to why these
people moved, where they lived in Chacheongsao (53), what
kind of jobs they held, whether their jobs related to
endemic areas, and what particular factors contributed to
an increase in malaria incidence in this province. Thus,
further study is needed. Kanchanaburi (56), in the Western
region, was regarded as having a high malaria incidence and
is now regarded as a control area. Kanchanaburi, since
1977-1987, is defined as falling within the low category
since 1977-1987, with API rates ranging from 14 in 1980 to
28.7 per 1,000 population in 1982. However, in 1988, the
API rate has moved to a higher category, 36.2 per 1,000
population. This province should also be closely
monitored. Chumphon (48) is another susceptible area in
the South region. It has had a moderately high incidence
during 1980 and 1981 and, continues to present the same
high pattern from 1986 to 1988. Surat Thani (47) was in
'the very low and low category during 1979-1986. It
increased to moderately high incidence in 1987 with an API
rate of 30.5 per 1,000 population and decreased to 27.4 per
1,000 population in 1988. Another prospective malarial

site for high incidence in the South is Trang(50). For

93

years, Trang (50) has not presented a high level of
incidence, except for the two years during the national
high increase of malaria. The first year that Trang (50)
reached the moderately high incidence level, with an API
rate of 35.3 per 1,000 population was 1988.

In summary, prospective provinces of malaria incidence
that should be monitored are Chachoengsao (53) in the
Southeast, Prachinburi (54) in the Northwest, and Chumphon

(48) and Trang (50) in the South.

Chapter 6

Conclusions and Recommendations

This study examines the trends of malaria mortality
rates in Thailand between 1943-1986, as well as the
demographic characteristics of afflicted groups. In
addition, this study investigates the trends of malaria
morbidity rates between 1972-1988, and seasonal climatic
conditions of malaria occurrence during 1985-1988, and

geographical patterns and influences relevant to the

incidence.

Conclusions

The findings show steadily downward trends of malaria
mortality rates since 1949 except in 1971, 1973, 1974, and
1981. In 1949, the malaria death rate was 205.5, dropping
to 183.1 in 1950, 169.1 in 1951, and 10.1 per 100,000
population in 1970. The significant decline in malaria
death rates during the period of 1949 to 1970 is generally
regarded as a consequence of using DDT, together with
increasing malaria surveillance for early detection of
cases. During the 19505 and 19605 economic development of
the country increased in tandem with this steady decline of
malaria death during the successful DDT campaigns. The use
of modern technology after World War II and the investment

in infrastructure in many parts of the country improved the

94

95

overall health and sanitation of Thai people. The Thai
economy enjoyed a growth rate average of 4.7 percent
annually between 1951 and 1958 and 8.6 percent between 1959
and 1969, dropping in the early 19705: the first peak of
malaria death began in 1971. Speculation suggests that
malaria resurgence in 1971 was due to the reduction of
insecticide use, in connection with a withdrawal of
financial support from the international community during
1968-1972. The increasing rate was 23.8 in 1971, 25.7 in
1973 and 11.3 percent in 1974. In addition, the increase
in malaria deaths was probably associated with the
political unrest in Kampuchea, Vietnam, and Laos, which
ended in 1975. Infected persons, military personnel,
traders, and others involved in this region, may have
contributed to the spread of malaria.

Despite a steady decline in malaria death from the mid
19705 to 1980, a second peak was observed in 1981. This
increase was 6.2 percent, approximately 1-2 fold less than
the first peak (1971). The new rise of malaria death is
attributed mainly to populations moving to live and work in
mosquito-infested transmission areas. Since 1982-1986
malaria mortality rates dropped each year from 7.8 in 1982
to 2.9 per 100,000 population in 1986. The effectiveness
of medical care possibly coupled with the shifting of the
labor force, from the agricultural sector to other sectors,

contributed to fewer malaria deaths in those years.

96

Demographically, the worst afflicted group comprised
males working-age of 15-24 years, as well as an increased
rate in the 25-34 year group.. Probably, males spent a
greater time working outdoors. The more time they spent
outdoors exposed to mosquitoes, the more vulnerable they
were to malaria infection. In addition, males had a
tendency to delay seeking medical care, since they did not
want to lose their daily income. This behavior enhanced
the possibility of more frequent severe illness and death.

