An assessment of the role of white-tailed deer in the epizootiology of anaplasmosis in the southeastern United States

The role of Odocoileus virginianus in the epizootiology of anaplasmosis in the southeastern USA was examined through retrospective and prospective serosurveys and by experimental infection studies. No serum antibody reactive to Anaplasma marginale was detected with an indirect fluorescent antibody (IFA) assay from any of 1376 free-ranging deer sampled from 1968 through 1990 from 13 states and Puerto Rico. 31 additional deer from 3 bovine anaplasmosis enzootic premises also were negative by IFA and Giemsa-stained blood films. 3 captive deer given A. marginale intravenously developed antibodies 38-41 days post-inoculation (DPI) and remained seropositive for the duration of the study (161-287 DPI). At 42 DPI, rickettsaemias of _0.0001% infected erythrocytes were observed in all 3 deer using DNA probe; low rickettsaemias (maximum 0.01%) persisted through 56, 63 and 87 DPI, respectively. 1 deer had a recrudescent infection from 126-146 DPI (maximum rickettsaemia 0.001%). It is believed that white-tailed deer in the southeastern USA, even though susceptible to A. marginale infection, are not exposed naturally, even at enzootic sites. Furthermore, white-tailed deer did not develop rickettsaemias sufficient to support mechanical transmission by biting flies (especially Tabanidae), which is believed to be the primary means of anaplasmosis transmission in this region.