Echinococcus species

Abstract

Echinococcus spp. are the aetiological agents of hydatid disease, a zoonotic infection of worldwide distribution, in man and other intermediate hosts. Many questions regarding the factors which determine susceptibility/resistance to hydatid disease, and the factors which influence the viability and fertility of hydatid cysts, remain to be answered. Two species E.granulosus and E.multilocularis are principally responsible for human disease, although other species have been implicated. The definitive host for the former is the dog, with sheep or cattle acting as intermediate hosts following ingestion of contaminated dog faeces. Man is also infected coincidentally by contact with contaminated dog faeces. The eggs are extremely persistent in the environment. Following ingestion oncospheres penetrate the mesenteric vessels and are carried throughout the body, forming hydatid cysts mainly in the liver and lungs. These fluid filled cysts enlarge and contain numerous protoscolices, developed from an inner germinal layer within brood capsules, which may cause multiple daughter cysts within the peritoneum and adjacent organs if the cyst is ruptured. Most of the symptoms of echinococcosis arise from the compression of adjacent host structures by the gradually enlarging hydatid cyst. The preferred form of treatment is surgical removal of the intact cyst.