Echinococcus Multilocularis - Life Cycle

Life Cycle

The life cycle of E. multilocularis involves a primary or definitive host and a secondary or intermediate host, each harboring different life stages of the parasite.

Foxes, domestic dogs and other canids are the definitive hosts for the adult stage of the parasite. The head of the tapeworm attaches to the intestinal mucosa by hooks and suckers. It then produces hundreds of microscopic eggs, which are dispersed through the feces (Vuitton, 2009).

Wild rodents such as mice serve as the intermediate host. Eggs ingested by rodents develop in the liver, lungs and other organs to form multilocular cysts. Humans could also become an intermediate host by handling infected animals or ingesting contaminated food, vegetable, and water. The life cycle is completed after a fox or canine consumes a rodent infected with cysts. Larvae within the cyst develop into adult tapeworms in the intestinal tract of the definitive host (Vuitton, 2009).

Except in rare cases where infected humans are eaten by canines, humans are a dead-end or incidental host (an intermediate host that does not allow transmission to the definitive host) for E. multilocularis.

Summary of the life cycle

1. adult worm present in intestine of definitive host
2. eggs passed in feces, ingested by humans or intermediate host
3. onchosphere penetrates intestinal wall, carried via blood vessels to lodge in organs
4. hydatid cysts develop in liver, lungs, brain, heart
5. protoscolices (hydatid sand) ingested by definitive host
6. ingested protoscolices attach to small intestine and develops into adult worm