infectious diseases
Echinococcosis
Pathophysiology of Echinococcosis
Ingested eggs from animal feces (which may be present on the fur of dogs or other animals) hatch in the gut and release oncospheres (immature forms of the parasite enclosed in an embryonic envelope). Oncospheres penetrate the intestinal wall, migrate via the circulation, and lodge in the liver or lungs or, less frequently, in the brain, bone, or other organs. No adult worms are present in the gastrointestinal tract of humans. In tissue,E. granulosusoncospheres develop into cysts, which grow slowly (usually over many years) into large unilocular, fluid-filled lesions—hydatid cysts. Brood capsules containing numerous small infective protoscolices form within these cysts. Large cysts may contain>1 L of highly antigenic hydatid fluid as well as millions of protoscolices. Daughter cysts sometimes form in or outside primary cysts. If a cyst in the liver leaks or ruptures, infection can spread to the peritoneum. E. multilocularisproduces spongy masses that are locally invasive and difficult or impossible to treat surgically. Cysts occur primarily in the liver but can occur in the lungs, or other tissues. The cysts are not large, but they invade and destroy surrounding tissue and can cause liver failure and death. 