Echinococcosis

(cystic echinococcosis, alveolar echinococcosis)

Echinococcosis in humans is caused by infection with the larval stage of tapeworms in the genus Echinococcus.  Domestic dogs, wild canids (foxes, coyotes, and wolves), and in some instances cats, serve as the definitive hosts for these tapeworms, harboring the adult tapeworms in their small intestines.  Eggs from the adult tapeworms are shed in the feces of the definitive hosts and subsequently contaminate soil, water, and plants.  Eggs may remain viable in the environment for up to 1 year.  Intermediate hosts, including sheep, cattle, goats, pigs, small rodents, and humans, become infected by ingesting the tapeworm eggs.  Eggs hatch into larvae within the intestine of the intermediate host and migrate throughout the body, where they can form cysts or tumors in a variety of organs.  The tapeworm lifecycle is completed when a definitive host eats the tissues of an infected intermediate host.  Transmission to humans most often occurs through the ingestion of Echinococcus eggs in water or food contaminated with dog or cat feces or by direct hand-to-mouth inoculation after handling contaminated soil or infected dogs and cats and not practicing adequate handwashing.

In humans, larval cysts and tumors may form in a variety of organs, most commonly the liver and lungs.  Infections may remain asymptomatic for long periods, until cysts or tumors grow large enough to disrupt normal organ function.  Clinical signs and symptoms are dependent on the affected organs and the extent of infection.  Organ failure and even death can occur in severe disease.

Prevention measures for human infection include avoiding contact with wild canids; preventing contact between domestic dogs and cats and wild animals; preventing domestic dogs and cats from ingesting tissues from wild animals and livestock; avoiding food or water that may be contaminated with feces from definitive hosts; and practicing thorough handwashing immediately after handling dogs, wild canids, and cats or working in soil.

For more information on echinococcosis provided by the U.S. Centers for Disease Control and Prevention, see http://www.cdc.gov/parasites/echinococcosis/. 

For more information on echinococcosis provided by the World Health Organization, see http://www.who.int/mediacentre/factsheets/fs377/en/.