Introduction and pathology

Introduction and pathology

• Hydatid disease is caused by Echinococcus granulosus, commonly called the dog tapeworm. The disease is globally distributed and, while it is common in the tropics, it is much less common in other countries; for example, in the UK the occasional patient may come from a rural sheep-farming community . The dog is the definitive host and 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 eg gs 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 an infected dog causes contamination by the oral route, with the ovum thus gaining entry into the human gas - trointestinal tract. The cyst is characterised by three layers: an outer peri - cyst , which is derived from compressed host organ tissues; an intermediate hyaline ectocyst , which is non-infective; and an inner endocyst , which is the germinal membrane and contains viable parasites that 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. Introduction and pathology

• Hydatid disease is caused by Echinococcus granulosus, commonly called the dog tapeworm. The disease is globally distributed and, while it is common in the tropics, it is much less common in other countries; for example, in the UK the occasional patient may come from a rural sheep-farming community . The dog is the definitive host and 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 eg gs 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 an infected dog causes contamination by the oral route, with the ovum thus gaining entry into the human gas - trointestinal tract. The cyst is characterised by three layers: an outer peri - cyst , which is derived from compressed host organ tissues; an intermediate hyaline ectocyst , which is non-infective; and an inner endocyst , which is the germinal membrane and contains viable parasites that 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. Introduction and pathology

• Hydatid disease is caused by Echinococcus granulosus, commonly called the dog tapeworm. The disease is globally distributed and, while it is common in the tropics, it is much less common in other countries; for example, in the UK the occasional patient may come from a rural sheep-farming community . The dog is the definitive host and 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 eg gs 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 an infected dog causes contamination by the oral route, with the ovum thus gaining entry into the human gas - trointestinal tract. The cyst is characterised by three layers: an outer peri - cyst , which is derived from compressed host organ tissues; an intermediate hyaline ectocyst , which is non-infective; and an inner endocyst , which is the germinal membrane and contains viable parasites that 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.