Anaplasma marginale can be transmitted, will grow and can survive in a large number of domestic and wild animals. It is pathogenic in cattle, and usually produces nonapparent or mild infections in other species. Anaplasma marginale has been recovered from cattle, sheep, goats, water buffalo (Bubalus bubalis), white-tailed deer (Odocoileus virginianus), mule deer (Odocoileus hemionus hemionus), black-tailed deer (Odocoileus hemionus columbianus), pronghorn (Antilocapra americana americana), Rocky Mountain elk (Cervus elaphus nelsoni), bighorn sheep (Ovis canadensis canadensis), black wildebeest (Connochaetes gnu), blesbuck (Damaliscus albifrons), and duiker (Sylvicapra grimmi grimmi). Unidentified anaplasms have been seen in, and in some instances isolated from, Cape buffalo (Syncerus caffer), giraffe (Giraffa camelopardalis), wildebeest (Connochaetes taurinus), Cokes hartebeest (Alcelaphus buselaphus cokii), Thompson's gazelle (Gazella thompsonii), waterbuck (Kobus ellipsiprymnus), and sable antelope (Hippotragus niger), with serological evidence of Anaplasma infection in an even wider range of wild ruminant species. Anaplasma ovis, A. centrale, or other as yet unidentified anaplasms may well occur in other ruminants. With the exception of black-tailed deer, the epidemiologic significance of anaplasmosis in wildlife has yet to be determined. The only wild animal in which Anaplasma is reported to produce serious clinical disease is the giraffe.