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THS

AN EPiDEMIOLOGICAL STUDY
OF THE HELMINTH PARASITES
OF THE EnEAD-OW VOLE

'MICROTUS F. PENNSYLVAMCUS 0RD?

Thesis {or the Dagree of M. S.
MICHIGAN STATE COLLEGE

Robert Lloyd Rausch
1946}

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M-795

Date—CCU? 13

This is to eertifg that the
thesis entitled

An Epidemiological Study of the Helminth
Parasites of the Meadow Vole (Microtus 2°
Rennsylvanicus 0rd) '

presented bg

Robert Lloyd Banach

has been accepted towards fulfillment

of the requirements for

M. S. degree ingacto _arlg Public Health

; we) eat-mm
Major professor

A.-- 19%

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IIIII .Illltlll. . I‘ll-EDIIl II\-‘r. .34. I. .1»,

AH PIMIOLOGIGAL mm 01' m mum PARISH!!! 01' :33
MY VOL] (“16205118 2° mmmrcus 021))

By
some morn mean

A 931818
hunted to the School of Grant-e Studies of Itiohigan
State Golloge of Agriculture and mpliod Selene.
in partial inhalant of the requirements
fer the degree of

am 01' WING!

Department of Bacteriolog and Public Health
19116

THESIS

idmmvledment

‘i'he writer wishes to take this Opportunity to expreee hie appre-
ciation to Dr. P. 1. Mine. Dr. J. D. finer. Ir. 3. 3. “organ. Ir.
1.. a. Dice. Mr. D. Y. Kane and Dr. N. A; lotto. for their kind. eeeie-

tense. and. to the nunerone others who also contributed to eating this

work possible.

1:8?8 .91.

fable of contents

Introduction and review of literature..............1
Nethede............................................9
Reunite and dieoueeion............................10
Gonelneiene.......................................27
Refereneee oited..................................28

185100.”...o...oo.o..............................30

Ihe epideaiolog of helainth parasites hae received little etudy.
Ihie ie eepecially true of the paraeitee of wildlife. flare euch etud-
iee may contribute Inch toward the underetanding of the dynaaice of
population cyclee and other phaeee of the bionoaice of thie group of
aninale.

In the paet. noet of the work done with the helninthe of wild-
life hae been of a may nature. and it ie only lately that epidea-
iolog hae been coneidered. .ie yet. data are ineuffioient to derive
any conclueione. but with eufficient effort eone very intereeting
facte ehould be diecloeed. In the past. the work hae often not been
mied out over a long enough period of time. nor in noet caeee hae
a eufficient number of aninale been coneidered. In the caee of ani-
male with population cyclee. a etudy of coneiderable duration ie de-
eirable. in order to follow throng: at leaet one coaplete cycle.

Only one calendar year could be devoted to thie etudy. eo it ie
iqoeeible to draw any conclueione which could be applied generally
to other yeare. lhe population deneity ie undoubtedly of each iapor-
tance. but there wae not tine to etudy the paraeitee free the low point
to the peak of the cycle. It wae unfortunate that the area need for
thie work wae dieturbed by grazing and fan aanacenent practicee. iluch
care ehould be applied to the aelection of an area for euch a etudy.
and oonditione ehould be euch that the population daneity could be
carefully obeerved. It ie hoped that an opportunity will be had in
the future to continue thie work under more nearly ideal cirounetancee.

he neadow vole eeeae eepecially euited to thie type of a etudy.
since it ie widely diatributed. and can ueually be obtained in euffi-

cient numbers throth the year. There has already been accumlated
a great values of information concerning the bionoaics of this animal.
and this is of great value in attelpting to evaluate the data obtained
free such a stun as this. Since its distribution is so great. it is
found in my different types of habitat. and comparative studies would
be of interest. Since the helninths have a very definite ecological
connection with the habitat of the host. studies over widespread areas
would disclose eons interesting information. Related species. 5. £33-
313. g. m. and g. m. have received considerable study in
maps. althougx this has been aainly population studies in relation
to economic problems.

i‘here has already been done a considerable amount of work on the
parasites of rodents. Hall (1916) nonographed the nenatodee of rodents.
Harkcna. (1936) studied the parasites of north Garolina rodmte. but did
nothing with those of liicrotue. unthitt (1915) nonographed the cestodes
of the faaily Anoplocephalidee. several of which are rodent parasites.
hictson (1938) has studied the parasites of sons Iinneeota Oricetidae.
but gives little infer-etion on the parasites of Iicrotus. there are
also nunerous papers describing new species fron lorth anerican rodents.
In lit-ope a considerable anount of careful work has been done by :llton
and his associates (1931). (1912). heir work. however. as far as epi-
deniolog is concerned. has been essentially with another rodent, £129."
£92! szlvaticue. and very little with Hicrotus. According to Dr. E. a.
Baylis (1916) a sufficient nunber of paraeitee has not been found an the
other species to allow for an epidemiological study. Haailton. Blair.
Dice. Runs and others have done mch population study work with Liga-

.t_u_s_. but they give little or no information on the parasites. a number

of other workers have also contributed to the infornation available on
the bicnonics of this aniaal.

be present author bean work on the parasites of the vole in Ohio
in 19112. his was survey work only. and no effort was nade to b a sys-
tuatic study. he parasites collected from Ohio roles have proved of
considerable value in mining identifications of the specinens collected
during the course of the present problem. he naJority of the Ohio spe-
ciaens were collected in Union and liarion counties. i'o date. from all
localities. a total of well over IIOO specimens has been emined.

