Evaluation of free-roaming mule deer as carriers of anaplasmosis in an area of Idaho where bovine anaplasmosis is enzootic.

Samples of blood from 87 Rocky Mountain mule deer (Odocoileus hemionus hemionus) were inoculated into 3 susceptible splenectomized calves to determine the anaplasmosis carrier status of the deer. The deer were trapped along the Idaho-Utah state boundary, near Stone, Id. Acute anaplasmosis was induced in 2 of the 3 inoculated calves, and blood from the 3 calves caused anaplasmosis when inoculated into adult non-splenectomized cattle. Serum rapid card agglutination testing revealed 13 (14.9%) positive reactions among the 87 mule deer. When these seropositive samples were evaluated with the complement-fixation test, positive reactions were not found and only 3 (3.5%) serums gave suspect reactions. A serologic survey for anaplasmosis in 1,852 cattle that cohabit spring and summer rangeland areas with mule deer revealed 14.5% reactors by the serum rapid card agglutination test. The study area consisted of an ecosystem that supports cattle, free-roaming mule deer, and Dermacentor andersoni, and thus contained the elements necessary to effect interspecies transmission of Anaplasma marginale. The significance of wildlife reservoirs and their bearing on anaplasmosis control and eradication programs needs further investigation.