Hydatidosis: Dynamics of transmission

Hydatidosis is a widespread zoonosis infecting a large number of animals an d humans. Echinococcus granulosus has the smallest taenia adult of the cest odes but with the largest larva. Its morphologic and biologic features were identified with DNA analysis. Different strains were separated according t o the intermediate hosts: sheep, cattle, pigs, horses, camels. Definitive h ost are canids, mostly dogs, where the worm grows to adulthood in several m onths. The eggs are scattered in the pasture by wind and water and are inge sted by various hosts. The larvae migrate through the intestinal wall and p enetrate the organs; mostly liver and lungs. The eggs survive several days outside, depending on the temperature, but numerous eggs die in nature beca use they cannot resist desiccation and extreme temperatures. Dissemination is accomplished by dogs. In Turkana (Kenya) the incidence of hydatidosis is high because of the close relationship between the population and dogs and the habit of leaving their dead bodies in the grasslands. In rural areas, the custom of slaughtering sheep at home, among the dogs, is an important d issemination factor. The circumstances of transmission vary according to th e country. In Europe the natural life cycle of E. granulosus granulosus inv olves dogs as the definitive host and sheep as the intermediate host. In no rthern Europe E. granulosus borealis infects the canids and deer. E:. granu losus canadensis infects wolves and reindeer, but there are no human cases. In the endemic Mediterranean area, sheep and dromedaries are the intermedi ate hosts. In South America, the life cycle of E. granulosus develops among several definitive and intermediate hosts. Hence the dynamics of transmiss ion vary according to the countries with different hosts.