Malaria morbidity rates, indicated by annual parasite
incidence rates (API) per 1,000 population, show a
fluctuating trend compared to the steady decline in the
rates of mortality. The API appeared to stabilize at a
rates of 7.1 to 7.8 per 1,000 population during 1975-1979,
and peaked to 10.6 and 10.1 per 1,000 population in 1981
and 1982. This peak not only reflects higher incidence
rates, but also an increase in the number of affected
geographical areas. Following the 1981-1982’s peak, the
API rates decreased until 1986. Increases in the number of
malaria clinics, Voluntary Malaria Collaborators (VCC), and
extension of the services to locations in high transmission
'areas provided the intensive prevention, early diagnosis,
and treatment which contributed to the decrease in malaria
cases in those years (Prasittisuk, 1985). However, by

1987-1988, the incidence rates rose with API rates of 6.1

97

and 6.8 per 1,000 population compared to 5.1 per 1,000
population in 1986.

The average monthly incidence rates from 1985-1988 and
the long term climatological data from 1956-1988, indicated
that the greatest number of malaria incidence rates
occurred in June and July with the API rates of 6 per
10,000 population, and in December with the API rate of 5.7
per 10,000 population. It is apparent that the first
incidence peak onsets are the few weeks after the rainy
season accompanied by the warmer and more moist conditions.
The appropriate temperatures of both peaks are 76-83 OF
with a relative humidity of 72-78%. The incidence peak in
June and July is common throughout the country, while the
second peak in December, seems to affect more number of
cases in the Southeast.

The geographical patterns showing the highest
incidence of malaria occur in the Southeast, the Northwest,
and the South regions. The highest malaria incidence in
these three regions remained relatively constant during the
time of this study, 1977-1988. The Southeast ranks as
having the first highest malaria incidence since 1980. The
' Northwest and the South rank as the second and the third
highest malaria incidence. It is notable that provinces
having high malaria incidence, lie on the border zones with

Burma on the West and the South, and Kampuchea on the East.

Provinces having high and moderately high incidence of

98

malaria in the Southeast are Trat (63), Chanthaburi (62).
In the Northwest, Tak (1) and Mae Hong Son (15) have high
malaria incidence. In the South, high incidence areas
vary. Ranong (49) and Yala (48) appear to have stabilized
with high incidence rates. An additional province of high
incidence in the South in recent years was Krabi (42).
Prospective provinces of malaria incidence that should be
monitored are Chachoengsao (53) in the Southeast,
Prachinburi (54) in the Northwest, and Chumphon (48) and
Trang (50) in the South.

Malaria morbidity in Thailand involves a complex of
ecological, environmental, and economic factors.
Topographic and climatic conditions of the tropical rain
forest contribute, in part, to the indigenous malaria of
the three high incidence areas. Agricultural land-use,
such as rubber, coffee and sugar cane production, and
timber and mineral extraction, such as tin, gypsum, and
gemstones, attract migrant populations. The arrival of
newcomers from low risk areas to the hyperendemic malarial
area contributes to an increase of malaria. These migrant
workers are more susceptible to exposure because of poor
‘ housing and working conditions. Many houses lack mosquito
nets or screens. Workers, engaged in legal or illegal
economic activities, may work at night when mosquitoes are
most active, and they are therefore exposed to a high risk

of infective bites. International migration resulting from

99

political conflict among Thailand’s neighbors tends to
increase the problem of high malaria incidence,
particularly in the provinces on the Thai-Burma and Thai-
Kampuchea borders. Remote mountainous areas of Thai-Burma
border are often the hiding places for Karen Peoples
opposed to the Burmese government. These malarial areas
are beyond the reach of Burmese or Thai government
services. Kampuchean refugees lived in the camps which
sometimes were temporarily evacuated into Thailand as a
result of dry-season fighting on the border.

Provinces in the Southeast are known to have a high
level of parasite resistance to chloroquine. The malaria
problem also becomes more difficult to curb due to
increasing mosquito-resistance to insecticides, as well as
community objections to DDT spraying of their houses. It
is believed that less than 60 percent coverage will not
inhibit transmission of the disease: the national average
of complete spray coverage of houses from 1973 to 1987 was
between 40 to 60 percent. It has been observed that
mosquitoes changed their behavior to bite victims and then
live out-of-door, free from DDT contamination. Opposition
- to DDT spraying of households arose because populations in
spray areas disliked its smell, as well as its residual
damage to their iron roofs and household furniture. They
also believed that DDT was hazardous to the young and very

old including their domestic animals. The problem of

100

population opposition to DDT spraying is more serious in
the southern provinces where the majority of population is
Moslem. It is a custom of Thai Moslem not to allow
spraying teams to enter their houses, especially when the
man of the house is not present. Therefore, the malaria
spraying teams have difficulties to do their jobs.

With the notable exceptions of 1971, 1973, 1974, and
1981, malaria mortality rates in Thailand have steadily
declined. It is suggested that malaria is no longer the
fatal disease it once was. However, a decline in malaria
deaths does not indicate that maintenance and control
measures can be relaxed or discarded, since the incidence
rates remain dangerously high, especially, in the
Southeast, the Northwest, and the South regions, and the

prime causes of malaria are still difficult to eliminate.