This problen in Iiichigan' was begun in late July of 1935 and continued.
throng: July. 19%. Oircuastances ads it necessary to select an area
near the came of lichigan State College. so a pasture field adJacent
to the Baker Ioodlot was chosen. it being the nest satisfactory in the
area.

the field selected contained about 15 acres. he vegetation was
fairly unifcrn. and consisted nainly of blue grass (:2 pratnsis L.)
with numerous plants of other kinds interspersed. Hawthorne trees (g!-
m spp.) of rather snall sise were distributed throudmut the area.
as were groups of prickly ash (Zanthoglun anericanun I»). here were
also a few areas of libernun sp. nurse saall areas were grown up with
sedges (gage; spp.). and Canada thistle (cirsiun arvense L.) was abun-
dant in sons areas. he grass around the bases of the trees nade espe-
cially favorable habitats for the voles. did there was acre protection
here against grasing. which later became a factor.

{the vegetation was fairly unifora in the beginning, and the vole
population seeaed evenly distributed over the area. but later. when

cattle and sheep were introduced. the cover was greatly radioed by gras-

ing. his was. of course. undesirable. but since no other area was avail-
able. it had to be tolerated.

l'our areas within the field were lower. and contained water at times
during the year. two of these areas. neamring about 35 by 50 feet. and
70 by 30 feet. contained alnst pure gowths of £925 spp. be larger
area. 260 by 560 feet. contained snall areas of _O_ar_g_r_ spp. interspersed
anong the blue grass. A short ditch ran across the northwest corner of
the field. but had no peculiar vegetation. nu... areas contained water
hiring the wet seasons. but were dry for the nost part (hiring the year.

An effort was nade to rsnove as nany animals per nonth as possible
without reticing the total pepulation appreciably. About 30 aniaale
per aonth were trapped. and these were taken as evenly as possible free
all parts of the field. in order to lake the remval as unifora as pos-
sible. and to prevent unnecessary pressure in any one area. kcept for
the maths of lay and July. the voles examined were all renoved from the
original area. Daring lay. through trapping for another project. an op-
portunity areas to obtain additional specdnens free a snall area of ever-
green trees i-ediately adjacent to the field on the northwest. In July.
because of an abrupt drop in the number of aninals present in the original
area. it was necessary to go outside the area in order to secure enough
roles to cleete the study.

Since there was the usual anount of inigration froa adjacent areas.
the confinement of the trapping to a limited area had no particular sig-
nificance. It was first thoudit that it night be possible to correlate
the data obtained with physicgraphic features of the field. but this was
not found to be the case. It would have been desirable to have trapped

over a larger area. since in that way a mater maber of voles would

have been obtained. is mentioned above. grazing later caused the dis-
appearance of voles froa scae parts of the field. and during Deceaber
deep snows prevented the trapping of the desired nunber.

In addition to Microtus. the short-tailed shrew (Blarina m-
29$ talpgides (dapper). the Juqing nouse (m hudsonius (him).
the prairie white-footed nouse (Peregscus _naniculatus M (Roy and
tennicott). the northern white-footed nouse (Perogscus leucopgs 322.-
boracensis (Hecher). and the house nouse (£3 msculus 1..) were trapped
in this area. A number of voles. not recorded. was destroyed partially
or wholly by the short-tailed shrew. and possibly by other voles.

rho ages of voles can be estiaated from the data given by Haailton
(1937). His figires are given as follows:

Ratio of weidit to age:

Hales
5 srm - 5 duo'-
1o - 9
15 - 12
20 - 18
25 - 2h
30 - 32
33' : :1
R5 - 66
50 - 87
,renales
5 cram - 7 dar-
1o - 12
15 - 18
20 - 2h
25 -
3'; i
go - 61
lo - 78
so - 101

In the present work. weidits only are considered. and no atteqt has

been rude to convert these to ages. It can readily be seen. however.

that in general. weiamt is directly proportional to age.

According to Hamilton (1937). growth is very rapid until the 12th
week. when it is retarded. and the animal is considered fully nature.
Bailey (19211) found that feaales nay nate at 25 days. and males aay be
fecund at ”5 days. Ve found a prenant female weiging 15 grams. so
there sust be a considerable aaount of variation in this. In any case.
reproduction takes place very rapidly airing the were aonths cf the
year.

be older aniaals seen to die during the late so.» and fall.
and only the animals born in the late suller and fall survive the win-
ter. Baker and Reason (1933) found. with g. gentle in hope. that
the aniuls die of old age about October. According to Halilton (1937)
the adult of 5. p. pmglvanicus die during the late winter. when less
than a year old. we found relatively few old voles during the winter
aonths. Dailton (1937): also lists three factors as contributive to
the short life of lucrotus: l. attainment of sexual naturity at a very
early age; 2. extreme prolificacy; 3. little cessation of activity in
search of food. According to Hamilton (1937) the length of the breed.-
ing season in the eastern United States depends upon the number of voles
present. At the low point in the cycle. the breeding period is shortened
and the litters average snaller. At the height of the cycle. reproduc-
tion occurs throughout the year. but is curtailed during the winter.
Along the voles trapped for this study. we found the last preaant fe-
Iale. with nearly full-tern feti. on lovember 5. 1n the spring. the
first evidaice of breeding in the males was noted on Hard: 6. and the
first pregnant female was taken on March 23.

According to all available evidence. the voles during this study

appeared to be near the peek of the cycle. Observations by others in
the same general part of the State sustained this opinion. According
to ID. I. Kayne (19%). the population density was the highest in this
area since 1937. his was supported by other observers ()lichigan Gon-
servaticn. 19%). Gonouses were ends at diffeer tines during the year.
following the neth cited by Dice (1938). According to this nethod.
the traps are set in a straidit line. and are assuned to draw the ani-
nals taken frcn a distance eqial to the radius of the hone range. lo
effort was nde by us to deternine the extent of the hone range. We
used the figures given by Blair (19%); he aves the hone range for the
male as 0.50 acres. and for the femle as 0.31 acres. In this way. con-
sidering the aninals trapped only (hiring the first three nights. sons
concept of the population was obtained. m means of these censuses. an
average for the whole year of 8 voles per acre was obtained. his fi-
gire is unbubtedly low. and cannot be considered accurate becmse cf the
varied conditions within the area. Considering the evidence in the
field. the animals were certainly nore numerous than the censuses would
indicate.

