Abstract

In the last decade, two human ehrlichiosis agents have emerged as public health concerns in the United States: Ehrlichia chaffeensis, which causes human monocytic ehrlichiosis (HME), and an organism closely related or identical to Ehrlichia equi which causes human granulocytic ehrlichiosis (HGE). Both organisms apparently are transmitted among wildlife reservoirs and to humans by ticks. Serologic, PCR-based, and culture-based surveys of white-tailed deer populations have revealed that deer in the southeastern United States commonly harbor E. chaffeensis. Results of PCR tests also show wild deer are infected with the HGE agent and another novel Ehrlichia-like organism which to date has not been reported as a cause of human disease. The presence of multiple Ehrlichia spp. in wildlife reservoirs or tick vectors can present challenges to developing reliable diagnostic tests for epidemiologic surveys. However, in areas where purported tick vectors of both E. chaffeensis and the HGE agent coexist, deer populations may be coinfected with multiple Ehrlichia spp. In a survey of a deer population in coastal Georgia, serology and PCR indicated multiple individual animals had each been exposed to at least three Ehrlichia spp. Such data underscore the importance of white-tailed deer in the natural history of human ehrlichiosis and indicate deer could serve as a valuable sentinel species for studies on the geographic distribution of human ehrlichiosis agents in the United States.