Recommendations

It is apparent that the steady drop of malaria
mortality rates over 40 years reflects the effective
application of curative medicine. However, fluctuation
and consistently high malaria morbidity rates call for
- measures in preventive medicine. Emphasis should be placed
on promoting health education and community participation.
Horizontally oriented basic health service are needed. In
particular, preventive care should be intensified for

populations of working-age who live in the three high-risk

101

regions. Village voluntary malaria collaborators (VCC), who
live close to people they serve know the various activities
of their people. These volunteers would be the key persons
who provide efficient malaria prevention. VCC would
distribute presumptive medicine to their villagers having
occupations with high malaria risk before or during its
peak. Regulations should be issued for high risk
populations to take weekly suppressive antimalarial drugs
or to report to VCC if they have a fever. Simple malarial
health education should be provided to immigrants on pay—
days or on social gatherings or occasions in the village.
Regarding future studies, the influence of
socioeconomic factors and micro-environmental factors upon

malaria incidence should be carefully taken into account.

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Appendices

Appendix A

1.113

 

 

 

 

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00:30....

 

2.1.88 _.< 030..

113

Table A.2 Selected Provinces Having Annual Parasite
Incidence Rates over 10 per 1,000 Population.

 

Year
Provinces
1981 1982 1983 1984 1985 1986 1987 1988

 

 

S t 5

Trad 176.9 175.0 110.3 202.3 131.7 111.8 103.9 122.3
Chantaburi 119.1 112.1 60.0 81.6 65.5 57.7 72.6 67.4
Rayong 45.5 34.2 17.7 22.6 14.5 10.6 15.3 20.4

Prachinburi *28.8 34.4 16.6 16.2 18.3 15.7 19.1 18.0
Chacheongsao 5.5 5.7 3.0 3.1 8.2 9.1 11.6 11.5

Nopthen Regien
Mae Hong Son 13.0 17.6 12.4 13.0 17.7 30.0 53.7 47.2

Monthwespezn Pegign

Tak *89.5 87.3 49.0 100.5 99.1 82.3 79.1 69.8
Kanchanaburi 24.7 28.7 18.8 25.7 24.7 26.8 26.4 36.2
Prachuab 17.4 22.6 13.1 13.7 13.1 12.7 12.4 13.7
Kiri Khan
S u e
Ranong 85.9 71.2 51.2 37.2 31.6 45.6 70.6 44.7
Yala 89.4 73.0 47.2 67.3 21.6 20.0 25.8 45.0
Krabi 64.5 36.1 13.2 7.6 3.5 5.7 44.5 70.6
Chumphon 30.7 28.0 19.1 13.5 12.9 32.4 48.2 37.5
Trang 13.8 12.8 8.1 5.2 2.0 2.1 7.6 35.3
Phangnga * 39.8 34.2 24.0 20.0 8.5 11.2 24.4 17.9
Surat Thani 15.1 22.2 17.9 7.2 3.0 13.9 30.5 27.4
Nakhon Si 10.2 8.8 5.0 3.6 3.0 5.0 8.4 16.0
Thammarat
Pattani 13.1 18.3 12.8 15.5 5.7 6.0 5.3 11.9

 

Source: Annual Report, Malaria Division, Ministry of Public
Health, Thailand, 1981-1988.
Nope. * Prospected Provinces that should be monitored.

114

 

 

 

Table A.3 Number of Immigrants in Selected Provinces,
1970-1980.
1970-1980 Reasons for Moving*
Provinces Male Female Looking Maintain Family
for Work

Male Female Male Female
C
**BangkOk 161,125 179,667 37.4 38.9 9.8 22.7
Nonthaburi 25,619 22,120 14.3 14.3 24.9 50.0
**Chonburi 29,579 17,420 25.8 27.2 11.9 41.0
Trat 5,745 4,501 47.8 24.2 20.4 53.4
Chantaburi 11,016 9,614 40.4 26.2 26.2 52.7
Rayong 9,397 8,185 41.5 26.3 20.9 48.4
Prachinburi 16,439 10,969 26.6 17.8 24.4 61.0
Chacheongsao 7,635 6,835 27.1 14.9 24.3 51.0
Northern Pegion
**Chaingmai 16,226 13,152 21.6 15.5 18.6 42.2
Merhtyesrern Region
Mae Hong Son 1,930 1,381 29.3 16.4 17.5 54.6
Tak 5,346 4,077 30.2 19.4 22.0 57.2
Kanchanaburi 15,558 11,698 30.3 22.6 20.6 48.6
Southern Pegion
**Songkh1a 17,943 14,631 28.5 19.5 17.4 47.9
Ranong 3,328 2,718 42.2 19.6 21.9 53.4
Yala 9,838 7,998 32.7 26.5 13.9 42.8
Krabi 4,821 4,223 36.0 23.1 21.1 46.3
Chumphon 7,861 1,450 30.9 20.4 19.6 49.5
Trang 4,791 3,748 21.7 14.2 18.7 42.5
Surat Thani 9,788 7,747 30.0 18.3 19.6 43.6