It was of especial interest to note that a sudden decrease in num-
ber of voles present was seen airing the latter part of June and during
m1: of 1916. low adult animals were taken during June. and later .m-
lals of all age groups becans very few in nunber. mring July it was
very difficult to obtain enough aninals. and there appeared to be a
mrked decrease over the whole general region. fittings found in the
field were few. and these were old and dry. he few renaining runways
were old and unused. Oonpared with conditions existing the previous

suslser. both on the study-area and in areas sons distance away where

no trapping had been done. the population was such decreased. more
was no evidence of any disease. and no explmaticn for this decrease
is known. althoud: it is possible that the peak of the cycle had been
passed. and the population was on the don-grade. It is to be noted
that this decrease took place before the dry weather appeared. with
a natural decrease in breeding.

Ye are indebted to Hr. D. I. Eyne. who did sons trapping con-
currently with cure. for the following information. In the conifer-
ous planting adJacent to the field in which our trapping was done.
the following meadow voles were live-trapped two or more tines. be-
tween iby l3 and by 29. 19%. and. according to Ir. Kayne presumably
were residents in this area of about one-half acre:

Adults
renales - 15

Males - 16
Ben not known - 1.

"ST

Juveniles
l'enales - 12

holes %7_
In addition. one adult and nine Juveniles were live-trapped only once.
and may not have been residents. The ninimn total population for this
area was 50 voles. 1n the neighborhood of 30 aninals was renoved by us
for examination during the last of May, but it is significant that. when

snap traps were reset during the last of July. no voles were captured in

this area.

lads

Snap muse-traps were used to capture the voles for this study.
rhese were set directly. without bait. in the runways of the anisnle.
After removal fro. the traps. the voles were taken to the laboratory.
where they were first weighed and examined for general condition.

The viscera were renoved throng; a median ventral incision. and
each organ was isolated and opened separately in a dish of water.
he contents of each viscne were emined macroscopically. and under
the low power of the dissecting nicroscope.

Any helainths recovered were placed in a dish of Ringer's solu-
tion until later. when they were fixed.

he sex of the aninals was determined definitely by enaination
of the internal organs. in order to lessen the chances of error.

0e stodes were killed in hot MI solution. and preserved in the
sine. these were later stained with Benichon's acetic carnine. and
whole aounts prepared. Sections. stained with haematoqlin-eosin.
were ads when necessary for purposes of identification.

leIatodes were killed in hot 70% alcohol. and preserved in the
sans solution. lhese were later cleared in lacto-phenol for union--

tion. lo trematodes were found during the course of this study.

10

£291“ and discussion

A total of 3115 voles was trapped and examined for this study. Of
this number. four had been partially destroyed by other animals. so
that it was not possible to obtain accurate weidits for then. coalete
data. including weidits. were available for 3141 voles.

The distribution by the nonth of voles trapped for this studv was

as follows:

“1".”"u33 “O‘Nfeeeoe lpril......32
halt...” Jam-.17....30 messeesee56
September..lh lebruary. . .29 June. . . . . . .234
ochbor....g “$000000? Ju’.......23
novubareee

!he age of the infected aninals is doubtless of Inch imortance
when considering possible nanifestations of imnolegical phenonena.
rho 3141 voles weighed can conveniently be divided into the following

weidit coups:
1. 10-15 grams
2. 16-20
a. 21-25
e 26-30
2: 31.35;
7. 1
8e “6-50

Animals falling below weidit-group l and above weidit-group 8
were so few in nunber that they are not considered (table 2). he
animals can. therefore. be separated according to the percentage of
the monthly catch falling into these 8 groups. his aonthly distri—
bution can be seen in table 1.

It is evident that during hgust and September a number of young
animals was present. but the older animals were decreasing in mater.
as would be expected if it can be accepted that the older animals die
in the 19.11. mug October and the following 6 loathe. young aninls

11

falling into the lowest weight groups are absent. since breeding has
been curtailed. Ehere is a progressive increase in the average weight
of the voles cqtured during this time. representing the normal growth
of the individuals as they become older. Toward spring the number of
older animals increases. and in by the first of the young of the year
are represented. his latter group makes up a fairly large proportion
of the catch during thy. June. and July.

the fairly even distribution of the animals in the median weight
groups during the 6 months following October is also evident from table
2. Table 3. comparing the monthly weights of the parasitised and non-
parasitised animals. also clearly indicates the absence of animals in
the lower and higher weidit groups during this period.

is shown by table 3. when there is a wide age distribution. the
average weidits of the parasitised animals are higher than those of
the non-parasitised anilmls. all species of parasites considered.

fhe following parasites were collected from voles during the course
of this study:

figstoda _
Par loce hala infre ens (Douthitt. 1915)
Tummy'o'o'gg" Lhal_a troes chi sch. 1916
gala macroc hale Douthitt. 191
Taenia taenra'efofiis (Batch. 17%

 

 

63337551.. sp.
Nematoda

hacia obvelata (kudolphi. 1802)
Fennel Efro'ia'oa Tongigpiculatus Dikmans. 19in

Proto irura sp.
W zoos vivipfius (Bloch. 1732)
base helminths are considered separately below.
2: infregens. memosis (Beer. 1927): length 20 to 75 mm;
width 1.5 to 3 am. he diameter of the soolex is OJ to 0.7 n. and

