Population genetics and pathogen surveillance of ticks collected from Arkansas canines and white-tailed deer.

摘要

Ticks (Acari: Ixodidae) have been implicated in the transmission of several protozoan, viral, and bacterial agents. The objective of my dissertation was to identify the ticks infesting Arkansas domestic canines (Canis lupus familiaris L.) and white-tailed deer (Odocoileus virginianus Zimmerman), determine the structure of the most common ticks infesting each host, and determine the prevalence and distribution of Borrelia and Rickettsia in the tick and host population.;Five tick species were collected: Ixodes scapularis Say (51%), Amblyomma americanum (L.) (22%), Rhipicephalus sanguineus (Latreille) (12%), A. maculatum (Koch) (7%), Dermacentor variabilis (Say) (6%), and 2% were composed of unidentified Amblyomma species. A majority of the collections were adults (84%). Canine collections were primarily A. americanum (45%), whereas I. scapularis was the most common tick infesting deer (89%).;The two most-common ticks, A. americanum and I. scapularis, were found infesting the same hosts. Therefore, their population genetics were studied to provide insight into their dispersal patterns and population structure, and to identify locations with a chance for high selection pressure. Thirty-three haplotypes of A. americanum were identified, of which 23 haplotypes occurred once. Eighteen I. scapularis haplotypes were identified, of which 11 haplotypes occurred once. The excess of low-frequency haplotypes in both A. americanum and I. scapularis populations indicated that their populations are expanding in the Arkansas ecosystem. The increased haplotype diversity and nucleotide diversity found in this study suggested that both species have increased gene flow and are randomly mating across the state because of each tick's use of multiple hosts in various habitats.;Due to the high incidence reports of bacterial pathogen transmission, I screened subsets of the previously described collections for Rickettsia and Borrelia pathogens. The cause of spotted fever cases in the southern United States is a subject of debate; consequently, I screened Amblyomma maculatum ticks for Rickettsia -genus specific genes gltA and rompB. Sixty-two of the 207 ticks were PCR-positive (30%). Sequencing results were homologous with R. parkeri, Candidatus R. amblyommii, and an uncharacterized Rickettsia sp. sequence (EF219464). Due to the uncertainty of Borrelia transmission in the southern U.S., I screened a subset of the collected ticks and their host's blood for Borrelia pathogens by amplifying the flaB region for Borrelia (a genus-specific gene). Of all the ticks tested (n = 2121), 28% were positive with flaB for Borrelia. Genetic sequencing identified B. lonestari (suggested causative agent for Southern Tick Associated Rash Illness) as the primary Borrelia in these Arkansas ticks, but B. burgdorferi (causative agent for Lyme disease) was also identified.;With the findings of several tick species infesting different hosts, a high probability of gene flow, expanding tick populations, and the incidence of several Borrelia and Rickettsia, it is essential to conduct additional research on tick-bacteria interactions. The risk for tick-borne diseases in Arkansas and potentially in the southeastern United States may be greater than previously expected. Additional research should be focused on active surveillance on the ticks and the pathogens, determination of each bacterium's pathogenesis within each tick species, and their relationship to human disease. Genetic variation of each bacteria and each tick along with variation of symptoms should be considered and compared to known cases of tick-borne diseases in the northeastern and western United States to obtain accurate prevalence and incidence rates and to identify localized hot spots for pathogen surveillance and tick management. (Abstract shortened by UMI.)