Echinococcus multilocularis, the fox tapeworm, is a small cyclophyllid tapeworm found extensively in the northern hemisphere. E. multilocularis, along with other members of the Echinococcus genus (especially E. granulosus), produce diseases known as echinococcosis. Unlike E. granulosus, E. multilocularis produces many small cysts (also referred to as locules) that spread throughout the internal organs of the infected animal. The resultant disease is called alveolar echinococcosis, and is caused by ingesting the eggs of E. multilocularis.

The parasite is commonly maintained in a wildlife life cycle involving two mammalian hosts. Wild canids, dogs, and less commonly cats act as definitive hosts, harbouring the adult stage of the tape worm. Voles are the intermediate hosts. Ingestion of a rodent containing alveolar hydatid cysts by a wild canid can result in a heavy infestation of tapeworms.

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