White-tailed deer and raccoons as hosts for selected zoonotic tick-borne rickettsiae
DUGAN, VIVIEN GRACE
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The central aim of this research was to develop a more complete epidemiologic understanding of Anaplasma phagocytophilum, Ehrlichia chaffeensis, Ehrlichia canis, and Ehrlichia ewingii in the southeastern United States. These bacterial cause clinical infection in humans, dogs and/or horses, are transmitted by three different genera of ticks, and involve wildlife in their epidemiology. Raccoons (Procyon lotor) and opossums (Didelphis virginianus) from Georgia were examined for their role in the maintenance of these ehrlichial and anaplasmal species. Raccoons were positive for antibodies to E. chaffeensis, E. canis, and to a lesser extent, A. phagocytophilum and blood from one raccoon was PCR positive for E. canis. All raccoons were PCR negative for E. chaffeensis, E. ewingii, and A. phagocytophilum; however, a novel Ehrlichia-like gene fragment was amplified from over half of the raccoons. In contrast, opossums were negative by all assays. These findings suggest that raccoons, but not opossums, may be involved in the epidemiology of one or more of these pathogens. White-tailed deer (WTD; Odocoileus virginianus) were evaluated for their suitability as natural sentinels for discerning the geographic distribution of A. phagocytophilum across 19 states. This goal was accomplished by testing 2,666 WTD from 507 populations for A. phagocytophilum-reactive antibodies, with confirmatory PCR testing and in vivo xenodiagnostic cultures. WTD met crucial standards as sentinels and evaluation of field data indicated that WTD antibodies reflect infection, small sample sizes were adequate for accurate surveillance, and A. phagocytophilum infection in WTD was correlated with the presence of I. scapularis. Serologic WTD data were used in two different modeling analyses to predict the distribution of A. phagocytophilum across 19 states. Kriging and logistic regression model analyses disclosed moderately high (> 64%) accuracy, sensitivity, and specificity and the projected distribution conformed to human case data available for this region. Additionally, analyses determined significant ecologic variables associated with the presence of A. phagocytophilum. This study demonstrated that WTD would be an effective surveillance species and represent a feasible alternative to human surveillance in predicting the geographic distribution of locations where there is a risk of A. phagocytophilum infection.