Hydatid Tapeworms

Causative agent: Taenia hydatigina, Echinococcus granulosis
T. hydatigenia is found in North America, E. granulosis is found world wide (56). The adult forms of these two tapeworms live in the intestinal tracts of their primary hosts, wild and domestic carnivores. They release eggs that are carried out of the host in the feces. If the eggs are consumed by a secondary host, including cattle, sheep, bison and other herbivores, the eggs will hatch in the intestinal tract and migrate to the liver, lungs and peritoneal cavity. Once they reach these locations the parasites will form cysts, called cysticerci or hydatids. If a carnivore that is consuming the infected carcass of a secondary host, eats a hydatid cyst or cysticrecus, the life cycle will be completed, with the adult stage of the parasite developing in the intestinal tract.
Disease will occur when secondary hosts are kept in close contact with primary hosts, such as dogs, or when primary hosts contaminate the secondary hosts (bison) food source. When the secondary host (bison) consumes large quantities of eggs, multiple cysts may be formed in the liver or lungs. These cysts can cause severe damage to these organs, resulting in organ failure and disease.

Clinical signs:
T. hydatigina has been found in bison, but was not associated with disease (50). E.granulosis has been found in American bison in a zoo in India, however the clinical signs, if any, were not reported (55).

Postmortem findings:
Pathological changes associated with E. granulosis infection in bison include hepatomegaly, hydatid cysts in the liver, and hydatid cysts in the lungs (55).

There are no specific tests that can be used to diagnosis the presence of hydatid cysts in the secondary host.

There have been no treatments reported for hydatid cysts in bison. In man, hydatid cysts are treated with mebendazole, albendazole, praziquantel, or surgical removal (56). It is not known how effective these treatments would be for bison.

Since the source of infection is eggs in carnivore feces, control should be achieved by preventing the contamination of bison feed and pasture with carnivore feces. This will be impractical when bison are on pasture. During winter-feeding, the most likely source of infection will be farm dogs. If farm dogs are suspected to be the source of E.granulosis they should not be allowed access to bison feed or feeding areas. To prevent farm dogs from becoming infected they should not be allowed to eat the carcasses of bison, cattle or other herbivores, such as deer or moose. They should not be fed scraps or raw meat taken from carcasses of herbivores that have been hunted for food. Farm dogs should be tested periodically for the presence of tapeworm eggs in their feces and treated if eggs are present.


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