The apicomplexan protozoan Besnoitia infects cattle and goats in tropical and subtropical countries, especially in Africa. It has not been reported in cattle in Canada but B. tarandi has been reported frequently in free-ranging caribou and reindeer, and a recent serosurvey found evidence of the Besnoitia spp. infection also in muskoxen and bison, but not in elk, white-tailed deer or moose. The species in these hosts is B. tarandi, but the taxonomy within the genus has not yet been fully determined. Tissue cysts of Besnoitia spp. are found in connective tissue, measure 0.18-0.22 mm by 0.28-0.32 mm and contain bradyzoites surrounded by a thick connective tissue capsule.

Besnoitia has an indirect life cycle with the cattle, goats, caribou, mule deer and reindeer as intermediate hosts and in some species a feline definitive host, although the definitive host has not yet been identified for all species of Besnoitia. Transmission is thought to be through the intermediate host ingesting the sporulated oocysts in the faeces of definitive hosts. Mechanical transmission by insects might also be possible since during an epidemic at the Assiniboine Park Zoo in Winnipeg, Manitoba, the infection was transmitted between caribou, mule deer and reindeer that were housed in separated pens and had no access to carnivore faeces. In the intermediate host the sporozoites excyst and reproduce asexually becoming tachyzoites which form cysts in the connective tissue in the skin, conjunctiva, mesentery and scrotum of the intermediate host. The cysts contain bradyzoites and are predominently found in fibroblasts. The life cycle continues when the tissue containing the cysts is ingested by a definitive host following which the bradyzoites undergo merogony and gametogony in enterocytes of the small intestines and unsporulated oocysts are passed in the faeces. Oocysts sporulate in the environment.

Guiterrez-Exposito D et al. (2012) Serological evidence of Besnoitia spp. infection in Canadian wild ruminants and strong cross-reaction between Besnoitia besnoiti and Besnoitia tarandi. Veterinary Parasitology 190: 19-28.

Leighton FA, Gajadhar AA (2001) Besnoitia spp. and besnoitiosis. Parasitic Diseases of Wild Mammals 2: 468-478.

Glover G et al. (1990) An epizootic of besnoitiosis in captive caribou (Rangifer tarandus caribou), reindeer (Rangifer tarandus tarandus) and mule deer (Odocoileus hemionus hemionus). Journal of Wildlife Diseases 26: 186–195.