Echinococcosis (Hydatid Disease)

The hydatid diseases are caused by the cystic larval (metacestode) stages of cestodes of the genus Echinococcus. These parasites have life cycles involving two hosts. The adult tapeworms are found in the intestines of carnivores, the larval forms in the viscera of a variety of mammalian intermediate hosts. Transmission is often accomplished by the predator-prey relationship existing between the definitive and intermediate hosts. Humans and intermediate hosts become infected by ingesting eggs passed in the feces of definitive hosts. Four species are recognized: E. granulosus (Batsch, 1786); E. multilocularis Leuckart, 1862; E. oligarthrus (Diesing, 1862), and E. vogeli Rausch and Bernstein, 1972. The definitive and intermediate hosts as well as the characteristics of the disease produced in humans vary for each species (Table 1). Echinococcus granulosus, the cause of cystic hydatid disease, occurs worldwide and is of considerable public health and economic importance in some countries; E. multilocularis and E. vogeli cause the alveolar and polycystic forms of hydatid disease, respectively.