12

that of the suckers is 0.07 to 0.09 m. i'he dorso-ventral mscles are
well developed. the excretory system consists of four longitudinal ves—
sels. of which the two ventral ones are larger. and are Joined in the
posterior part of each segment by a transverse vessel. Ihs genital
pores are unilateral and the genital ducts pass on the dorsal side of
longitudinal excretory vessels and nerve. There are 50 to 80 testes
in each segment. extending laterally from the antiporal side of the
ovary. and sometimes passing the longitudinal excretory vessels on the
same side. Inch testis has a diameter of 65 to 70 microns. Ihe cirrus
pouch is piriform. 0.2 mm in length and 0.08 mm in diameter. It con-
tains a small internal seminal vesicle. and an unarmed cirrus. Ihe vae
deferens forms an external suinal vesicle before entering the cirrus
pouch. rhe vagina empties ventral to and somewhat posterior to the cir-
rus pouch. It is surrounded by glandular cells. he ovary is situated
in the poral m: of the segment. and 1. strongly lobed. 0n the ventral '
face of the ovary. an enormous seminal receptacle is found. he vitel-
1ine gland is situated on the dorsal faceof the ovary. i'he tubular
uterus extends on the ventral side past the excretory vessels. It be-
comes rapidly sacculated and. finally fills the entire sepent. he eggs
are 30 to "0 microns in diameter and contain a well developed pyriform
apparatus. '

his cestode was found to be unocnsson in the voles of this area.
with only 2f of the animls infected. In all but one case. when two
were found. this cestode was found singly in the small intestine of
the host. umally Just posterior to the stomach in the duodenum. Dout-
hitt (1915) ashes the following statement concerning the occurrence

of W variabilis. which Baer (1927) considers identical

13

with the present species. “It seems to be wholly absent from the sand-
hill regions; at BemidJi. Kinnesota. a few were found in hosts (m
bursarius) from very wet. coarse sand mixed withhimus. only a foot or
so from the edge of a swamp. In fertile soils. both uplands and hot-
toms. they vary in frequency. being in some localities extranely abun-
dant. and in others rare or apparently absentdI

his cestode was first found by us airing January. It was also
collected during rebruary and. after being absent. during larch. again
during April and lay. Its occurrence was also quite spotty in voles
previously examined in Ohio. he percentage of animals infected with
this cestode can be seen in table ’4. L11 cestodes of this species col-
lected by us had gravid proglottids.

According to the known life cycles of this group of cestodes. it
can probably be assumed that the intermediate host of this species is
a mite. Nothing is know concerning host reactions to this parasite.

a. troeschi. Diamosie: Length from "-5 to 10 . (av. 7 mm);
width 1.0 to 2.2 mm (av. 1.8 mm). Scolex 0.576 to 0.810 mm in diameter
(av. 0.710 m); 0.360 to 0.591: an long. tickers usually circular. quite
mobile; 0.360 ms in diameter. scolex nearly square on cross section;
slight grooves between suckers. deeper on dorsal and ventral sides.
Neck present. of variable length. shorter than scolex. longitudinal
excretory vessels lie in same transverse plane; they measure 0.016 and
0.013 mm; the smaller is lateral to the larger. Both excretory canals
forced ventrally by enlargement of seminal recqtacle. Iransverse canal
0.016 m in diameter. Genital pores unilateral. dextral. at about mid.-
dle of sealent; genital ducts dorsal to excretory canals. Oirrus sac
averages about 0.168 m long by 0.66 mm wide. with a central constric-

11$

tion. Internal seminal vesicle fills medial bulb of cirrus sac; latter
becomes larger than lateral bulb. Yas deferens enlarges to form exter-
nal seminal vesicle before entering cirrus sac. Cirrus spinose. fes-
tes extend from longitudinal excretory ducts to Just past aporal edge

of vitelline gland; 35 to ”0 in number. aeraging 0.0‘42 mm in diameter.
i'eetes do not extend anterior to uterus. Vagina ventral to and slightly
posterior to cirrus sac. Vagina runs medially. enlarging at level of
aporal end of cirrus sac to form seminal receptacle; latter extends
dorsally past ovary to poral edge of vitelline gland. Seminal recep-
tacle begins to fill at about middle of strobila; after reaching a
minus sise of about 0.550 by 0.235 m it decreases in sise and disap-
pears. Ovary situated at about center of proglottid. slightly poral;
lobate. Yitelline gland dorsal to ovary. with eporal edge Just poral
of mid-line. Uterus tubular. about 0.016 mm in diameter; extending
ventrally past the excretory canals. Uterus begins to fill on the poral
side about 1/3 of length from anterior end. last four or five proglot-
tids completely filled with eggs. Eggs measure from 0.030 to 0.0’40 mm;
embryo measures 0.012 an; embryo plus pyriform apparatus measures about
0.021 mm.

'm. small cestode was the most oomon found in the vole in on.
locality. 18% being infected. It occurs in the region of the ileo-cecal
Junction. and is found more co-only in the com than in the lower small
intestine. Often. when the oeoum is severed at the Junction with the
small intestine and a slight pressure applied to it. these cestodes.. if
present. were forced out the Opening. Rarely more than 3 specimens
were found in a single host. and the usual number was 1 or 2. is many
as 8 were found. however. in a single animal. It is possible that a

few of the specimens assigned to this species represent another. but

this'is unlikely. and any durum”, probably come within the range

15

of normal variation.

the 26-30 gram soigot group was most heavily infected with this
parasite (table 6). but the group preceding and the one following this
also had. a hidl percentage of infection. The average number of worms
present was about the same. regardless of age of animal (table 7). he
pod: of the number of worms presmt coincides with the peak of the in-
cidence of infection (table 5).

