HYDATID DISEASE liver

HYDATID DISEASE
Introduction and pathology
Commonly called dog tape worm, hydatid disease is caused by Ecchinococcus granulosus. it is common in the tropics,
The dog is the definitive host and, as a pet, is the commonest source of infection transmitted to the intermediate hosts –humans, sheep and cattle. In the dog, the adult worm reaches the small intestine, and the eggs are passed in the faeces. These eggs are highly resistant to extremes of temperature and may survive for long periods. In the dog’s intestine, the cyst wall is digested, allowing the protoscolices to develop into adult worms. Close contact with the infected dog causes contamination by the oral route, with the ovum thus gaining entry into the human gastrointestinal tract. The cyst is characterised by three layers, an outer pericyst derived from compressed host organ tissues, an intermediate hyaline ectocyst which is non-infective and an inner endocyst that is the germinal membrane and contains viable parasites which can separate forming daughter cysts. A variant of the disease occurs in colder climates caused by Echinococcus multilocularis, in which the cyst spreads from the outset by actual invasion rather than expansion.