SUSCEPTIBILITY OF WHITE-TAILED DEER (ODOCOILEUS-VIRGINIANUS) TO INFECTION WITH EHRLICHIA-CHAFFEENSIS, THE ETIOLOGIC AGENT OF HUMAN EHRLICHIOSIS

Although more than 320 cases of human ehrlichiosis have been diagnosed in 27 states since 1986, the reservoir host or hosts remain unknown. Since antibodies reactive to Ehrlichia chaffeensis, the etiologic agen t of human ehrlichiosis, have been found in white-tailed deer (Odocoil eus virginianus), we experimentally evaluated the susceptibilities of four white-tailed deer to infection with E. chaffeensis and Ehrlichia canis, a closely related species. A fifth deer served as a negative co ntrol. Isolation and nested PCR amplification results from peripheral blood indicated that E. chaffeensis circulated for at least 2 weeks. T he deer developed antibodies to E. chaffeensis by day 10 after inocula tion, but there was no indication of clinical disease. Immunohistochem ical staining identified E. chaffeensis within macrophage-type cells i n lymph nodes. The deer inoculated with E. canis did not become infect ed and did not seroconvert. These results indicate that white-tailed d eer can support an E. chaffeensis infection with resulting rickettsemi a of at least 2 weeks. The resistance to infection and the absence of seroconversion upon exposure to E. canis indicate that antibody respon ses previously detected among wild deer are not E. canis cross-reactio ns. The role of deer as competent reservoirs in the life cycle of E. c haffeensis remains to be explored with suspected tick vectors.