The hiélest incidence of infection occurred during the winter. with
the peak in December. his cestode was not found until October. and not
after the last of lay. Immature tapeworms and scolices with beginning
strobila were found rather collonly during the early part of the winter.
It was also found that immature worms occurred in larger numbers in a
single host than did the serially suture specimens. Ismature worms
were not found in the late winter and spring.

Until more can be learned. it is assumed that a mite acts as the
intermediate host of this cestode. Nothing is known of the host reac-
tion to this parasite.

g. macrocgphLla. Diaposis (Beer. 1927): The length varies from
100 to 200 mm. and the greatest width is 1.5 am. he scolex is very
large. 0.6 to 0.8 mm in diameter. and the suckers 0.3 in diameter.
Ehe ventral ducts attain a diameter of 0.32 mm. and the interproglot-
tidal enlargements of the transverse ducts attain a diameter of 0.33
mm. which represents about a third of the sealant. here are #3 to 57
testes. situated anteriorly to the antiporal side of the ovary.- and pass-
ing the excretory vessels on the same side. he testes measure about
50 microns in diameter. the vas deferens dilates into a large'external
seminal vesicle. and again. on the inside of the cirrus sac. to form
an internal seminal vesicle. There is no prostate gland. i‘he cirrus

sac is piriform. 0.16 m long and 0.08 mm in diameter. It empties into
the small genital atrium. Ihe sexual pores are unilateral. lhe vagina
empties posteriorly to the cirrus sac. It is surrounded.by glandular
cells. at the distal part. and the proximal part dilates to fonm an enor-
mous seminal receptacle. Ihe female sexual glands are situated.near the
median line. the uterus is in form of a.network situated in the anterior
half of the segment. and passing the excretory vessels laterally on the
dorsal face. he network is reduced to a single transverse tube at the
median line. lhe'uterus becomes saclike and.lobed.far back in the stro-
bila. The eggs are about 30 to 32 microns in diameter and have a piri-
form,apparatus.

Ihis cestode was found.rather commonly in the small intestine of
the vole. 12.7fi being infected. It is possible here again that a few
specimens of this genus might have represented.another species. but ma»
terial is insufficient as yet to determine this. lbr our'purpose. all
can be considered to be identical with the above.

it the most only three cestodes were found in any one heat. and
usually only one or two were present. the peak of the incidence of
infection was reached in August (table h). with a drop during the win-
ter’months. Immature specimens were again found.in the spring. suggest-
ing that the intermediate host is not available to the voles during the
winter. rhe rise in percentage of animals infected airing July. 19116.
indicates a probable peek again in August and September. here is ap-
parently no difference in age suscsptibility to this tspeworm.(tahle 8).
and no significant differences in number of worms present. according to
age (table 9). the peak in average number of worms corresponds to the

peak of incidence of infection (table 5).

1?

lith the exception of the work done on Moniesia and. cittotaenia
(Stunkard. 1937. and others) nothiu is known about the life cycle of
the cestodes of the family haplocephalidae. It probably can be as-
sumed that mites act as the intermediate hosts for the preceding three
species. It has been found (Stoll, 1935) that Moniesia infections
are able to survive at least two winters without introduction of eggs
into the area. It is generally accepted that a certain amount of mois—
ture is necessary for the well being of the mites acting as intermediate
hosts of these cestodes. .

the ecolog of the mites is undoubtedly of great importance in the
epidemiology of these cestodes. Irull (1939) found that oribatid mites.
the intermediate hosts of Quiesia. are most abundant on grass after
rather heavy rains. and. that they retained their greatest constancy
where moisture was abundant enoudl that the growth of the cans was not
inhibited. He says that the mites were not reduced excessively by pro-
longed cold wet weather of a week's duration or by a prolonged dry spell
of a month, if these changes occurred during spring and early su-ler.
lrull found that the mites were mich more abundant in spring than in
winter. He also found that they were present in very mch larger num-
bers early in the morning than during the day. he abundance of mites
on grass probably corresponds in general to the period of greatest ac.)
tivity of the voles.

It is well known that sheep acquiring Moniesia infections early in
the season will lose the tapeworms in late summer. Whether this occurs
with other anoplocephsline tapeworms is not known. Btoll (1938) showed
that this is not dependent upon the'age of the sheep.

Douthitt (1915) found tapeworms of the genera my: and EMS-2’

18

32213 in rather large numbers in 9.9932 bursarius. ins species of
the other genera of the family Lnoplocephalidae ('lbniesia. mplomha-
La. and antenna) also occur in large numbers in the host. is far
as l have been able to determine. cestodes of the genus Oittotaenia
occur in relatively small numbers in the host.

3. taeniaeformis (cysticercus). Diamosis (Bprehn. 1932): he
cysticercus consists of the scolex to which a number of segments are
attached. it the end of the strobila is found a cmdal bladder. {the
rostellum has from 26 to 52 hooks; the larger measure from O. 38 to 0J2
mm. and the smaller from 0.25 to 0.27 III. ihe asticerci are found in
cysts in the liver of numerous rodents.

the cysticerci of the cat tapeworm were found rather cononly dur-
ing the winter months. Nine percent of the animals were infected with
this parasite. he cysts. of variable size. were found in the livers
of the voles. finally only a single cyst was found in a host; in a
few cases two cysts were found. and in two cases three cysts were found.
mess were typical strobilocerci. and there can be no «pestion as to
their identity.

i'h'ese cysticerci were first found in Hovember. and during each
month thereafter until the last of May. after which none were found.
he largest number of infected animals was found in January (table 10).
It was of interest to note that a parallel situation was found in the
fox squirrel (Sciurus g. rufiventer). concurrently trapped in the adja-
cent woodlot. although a mch smaller number of anisals was infected.

as can be seen from table 11, the higher average number of worms
coincided with the peak of percentage of animls infected.