 

Source:

Adapted from "Internal Migration in Thailand,

1970-1980" by Piampiti S. 1985 National Institue
of Development Administration, Bangkok, Thailand.
More. * It is the percentage distribution of migrants 5

years of age and over from other provinces.

Out

of ten reasons for moving, these two reasons are
accounted for the largest percentage.

** The major city in each particular region.

115

Table A.4 Number of Immigrants to Provinces Having High

Endemic Areas of Malaria.

 

 

Provinces 1981 1982 1983 1984 1985 1986 1987 1988

Trat 10305 10896 12674 9140 11348 14700 11897 10720
Chantaburi 21279 21730 24852 34062 30784 29122 28072 16360
Rayong 20297 22098 41850 27436 25170 33354 29115 15759
Prachinburi 36939 46329 37181 36914 56136 61792 46800 32520
Chachoengsaol3709 14846 15538 13726 26391 33795 33809 29135
Mae Hong Son 3429 3845 4725 3981 4942 7399 7546 5693
Tak 8961 10928 17473 14392 14340 16459 14778 13706
Kanchanaburi25001 31977 30974 24887 36588 34659 29428 35969
Ranong 6523 6439 7561 6690 6911 9210 5797 5783
Yala 13016 13200 17506 15440 18145 26320 24948 18497
Krabi 10464 9787 11872 8772 9367 11357 13051 12753
Chumphon 15155 15916 19564 17788 21597 25272 21048 15460
Trang 15359 14709 17132 16254 18019 21156 24622 20303
Surat Thani 24501 30094 NA 37042 39756 37916 43159 31151

 

Source: Annual Report, Ministry of Interior, Thailand,
1981-1988.
Mere. NA = Information not available.

Appendix B

116

 

 

 

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. fies-‘19.

.15 ,
‘ Y THAILAND; PHYSIOVGRAPHIC.‘.REGIQNSE

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Physiographic Regions.

 

 

Figure 81. Thailand

117

 

4’ VEGETATION
In 1le I III/I {III-

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b

 

 

     

Lowland non-seasonal loaaat
- Troplcal valnlovaal
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Figure 82. Vegetation.

118

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9 w.
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'w a a
56 ...gfl 1. 1'6): 37 1.616

70 ”w. 2. Kaapaang Phat 38. Yala
yaw J. Nakhon Savan J9. Narathiwat
. 4. Uthai Thani 40. Songkhla
68 5. Chai Mat 41. Pattani
a 6. Lap Burl. 42. Krabi
a 7. Saraburi 43. Phangnga
' a. Chaiyaphu- 44. Phukat
9. Nakhon Ratchaaiaa 45. Nakhon Si ‘l'ha-arat
\ 10. Burl ru- 46. Phattha Lung
11. Surin 47. Surat Thani
12. Si Sa lot 49. Chumphon
13. Chaim Mai 49. Ranong
14. uaphun 50. Trang
15. Mae Hong Son 51. Satun
16. Phayao 52. Chon Buri
. 17. Laapang 53. Chachoengsao
49 ' 18. Man 54. Prachin Burl
19. Phraa ‘ 55. Nakhon Mayok
20. Uttaradit 56. Kanchanaburi
21. Phitaanulok 57. Suphanhuri
22. Sukhothai 59. Ratchaburi
23. Phatchabun 59. Phatchaburi
24. Phichit 60. Prachuap nun Khan
25. Chaing Mai 61. Rayong
26. Khan Khaan 62. Trat
27. Udon Thani 63. Chanthaburi
28. Wong Dual 64. singburi
44 n 29. Sakhon Nakhon as. Angthong
50 . \ 30. Nakhon Phanoa as. Ayutthaya
31. Mukdahan 67. Saaut Prakan
J2. Kalaain 68. Bangkok
)3. Maha Sarakhan 69. Pathun Thani
‘ J4. Roi It 70. Nonthaburi
35. Ubon Ratchathanl 71. Nakhon Patho-
36. Yaaothon 72. Soul: Sakhon
73. Saaut Songkhraa

Figure B3. Provinces in Thailand.

 

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