Echinococcus multilocularis (tapeworm)

Foxes and coyotes, wolves and other wild canids are the definitive hosts while rodents are the normal intermediate host. With the increasing encroachment of humans and domestic pets on wildlife there is an increased risk of cats and dogs being definitive hosts and passing the eggs on to humans.

	E. multilocularis is most common in the northern hemisphere including the northern United States, but the parasite is moving south with dogs and cats as definitive hosts. Humans are an aberrant intermediate host. Disease in humans can be very aggressive and damaging.
	life cycle

Dogs

E. multilocularis does not cause significant disease in the dog.

Diagnosis is difficult because adult worms are very small (1-6 mm) and eggs cannot be differentiated from the common Taenia tapeworm of dogs. So dogs that live in the northern United States should be treated prophylactically whenever any Taenia-like eggs are found on fecal examination.

Treatment: Administration of praziquantel is recommended.

Humans

Infection with E. multilocularis leads to the development of alveolar hydatids. These are much more aggressive than hydatid cysts of other Echinococcus species. The organism reproduces asexually by budding and extension into surrounding tissue rather than into the cyst itself. Most alveolar hydatids are found in the abdominal cavity of infected humans usually in the liver. Here E. multilocularis behaves as a slow growing destructive mass with abdominal pain, biliary obstruction, and occasional metastatic alveolar hydatids are sent to the lung and brain.

cerebral hydatidosis

Diagnosis: The diagnosis of echinococcosis is done with ultrasound and positive serologic tests. Ultrasound guided fine needle biopsy can be used to confirm diagnosis. Caution is imperative as rupture of the cyst will seed the abdominal cavity with daughter cysts.

Treatment: Surgery is the most common form of treatment. After surgery, medication must be taken to keep the alveolar hydatid from growing again. Albendazole has been used successfully to treat E. multilocularis.

Prevention: . People are infected by ingesting the eggs of Echinococcus that have been passed in the feces of cats or dogs. The fecal exposure can come from petting dogs that have rolled in fox feces and then putting your hands near your mouth. Exposure can also occur during necropsies by veterinarians, when opening the bowels in wild canids or dogs in the northern hemisphere.

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