Population Genetic Structure of Ixodes scapularis and disease transmission
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abstract
The long-term goal of this research project is to improve our understanding of Lyme disease (LD) transmission through the study of the population genetics of the arthropod vector in the Southern US. This integrated ecological approach will provide significant information on the competence of I. scapularis as a B. burgdorferi vector when feeding from different vertebrate host-species. By capitalizing on the ecological variation among geo-climatically distinct regions in Texas, this study will provide bothan ecological and genetic framework to characterize the transmission of LD to humans in the South-Central United States. LD is the most prevalent arthropod-borne disease in the US with 33,097 cases reported to the CDC during 2011. Almost all LD studies completed to date are focused in the Northeast and Midwest regions of the US where this disease is more prevalent, with no major studies done in Southern US. There is a critical need to determine the ecological factors promoting the differential incidence of LD even though the agent, vector and mammalian hosts are present in both geographic regions. In addition, there is limited information on the genetic diversity of I. scapularis and on the role this genetic diversity has in explaining the ris of contracting LD. We will use recent insights into the host use ecology and genetics of other tick species as a baseline to explore if the same phenomenon occurs in I. scapularis. Host availability, diversity and abundance vary across both spatial and temporal scales. Therefore, individuals of a given vector species may be subjected to distinct selective pressures in differentgeographic portions of its distribution. This may result in vector populations being structured by geography, host species or a combination of both. At its most basic level, understanding patterns of spatial variation in host use by polyphagous vectors of animal diseases, requires the collection of host use data at both fine and course resolutions. Consequently, we will approach this issue by proposing two specific aims. Specific Aim 1: Quantify local host use patterns and B. burgdorferi infection in Ixodes scapularis in two contrasting environments in Texas (Pinewoods and Post Oak Savannah) within the geographic distribution of I. scapularis. We will also test for differences of vertebrate host communities, tick prevalence and B. burgdorferi infection between anthropogenically degraded and sylvan habitats at the selected Texas eco- regions. (Dr. Esteve-Gassent, Dr. Castro-Arellano). Specific Aim 2: We will test for genetic population structure and host associated genetic differentiation of I. scapularis across the different eco-regions outlined above (Dr. Medina). At the completion of these studies, it is our expectation that we will have identified the local host use patterns of I. scapularis, as well as te host associated genetic differences. We also expect to have delineated the distribution of B. burgdorferi in the studied vertebrate hosts and evaluated their competence as reservoirs for this pathogen in the state of Texas.
