Definition of Echinococcus:

Echinococcus is an infection caused by the Echinococcus granulosus or Echinococcus multilocularis worm.

Causes, incidence, and risk factors:

Echinococcus is common in southern South America, the Mediterranean, the Middle East, central Asia, and Africa. In the United States, the disease is very rare, but has been reported in California, Arizona, New Mexico, and Utah.

Humans become infected when they swallow eggs in contaminated food. The infection is carried to the liver, where cysts form. Cysts can also form in the lungs, as well as in the brain, bones, skeletal muscles, kidney, spleen, and other tissues. A liver cyst may produce no symptoms for 10 to 20 years until it is large enough to be felt by physical examination or to produce symptoms.

Risk factors include exposure to cattle, sheep, pigs, or deer or exposure to the feces of dogs, wolves, or coyotes.