Taeniid cestodes and sarcocystis of sheep

Sheep are the intermediate hosts of three cestode tapeworms of canids: Echinococcus granulosus, Taenia ovis and Taenia hydatigena. Each of these parasites exists as a tapeworm in the definitive host-dogs and other canids-and in a metacestode form in the intermediate host-sheep or other hosts. The metacestode form of T. ovis and T. hydatigena is a cysticercus, whilst for E. granulosus the intermediate stage is a hydatid cyst. T. ovis and, to a lesser extent, T. hydatigena, have a negative impact on the Australian meat industry, but neither presents any risk to the health of humans. E. granulosus infection in dogs is the primary source of hydatid infection in humans. Sheep are the principal source of E. granulosus infection for domestic dogs. Sarcocystis gigantea and S. medusiformis undergo sexual reproduction in the intestine of feral or domestic cats. Cats become infected by consuming sarcocysts in sheep meat. Lesions of sarcosporidiosis in sheep appear as small white cysts, resembling rice grains, in the oesophagus, tongue, diaphragm and striated muscles. They rarely have any effect on the health of the sheep but are commonly encountered when sheep are slaughtered. Heavy levels of infection lead to partial or total condemnation of carcases.