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.
|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|
Copyright in each Dissertation and Thesis is retained by the author. All Rights Reserved
The supplemental file or files you are about to download were provided to ProQuest by the author as part of a
dissertation or thesis. The supplemental files are provided "AS IS" without warranty. ProQuest is not responsible for the
content, format or impact on the supplemental file(s) on our system. in some cases, the file type may be unknown or
may be a .exe file. We recommend caution as you open such files.
Copyright of the original materials contained in the supplemental file is retained by the author and your access to the
supplemental files is subject to the ProQuest Terms and Conditions of use.
Depending on the size of the file(s) you are downloading, the system may take some time to download them. Please be