i'here has been considerable research on the host reaction to the cys-

19

ticercus of g. taeniaeformis. Apparently about a month's time is re-
quired for the cyst to reach snail-um sise. In rate it has been shown
that the presence of cysticerci confers an active inunity which pre-
vents the onchospheres from establishing themselves airing any subse-
quent exposure to this parasite (liller and Gardiner. 1931;). his in-
mnity. in fact. may remain as long as 60 days after surdcsl removal
of the cysts (Killer and Nessie. 1932). his innity explains the
small number of cysts usually present. since infective eggs of the ces-
tode are umially not present in great enough concentration to allow for
ingestion of many at one time.
i It is difficult. however. to explain why animals infected with
this parasite were not found during the other months of the year. here
does not appear to be any evidence that the activity of cats varies from
one season to another. According to the imression gained by the present
author (unpublished data) there is no seasonal variation of this parasite
in the Norway rat. and there is no reason to expect any in other rodents.
Gladotaenia sp. maplesis (lprehn. 1932): Bostellum armed with
a double row of small hooks. the testes are arranged in two sharply.
defined lateral fields. which are united behind the ovary In a narrow
bridge. he mority of the testes. however. lie anterior to the ovary.
inner egg-shell thick. but not cross-striated. he cysticerci are found
in the liver of rodents. and the mature cestodes in the intestine of
hawks and. owls.
Only two voles contained qsts identified as cysticerci probably
belonging to this genus. flirty-two hooks were present on the rostel-
lum.

Very little is known about this parasite. dines the concentration

of has!“ and owls in this region seems unusually asst. one would ex-
pect a larger number of cysticerci of this group of cestodes. any two
animals. .5‘. were found infected. one in January and one in lay. he
former contained 3 snll cysticerci. and the latter only 1.

g. obvelata. Diagnosis (Qrehn. 1932): mticle cross-striated.
without vestibule; with two small cervical alas which stop anterior to
the end of the oesophagus. lieuth with three broad lips. each of which
bears a median papilla on the outside. The excretory pore lies some-
what behind the oesophegeal bulb. Hale 1.3 to 1.6 mm long..and 0.115
-_ thidc. he posterior end is wound spirally. the spicale is slightly
curved and 0.085 u long. and 0.007 - thick. Behind this. caudad.
lies the 0.037 - long gubernaculum. he cloaca lies 0.21 s- anterior
to the posterior and. its posterior lip bears a small chitinous hook.
interior to the clones lies an inflation of the mticle. and ahead of
this, three manlons. he met anterior of these lies in about the
middle of the bow. finale 3.5 to 5.7 III long and 0.115 to 0.215 mm
thick. Oesophegns 0.255 to 0.33 an long. besides the 0.085 to 0.1 u
long bulb. he thickness of the oesophagus is about 0.05 to 0.7 II. and
that of the bulb is 0.075 to 0.11 -. rho nerve ring lies 0.1 to 0.13
em posterior to anterior end. he excretory pore is 0J8 - from the
anterior end. he anus lies 0.515 to 0.705 as anterior to the posterior
end. !he vulval lies protruding strongly on a cutiailar elevation 0.51:
to 0.7M mm posterior to the anterior end. !he vagina is 0.17 mm long.
Uterus does not extend posteriorly past the anus. lgg 0.11 to 0.112 8
0.03 to 0.0M» mm; it is embryoaated.

his parasite was co-on thmudwut the year. and the commonest I

parasite found in the voles of this area. 293$ of the animals being

21

infected. It was found that fewer animals were infected during the
first manner. but the average number of worms was higher (table 12
and 13). later. during the winter. a larger proportion of animals
was infected with this parasite. but the average number of worms was
low. his low average number continued on into the second suner as
far as observations were made. Ihle worms were rare. as noted by
other workers (Hall. 1916). but in a few animals a larp proportion
of the worms present were males.
Infection with this parasite is direct. and there does not ap-
pear to be any imity. age or otherwise developed. according to
what has been found in closely related ferns (oilbertson. 19M; !ali-
aferro. 1929). ms 21-25 gram weidzt-group was most heavily parasi-
tired with this nematode (table 1h). where was considerable variation
in average number of worms according to weight-group (table 15).
Protogpirura sp. Diagnosis (fork and Maplestene. 1926): Bob
regularly attemted anteriorly. mouth with two large lateral trilobed
lips each bearing three papillae. each lobe is provided with teeth on
its internal surface; cuticular lateral flanges absent; cervical papil-
lae very anterior. in front of the nerve ring; vestibule cylindrical
and long; oesophagu very long. divided into two parts. thie; poster-
ior extremity spiral; large cylindrical caudal alae present; four pairs
of sligatly pedunculated preanal papillae and. two pairs of large post-
anal papillae. also three or four pairs of small papillae near the tip
of the tail; spicules unequal or subsqual; gibernaculum present. Male;
tail conical and very short; vulva tourds the middle of the body. or
anterior to it; oviJsctor relatively short and simle; uteri divergent.

Oviparous. eggs oval with a thick shell and containing an embryo when

22

deposited. Parasites of manuals.

his nematode was moon-on. and occurred in only 2% of the animals
examined. Nothing can be said of its seasonal occurrence. since so few
animals were infected. According to 3.11 (1916). after leudzart (1567)
and liarchi (1871). the eggs of g. m (helin) are ingested by beetles
of the genus fenebrio. and in five weeks encqmulated infective larvae
are found in the body cavity. be intermediate host of {.micola
Gedoelst is a cockroach (mason-r. 19%).

Nothing is known of the i-unology of this group.

