Anaplasma marginale

Anaplasma marginale is a rickettsial organism that infects the erythrocytes of cattle and is transmitted by ticks.  The organism occurs around the world, but rarely in Canada, where it is a federally reportable disease.  To date (June, 2011), anaplasmosis in cattle in this country has been reported only in Quebec, Ontario, Manitoba and Saskatchewan.  Symptoms of clinical anaplasmosis in cattle include anaemia, fever and jaundice, but not all infected cattle are symptomatic.  The primary vectors for A. marginale in Canada are the ixodid ticks Dermacentor andersoni and D. variabilis.  An interesting recent investigation of suspected anaplasmosis in cattle in British Columbia, where seroprevalence is significantly higher than in other provinces, demonstrated that the organism detected was not A. marginale, but an apparently new species or genotype of Ehrlichia.  Only one species of Ehrlichia has been reported previously from cattle - E. ruminantium, the cause of heartwater in cattle, sheep and goats in sub-Saharan Africa and areas of the Caribbean.  The origin and epidemiology of the Ehrlichia in cattle in British Columbia have not yet been fully explored, and it is possible that the infected cattle had acquired the pathogen from white-tailed deer, in which an Ehrlichia sp. closely related to E. ruminantium are known to occur in the US. A recent PCR-based survey of mule deer and white-tailed deer in the same area of British Columbia suggests the possibility of transmission of this Ehrlichia species through tick vectors between cattle and free-ranging cervids.

Howden KJ et al. (2010) An update on bovine anaplasmosis (Anaplasma marginale) in Canada.  Canadian Veterinary Journal 51: 837-840.

Gajadhar AA et al. (2010) A novel Ehrlichia genotype detected in naturally infected cattle in North America. Veterinary Parasitology 173: 324-329.