Prevalence and Intensity of Besnoitia sp. Infection in Migratory Caribou (Rangifer tarandus) Herds in North America

Besnoitia tarandi is a protozoan commonly reported in reindeer and caribou (Rangifer tarandus spp.), in which it can be associated with morbidity and even mortality. Anecdotal observations suggest that the prevalence and intensity of this parasitic infection vary between caribou herds, but the lack of a standardized method to evaluate the intensity of infection limits inter-herd comparisons. The presence and intensity of Besnoitia sp. infection in metatarsal skin were evaluated using a standardized histopathologic technique in 1,361 migratory caribou sampled from eight herds across Canada, Alaska (USA), and Greenland. Besnoitia sp. was not detected in the two Greenlandic herds but was observed in animals from the six other herds sampled, with prevalence ranging from 4.2-63.9% for subsets of caribou by season and/or sex, and cyst density ranging from 0.08-13.14 cysts/mm2 among herds. Observed prevalence of infection was highest in the two Canadian Québec-Labrador herds (Rivière-George and Rivière-aux-Feuilles) and lowest in the Canadian Southampton Island herd. This study provides new insights into the epidemiology of besnoitiosis in migratory caribou populations in North America.