Symposium on Helminthiasis in Domestic Animals (EXCLUSIVE OF POULTRY)

Abstract

Among the earliest recognised abnormalities observed in slaughtered animals, were vesicles, fiUed with a clear watery-like fluid, which came to be caUed 'hydatids' or hydatid cyst. Many different kinds of cysts were originaUy called by that name but the term is now restricted to the larval forms of small tapewonns of the genus Echinococcus. This larval stage is -a serious and by .no means infrequent parasite of man. These tapeworms have a life cycle involving two hosts. The definitive host is a carnivore, usually a member of the family Canidae, while the intermediate host normally i~ a herbivore (usually an ungulate or a rodent), but while the definitive host is quite specific and the tapeworm stage is found only in carnivores, the larval stage is much less so and is found in man as well as a large variety of grass-eating animals. Because of the wide distribution of the Canidae ·and the presence of some suitable intermediate host in most parts of the world, the parasite has an almost cosmopolitan distribution (see map). The intensity of this distribution varies from place to place, being greatest where domestic herbivores are kept in numbers in close ·association with dogs and their relations, and where the dogs have opportunities to eat the cysts. Distribution is accordingly essentially determined by climate, vegetation, and human cultural practices.