The Ecology of Anaplasma phagocytophilum and the Blacklegged tick, Ixodes scapularis in the Upper Midwest, U.S.A.
Ixodes scapularis, commonly known as the blacklegged tick (or deer tick), is a medically important tick species that is spreading multiple diseases in the eastern USA. It is especially important as the vector for transmitting the Lyme disease pathogen, Borrelia burgdorferi and anaplasmosis pathogen, Anaplasma phagocytophilum (Ap). With factors such as habitat restoration, increasing deer densities and climate change, the geographic range of I. scapularis has been expanding. Most of the disease cases are reported from two major foci: the Upper Midwest and the Northeast. With the expansion of I. scapularis it is important to study the ecology of I. scapularis and its associated pathogens. The overall goal in this dissertation was to study the ecology of a tickborne disease and its vector. There are two research chapters and to help understand the context and importance of the research topics, there are two literature review chapters, one to review Ap and one to review Species distribution models (SDMs) with particular attention paid to literature on I. scapularis SDMs.The first research chapter examines the host ecology of A. phagocytophilum at a highly endemic site for I. scapularis in the Upper Midwest. I estimated that eastern chipmunks have relatively greater realized reservoir competence than the white-footed mouse but considering the overall contribution to the enzootic cycle of A. phagocytophilum, white-footed mice may play a larger role because they feed a higher proportion of larvae. Most questing nymphs and all the hosts captured that were infected with A. phagocytophilum were infected with the human pathogenic strain of A. phagocytophilum, Ap-ha. This means that if humans and/or companion canines are bitten by an A. phagocytophilum-infected tick at this field site, there is a high risk that of disease. I found the phenology patterns of infection prevalence of hosts, on-host larvae, and the density of infected nymphs follow that of the phenology patterns of questing nymphs and larvae. Blood and biopsy samples can be used for assaying A. phagocytophilum, but I suggest conducting xenodiagnoses experiments to determine empirically the length of transmission of A. phagocytophilum by each tissue type into larvae. Conclude with what is novel and/or important about the findings. The second research chapter centers on developing species distribution models for I. scapularis in Michigan. In this chapter I looked at the environmental predictors that were important in determining where I. scapularis would occur within Michigan and where suitable habitats for the occurrence of I. scapularis in Michigan are found. I developed models for the Upper and Lower Peninsula. I used two different modeling methods, a logistic regression and a machine learning technique based maximum entropy modeling. For both peninsulas environmental predictors related to temperature, humidity, presence of maple, beech, birch forest types, presence of white-tailed deer, soil moisture, and soil clay content. In the Lower Peninsula, most of the southern regions were considered to have suitable habitat for the occurrence of I. scapularis, while the northern region in the Lower Peninsula had the least suitable habitats for I. scapularis occurrence. In the Upper Peninsula, central southern regions as well as regions along the Lake Superior had suitable habitats for I. scapularis occurrence, while there were pockets of least suitable habitats across the peninsula. Future studies should develop a species distribution model based on the current distribution of I. scapularis in Wisconsin and project it onto Michigan to extrapolate where suitable habitats are found in Michigan. A comparison of that model with the ones we have developed can help us to understand better the invasion process of I. scapularis in Michigan. Furthermore, continuing surveillance efforts in the currently predicted least suitable regions will determine if those habitats really are not suitable for I. scapularis or if it just has not gotten there. Conclude with what is novel and/or important about the findings.Read
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Electronic Theses & Dissertations
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- Attribution-NonCommercial-NoDerivatives 4.0 International
- Material Type
- Thesis Advisors
Tsao, Jean I.
- Program of Study
Comparative Medicine and Integrative Biology - Doctor of Philosophy
- Degree Level
- 220 pages