In the nice examined. this nematode did not appear to be patho-
genic. since no gastritis was visible macroscopically. here were no
lesions in the etc-ch comrable with those made by the closely re-
lated Emgtera in other animals. the heaviest infection. with 17
fenale and 3 male worms. all mature. was found in a 63 gram female vole.
his individual appeared to be in normal condition. and contained 9
very nearly full-tern feti. In this animal. the stench contained no
food. and both it and the intestine contained considerable gas. his
was not any post-morten change. since the animal was still alive when
removed from the trap. and was examined about a half-hour afterwards.

he monthly percentage of animals infected with Protogirura can
be seen from table 12. hr the 5 aninls infected with this nentode.
the average number of worms was 7.

Nematomiroides longigiculatus. Diagnosis (Dikmans. 19110): Road
surrounded by a cuticular inflation canon to this group of nematodes.
27 to 30 nicrons wide. without the cuticular inflation. or 35 to 1:0 mi-
crons wide with the cuticular inflation; length of inflation 70 microns.
Oeeophagus 700 to 800 microns long. heretory pore located about 350

33

microns from head end; position of nerve ring not determined. his 5.5
to 6.5 m long by 1% microns wide immediately in front of bursa. Bursa
asymmetrical. with the right lobe considerably larger than the left. Ven-
tral. lateral. and externo-dorsal rays arising separately. the ventro-
lateral ray being the largest; the lateral rays have a canon stem. the
externo-lateral ray being a little shorter than the other laterals and
diverging ventral near the tip; the medic-lateral and postero-lateral
rays are about equal in sise and almost parallel. reaching the margin
of the bursa; the externo-dorsals are long and slender. originating
slightly above the posterior margin of the body and running a more or
less wavy course toward the posterior margin of the bursa. but they do
not. however. reach this margin; no dorsal ray could be found in any of
the four ule specimens available for examination. mioules 3.9 to h
u long.

l'emale from 12 to 13 mm long and about 150 to 160 microns wide in
region of vagina. In the specimens available for examination. the an-
terior part of the bodv was irregularly coiled and twisted and the pos-
terior part was straight except for a Met of about a turn and a half
at the extreme end. A. in other members of the family Belignosomidae.
there is a single ovary and a single uterus. the position of the evi-
Jector could not be made out with certainty. Distance from vulva to
tip of tail 210 to 220 microns; distance from anus to tip of tail about
60 microns. lggs from 80 to 90 microns 1v ho to 1&5 microns.

lhie nematode also was rather uncommon in the voles examined. 2.6%
being infected. Little could be seen as to seasonal occurrence of this
parasite. but there is an increase. both in number of animals infected

(table 12) and in average number of worms in the spring. these nema-

21L

todes were found in the small intestine of the host. and for the 9 ani-
mals infected. the average number of worms was 6. with a maxim of 31
in one vole. lxcept for this latter individual. the highest number pre-
sent wms 5. with 3 being the usual number present.

Bpurlcck (19113) has done some experimental work with the related
species. _B_. m Baylis. which occurs as a normal parasite of wild
house mice. and other rodents. He found that some strains of labora-
tory mice are more susceptible than others. but was unable to draw any
conclusions concerning acquired resistance. l’hen large numbers of lar—
vae were given. the mortality was hidi. me infection apparently lasts
at least 8 mnths.

Spurlock also found that after the eggs of E. 251133 hatch. the
free-living stage is passed in moist fecal material. he larvae are
infective about 6 days after deposition of the feces. and are found on
the surface of the fecal mass. lhe opportunity for the vole to become
infected with this parasite. in view of its feeding habits. is. therefore.
relatively slight.

llton. lord. and Baker (1931) have studied the parasites of some of
the' liropean rodents. and they found 1. m to be a coma parasite
of the wood mouse (god-us szlvaticus). although they did not find it
in either lvutogs or liicrotus. In 692 specimens of ;. szlvaticus. they
found an 85$ infection of adult mice. they also found a hid: incidence
of infection with this nematode during the late winter. and a low inci-
dence during the suner and early when.

according to this work also. the seasonal variation in incidence
of infection with g. m was directly dependent upon the age distri-
bution of the animals. and. therefore. directly correlated with the

25

breeding cycle of the animals.

Erickson (19“) has shown that. in the snowshoe hare. the helminth
parasites are net abundant at the peak of the population cycle of the
here. It was found In nton. hrd. and Baker that there was a higher
percentage of wood mice infected with a. 221.33 at the time of year
Just before the mortality occurred during their study. but no unusual
increase in number.

Ye did not find a sufficientnumber of animals infected with 1.
32213.3 to be able to Ike any observations as to age susceptibility.
Elton. lord. and Baker. however. show definitely that the rate of in-
fection with this nemtode increases with age of the host. in the case
of g. glvaticus.

Dictygcenlus vivipgius. . his nematode. two nles and a female.
was found in the ocean of a single vole. Since it is normally a lung
parasite of ruminants. its occurrence here is purely accidental. here
does not appear to have been any opportunity for error in this record.
since specimens of 2. vivi s had not been handled or were even
present in the laboratory where these examinations were ads. Clean
utensils (Petri dishes) were used for the examination of the crane.
and the living worms were found in the intestinal contents while exam-
ining the same under the low-power binocular microscope. be identi-
fication of these mtodes was confirmed by Dr. G. mum. his can-
not. of course. be considered a normal parasite of the vole.

In so far as could be determined from the limited amount of obser-
vations we were able to make. no phase of the seasonal occurrence “of
the helminths of Incrotus could be correlated with meteorological fac-
tors. Since Inst of the parasites collected during the course of this

26

study have no free-living stage in their life cycle. they are not in
themselves so susceptible to these influences. although their inter-
mediate hosts are no doubt affected. long term studies would be nec-
essary to see the effect of precipitation and telperature on the epi-
demiology of these parasites. Because of the great number of factors
playing a part. such as population cycles. reproductive rhythm. possible
age resistance. as well as meteorological factors. it would be necessary
to carry the studv over a period of one or more complete cycles before
any conclusions could be reached.

