Montana Field Guide

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Echinococcus multilocularis primarily infects foxes, coyotes, or wolves as a definitive host, and rodents as an intermediate host.

E. multilocularis requires two hosts to complete its life cycle. The adult tapeworm live in the intestine of the definitive host, which is typically a canine. Adult tapeworms lay eggs that are excreted with the feces of the definitive host. In many cases, the definitive host does not suffer adverse effects, even with a relatively heavy parasite burden.

The intermediate host becomes infected by ingesting eggs that were passed with the canine feces. The intermediate host is typically a rodent or occasionally a human. Once ingested, the eggs hatch in the digestive tract of the intermediate host, then enter the blood stream and are carried to organs, primarily the lung, liver, or brain, where they develop into a cyst that contains immature form of the parasite. The number of cysts that develop in an intermediate host ranges from 1 to many. Intermediate hosts with few cysts may not experience significant adverse effects whereas extremely heavy burdens may be fatal.

The parasite life cycle is completed when the intermediate host dies and another carnivore consumes the organs containing parasite cysts. Adult tapeworms again develop in the intestine of the canine definitive host, and begin laying more eggs.