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Anaplasma ovis (Rickettsiales: Anaplasmataceae) is a tick-borne pathogen of sheep, goats and wild ruminants. The genetic diversity of A. ovis strains has not been well characterized due to the lack of sequence information. In this study, we evaluated bighorn sheep (Ovis canadensis) and mule deer (Odocoileus hemionus) from Montana for infection with A. ovis by serology and sequence analysis of the msp4 gene. Antibodies to Anaplasma spp. were detected in 37% and 39% of bighorn sheep and mule deer analyzed, respectively. Four new msp4 genotypes were identified. The A. ovismsp4 sequences identified herein were analyzed together with sequences reported previously for the characterization of the genetic diversity of A. ovis strains in comparison with other Anaplasma spp. The results of these studies demonstrated that although A. ovismsp4 genotypes may vary among geographic regions and between sheep and deer hosts, the variation observed was less than the variation observed between A. marginale and A. phagocytophilum strains. The results reported herein further confirm that A. ovis infection occurs in natural wild ruminant populations in Western United States and that bighorn sheep and mule deer may serve as wildlife reservoirs of A. ovis.

Wildlife reservoir species and genetic diversity of Anaplasma ovis (Rickettsiales: Anaplasmataceae) have been poorly characterized. Bighorn sheep (Ovis canadensis), captured in Montana from December 2004 to January 2005, were tested for antibodies to Anaplasma spp.; the presence of A. ovis was determined by the characterization of major surface protein msp4 sequences. Anaplasma antibodies were detected in 25/180 (14%) sampled bighorn sheep and A. ovis msp4 sequences were amplified by polymerase chain reaction (PCR) and sequenced from 9/23 (39%) of seropositive animals. All animals were negative by PCR for the related pathogens, Anaplasma phagocytophilum and Anaplasma marginale. All msp4 sequences identified in the bighorn sheep were identical and corresponded to a single A. ovis genotype that was identical to a sheep isolate reported previously from Idaho. The finding of a single genotype of A. ovis in this wild herd of bighorn sheep was in contrast to the genetic diversity reported for A. marginale in cattle herds in the western United States and worldwide. These results demonstrated that bighorn sheep may be a wildlife reservoir of A. ovis in Montana.