TAENIA PISIFORMIS

The adult stage of T. pisiformis has been described from the small intestine of coyotes, wolves, coyote-dog hybrids, gray fox, red fox, lynx and bobcat in North America.  In Ontario T. pisiformis was found in 66 of 68 coyotes but in only 7 of 58 timber wolves collected between 1957 and 1960 (Freeman et al., 1961).

T. pisiformis eggs are eliminated from the carnivore host with faeces.  Various species of hares and rabbits are the main intermediate hosts and become infected by eating vegetation contaminated with eggs.  The intermediate stage, the cysticercus, has also been reported from beaver, muskrat and squirrels.  In Ontario the cottontail is the most common intermediate host.

The cysticercus stage was once known as Cysticercus pisiformis but was later recognized as the intermediate stage of T. pisiformis.  The cysticerci are bladder-like cysts about the size and shape of a pea and are usually located in the abdominal cavity amongst vital organs.  There may be anywhere from just a few cysts to well over 100 cysts in an intermediate host.  There is usually little obvious pathology associated with cysticerci and they are not considered to be a mortality factor in cottontails.

   The viscera of infected cottontails and hares should be destroyed either by deep burial or by burning in order to disrupt the life cycle of the parasite.  On no account should infected viscera be fed to dogs.

T. pisiformis is not transmissible to man.  The meat of rabbits and hares is safe for human consumption following the removal of the infected viscera.

Selected References:

Freeman, R.S., A. Adorjan and D.H. Pimlott. 1961.  Cestodes of wolves, coyotes, and coyote-dog hybrids in Ontario.  Can.  J. Zool. 39:527-532.

Thornton, H. 1962.  Textbook of meat inspection, including the inspection of rabbits and poultry, 4th ed. Baillière, Tindall and Cox, London.\