Boughton (1937) found a definite correlation between the degree of
parasitism and meteorological and physicgraphical factors in the grouse
in Minnesota. His work. and that of other workers who have recorded
this type of a relationship. had been over a wide area. and it is not
likely that such can be learned concerning this relationship in the
course of a local study only.

It is probable. in the case of the parasites of Micrctus. that the
parasitism runs a parallel course with the population cycle. both reach-
ing the peak at the same time. here is no doubt. conpered with the
examinations of voles made previously. that the degree of parasitism
has been very hid: during the course of this study. It will be of con-
siderable interest to determine whether the decrease in number of ani-
mals will be accompanied by a decrease in the number and kinds of para-

sites present.

27

conclusions

1.

2.

3.

5.

In the course of this study. it has not been possible to correlate
any phase of the epidemiology of the helminths with any meteorologi-
cal or physiographical factor.

In uicnotus. the peak of the degree of parasitism apparently tends
to correspond to the peak of the population cycle.

Jbr the year during which this study was made. the highest incidence
of infection with 2: troeschi occurred during the winter. indicating
an availability of the intermediate host of this cestode during this
season.

ihe intermediate host of 5. nacrcghala apparently is not available
to the voles during the winter months.

In the case of parasites such as Protcspirura. it seems probable
that infection occurs through the accidental ingestion of the in-
termediate host. rathern than any deliberate attempt by the voles

to feed on insects. and this accounts for the relatively low inci-
dence cf infection.

Bo definite age resistance was demonstrable with any of the helminths
studied; in general. the age group containing the largest number of
individuals contained also a greater number of parasitised animals.
in imnity in the vole. as in the rat. probably accounts for the
small number of cysticeri of g. Laeniaefcrmis usually found. any

subsequent infection being prevented.

References cited

Baer. J. G. 1927. Monographie de la Mlle Anoplccephalidae. hppl.
Bulletin Biolog. de fiance et de Belgique.

Bailq. V. 192% Breeding. feeding. and Other Life Habits of liendcw
“1°. (”larch“). Jo mice BGBe 27(8):523‘535e

Baker. J. B... Eamon. B. 1!. 1933. hetero Affecting the Breeding of
the field House (Ilicrotus agestis). Proc. Royal Soc. B.
11331364195.

Beylis. H. A. 19%. Personal Oomnication.
Blair. 1'. 19115. Personal Oo-unication.

Bonditon. 3. 1937. Indoparasitic Infestations in Grouse. heir Path-
ogenicity and correlation with Meteoro-rcpographical Gon-
diticns. 011. of linnescta Ag. Exp. Station Eech. Bull.
121.

handler. A. O. 19%. Introduction to Parasitology. Wiley and Sons.
N. I.

Oulbertson. J. !. 19M. I-unity Against Animal Parasites. Oolumbia
University Press. I. I.

Dice. 1.. R. 1938. Some Oonsus Methods for lie-ale. Jour. Vildl. Nan.
2(3):127.

muthitt. '3. 1915. soon... on the Oestode Pamily anplccqhalidse.
n1. Biol. lionogs. 1( 3).

llton. 0.. lbrd. I. 3.. and Baker. J. B. 1931. he Health and Para-
sites of a Wild louse Pcpulation. Proc. 8ool. Soc. Ion-
don part 3.657-721.

llton. c. 19142. Voles. Mice. and Lemmings. Glarendon Press. Oxford.

hick-son. A. B. 1938. Parasites of Some Minnesota Oricetidae and Za-
podidae. and a Host Oatalogue of Helminth Parasites of
lative American Mice. Amer. Mid. Hat. 20(3):575-589.

Erickson. A. 3. 191m. Helminth Infections in Relation to Population
fluctuations in howshoe Hares. Jour. Iildl. inn. 8(2);
nit-453.

Hall. M. O. 1916. Newsatode Parasites of Mamals of the Orders Rodentia.
Iagomorpha. and Hyracoidea. Proc. U. 8. Natl. the. 50:1-
258.

Hamilton. I. J. 1937. Growth and Life Span of the Pield House. in.
Naturalist 71(736):5oo-w7.

Rarkema. R. 1936. he Parasites of Some North carolina Rodents. Bool-
ogical lbnographs 6(2):l53-232.

Kayne. D. I. 19106. Personal Oomnication.

Irull. V. 1939. Observations on the Distribution and Roology of the
Oribatid Kites. Jour. Nash. Load. Sci. 29(2);518-528.

flichigan Ooneemtion. 1916. 15(2).

Ransoh. R. 19%. Paranaplocghala troeschi sp. nov. from the leadow

Yale (florets: p_. pennszlvanicus). trans. Amer. Iiic. Soc.
in press.

 

Sprehn. S. V. 1932. Lehrbuch der Helminthologie. Borntraeger Verlag.
Berlin.

aux-lock. G. N. 1918. Observations on Host-Parasite Relations Between
Laboratory Mice and Nematcgpiroides dubius Beylis. J. Para-
Incl. 29(5):?3-311-

Stall. N. R. 1935. flapewcrm Studies 11. Persistence of the Pasture
Stage of Honiesia egansa. Amer. J. Hyg. 22:683-703.

Stall. N. R. 1938. Tapeworm Studies VII. Variations in Pasture In-
fections with Naniesia egansa. J. Parasitol. 2h2527.

Stunkard. N. 1937. he 1.1:. cycle of mplacephaline cottons. J.
Parasit. 23:569 (abst.).

Taliaferrc. I. E. 1929.~ he Imnclagy of Parasitic Infections. Gen-
tury 00.. N. Y.

Yorke. V. and Naplestone. P. A. 1926. he Nematode Parasites of Verte-
brates. P. Blakistcn's Son & Oo. Philadelphia.

 

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