Echinococcus multilocularis is a tapeworm species ordinarily considered to be found in wild canids, including foxes, coyotes and wolves. The parasite has also been identified in domestic dogs and cats and potentially is a serious public health concern by involving humans as accidental intermediate hosts.
The life cycle of the parasite is based on a predator-prey relationship, as depicted.
The adult tapeworm is small (1-4 mm) and resides in the intestinal tract of the definitive host (wild or domestic canids). Eggs from the adult tapeworm are shed in the feces of the infected canid. Rodents such as mice and voles serve as the intermediate host for E. multilocularis.
Eggs ingested by rodents develop in the liver, lungs and other organs to form multilocular cysts. The life cycle is completed after a canid consumes a rodent infected with cysts. After ingestion of an infected rodent, larvae contained within the cyst develop into adult tapeworms in the intestinal tract of the canid. Eggs may begin to be passed in the feces of the canid approximately 28 days later.
This parasite poses a serious public health problem because of the possibility for human involvement in the lifecycle. If eggs shed by an infected canid are accidentally ingested, a highly pathogenic condition (Alveolar Hydatid Disease) results from development of the cyst stage in humans.
The original geographic distribution of E. multilocularis was primarily confined to northern areas of North America. Current evidence indicates migration of the parasite well into the continental United States.2,3
Domestic dogs living in E. multilocularis endemic areas that roam freely with the opportunity to catch wild rodents are at risk for infection. Pet owners should be advised on how to minimize this risk. Proper restraint of roaming dogs should be encouraged, along with regular treatment with Praziquantel Tablets, following the established dosage schedule (above) and the precautions indicated below.
Additional information on the life cycle and epidemiology of this parasite is available in veterinary parasitology texts.4,5
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