Echinococcosis (Hydatid Disease)

Adults of the dog tapeworm, Echinococcus granulosus, inhabit the intestinal tract of dogs. Sheep and cattle ingest the cysts in food contaminated by canine faeces. The cysts dissolve in the stomach and the liberated ova penetrate the intestinal wall. Dogs become infected by eating the viscera of dead, infected sheep and cattle, and the cycle is maintained . Man is an accidental dead-end host, infected by contact with contaminated dog faeces, and plays no role in the cycle of infection. After penetrating the bowel wall the embryos travel via the portal blood to the liver and other organs. They may die and calcify or they may slowly enlarge over many years, producing disease by pressure effects or rupturing into the peritoneal cavity or pleural space with dissemination of the larvae (scolices) and production of multiple new lesions .

The cysts can be visualized by ultrasonography or computed tomographic scanning or other imaging techniques , and serological tests may provide a specific aetiological diagnosis. In cases where treatment is required, surgical removal, marsupialization and sterilization of cyst contents with formalin, hypertonic sodium chloride or iodine solution, or therapy with anthelminthic agents such as mebendazole, albendazole or praziquantel, may be effective. Infection in dogs can be prevented by proper disposal of sheep and cattle carcasses.