Classification: ICD-9 122.7; ICD-10 B67.5–B67.7
Syndromes and synonyms: Alveolar or multilocular echinococcosis.
Agent: Echinococcus multilocularis, a small (3–6 mm long) cyclophyllid cestode (tapeworm).
Reservoir: Foxes (including urban foxes) are the definitive hosts, wild rodents (mainly Arvicolidae), voles and lemmings are intermediate hosts. Foxes have extended their distribution into urban areas, partly due to a decrease in rabies deaths in foxes since rabies vaccination.
Transmission: Ingestion of tapeworm eggs from feces of foxes, dogs, and cats or contaminated fomites. There is no person-to-person transmission.
Cycle: Fox–rodent–fox (sylvatic cycle). Foxes are the definitive hosts of the adult worm. Eggs are excreted with the feces and ingested by humans or the intermediate rodent host, where they hatch. The larvae penetrate the intestinal wall and via the blood they reach the liver, lungs, brain, and heart. There they form metacestodes in which protoscolices develop. When the rodent is eaten by the definitive host, these attach to the small intestine and grow into adult worms. Occasionally wild carnivores (e.g. coyotes or wolves) can be definitive hosts. In some rural areas there is a synanthropic cycle in which dogs or cats are definitive hosts, acquiring the parasite from wild rodents.
Incubation period
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