Dissertation/Thesis Abstract

Eco-epidemiology of Borrelia burgdorferi in the northeastern United States: effects on transmission due to tick distributions among vertebrate hosts
by Tsao, Kimberly, Ph.D., Yale University, 2012, 63; 3525286
Abstract (Summary)

Borrelia burgdorferi, the bacterial agent of Lyme disease, is inextricably linked to the ecology of its vertebrate hosts and tick vectors. In eastern North America, the bacterium is entirely dependent on the black-legged tick, Ixodes scapularis, to spread and infect new hosts. Of the many ecological factors involved in this system, I focus on one that plays an important role in issues ranging from wildlife vaccination to bacterial evolution. An I. scapularis tick takes its first blood meal from one of a number of vertebrate host species and acquires B. burgdorferi, an epidemiologically significant event because this is the main route by which B. burgdorferi finds its next host. How the tick population is divided among different host species for these first meals can have substantial impacts on B. burgdorferi transmission and evolution.

I have primarily taken a simulation modeling approach to explore how tick distributions among different host species: a) affect the impact of a wildlife-targeted vaccine intended to reduce human Lyme disease risk, and b) affect selective pressure on the bacterium, mediated by host immune responses and host life history. Field data were collected to support model assumptions. In order to analyze these data, I modified the terminal restriction fragment length polymorphisms (T-RFLP) method to efficiently identify genetic types of B. burgdorferi from field samples, which improves on current techniques in both cost and efficiency.

Because I. scapularis feed on a wide variety of mammalian and avian hosts, there are a wide variety of transmission outcomes depending on how the ticks distribute themselves among those hosts. One host responsible for feeding a large proportion of larval ticks is the white-footed mouse ( Peromyscus leucopus). If larval distributions are disproportionately weighted towards this species, as they likely are, there are multiple consequences for B. burgdorferi transmission. Wildlife vaccination will not eliminate B. burgdorferi from local areas, in part because of the contribution of other hosts, however small, to maintaining this pathogen in nature. Also, because of the one-year lifespan of P. leucopus, vaccination programs targeting these mice would need to be repeated on an annual basis. This short lifespan also affects the evolution of the bacterium: P. leucopus does not live long enough for acquired immunity in the population to provide selective pressure on B. burgdorferi.

The two issues addressed here are both are strongly influenced by tick distributions among host species. Improving our ability to measure these tick-host associations in nature will certainly benefit our understanding of the ecology and epidemiology of this system.

Indexing (document details)
Advisor: Fish, Durland
School: Yale University
School Location: United States -- Connecticut
Source: DAI-B 73/12(E), Dissertation Abstracts International
Subjects: Ecology, Evolution and Development, Epidemiology
Keywords: Borrelia burgdorferi, Lyme disease, Tick distributions, Wildlife vaccination
Publication Number: 3525286
ISBN: 9781267574039
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