First Report Of A Tapeworm, Taenia Arctos In North American Bears

450px-Medved_mzooTapeworms of the Genus Taenia (Class: Cestoda) are endoparasites that reside in the gastrointestinal tract of a final host from where they shed hundreds and thousands of eggs in the feces. Environment that is contaminated with eggs is the source of infection for the intermediate host in which the larval stages develop. The site of larval development in the intermediate host varies (muscle/brain/abdominal cavity, etc.) depending on the species of Taenia. To complete their life-cycle, larval stages in the intermediate host must be eaten by the final host. In general, Taenia infection is well tolerated by the final host. However, in the intermediate host, clinical signs depend on the organ infected.

In North America, the larval stages of Taenia in the muscle of cervids (caribou and moose) were considered as that of Taenia krabbei, a parasite whose final hosts are wolves, bear and lynx. With the recent discovery of T. in Fennoscandia [Final host: Finnish brown bears; Intermediate host: Finnish Eurasian elk (Alces alces)], there is a strong indication of ‘hidden’ diversity of Taenia spp. that use wild carnivore-wild ungulate system for their life-cycle. More recently, molecular studies confirmed the occurrence of larval forms of T. arctos in Alaskan moose (Alces americanus). However, the final hosts for T. arctos in North America are not known.

As a part of MSc thesis on helminths of bears in western Canada, Stefano Catalano (Supervised by Padraig Duignan and Mani Lejeune of the CWHC Alberta node) collected Taenia specimens from the intestine of a grizzly and a black bear from Alberta and were able to confirm their identity as T. arctos through genetic analysis. This is the first report of the final hosts for T. arctos in North America ( Since the time this article was published, T. arctos from three more black bears (two from Alberta, one from British Columbia) were collected and confirmed. These findings indicate geographic range of T. arctos greater than that was known previously and also suggest potential misidentification of Taenia spp. in bears and moose.

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