Hydatid disease

Hydatid disease
(Hydatidasis or Hydatid cysts)
1- Hydatid disease is characterized by worldwide distribution and frequent hepatic involvement.
The incidence among human begins is dependent on the incidence in intermediate hosts including sheep, pig and cattle.
2- The most common unilocular hydatid cyst is caused by Echinococcus granulosus, while the alveolar type is caused by Echinococcus multilocularis.
Echinococcus granulosus:-
The adult of Echinococcus granulosus lives in small intestine of the dog. The worm measures up to 6mm long. It has a pyriform scolex provided with 4 suckers and with a double row of alternating rostellar hooks.
When eggs are swallowed by sheep, cattle or man, they hatch in the intestine and the hexacanth embryos migrate through blood and lymphatic channels to the liver and less frequently to other viscera.
Here they develop, rather slowly, into unilocular hydatids, characterized by their being spherical with inner germinal layer, surrounded in turn by thick circular and fibrous layers (cyst wall). In addition, broad capsules, which lack a protective cyst wall (contains only germinal layer) form from the inner germinal layer. Developing scolices are found within these structures. Each scolex, once fully developed, has the capability of developing into adult worm when present in the definitive host.
Usually the primary cyst has a dense layer of host connective tissues over the laminated membrane. Various daughter cysts (broad capsule) bud off from the inner germinal layer and remain attached or float free in the interior of the fluid filled cyst (as a bladder).
The individual scolices bud off from the inner wall of the daughter cysts are called hydatid sand.
Human are almost always dead-end intermediate hosts. When the intermediate host (except man) is eaten by dogs, the scolics are released into the GI, where they develop into adult worms. The adult consists of a scolex, small neek, and three prog. One at each developmental stage: immature, mature, gravids. The egg of Echinococcus granulosus resembles those of Taenia spp.