Echinococcus Granulosus is known as the minute tapeworm of dogs, or the hydatid tapeworm. The worm is about 4mm in lenght, and consists of a scolex bearing 4 sucker, numerous hooks, and 3 proglottids. Although not found, the eggs of E. granulosus are identical to those of Taenia sp.
Dogs acquire the infection by the ingestion of infective cysts in the tissue of herbivorous animals, such as sheep, which act as intermediate hosts. Each cyst contains a scolex, which develops into an adult tape worm. The adult tapeworm, which does not infect humans, resides in the small intestines of dogs and other canines. In humans, who act as intermediate rather than definitive hosts, this parasite cause unilocular hydatid cyst disease, an illness characterized by the presence of one or more cysts in a variety of tissues and organs of the body.
A hydatid cyst, which may reach the size of grape-fruit, has laminated outer layer, and an inner layer of germinal tissues from which the daughter cysts and brood capsules (smaller cysts containing several developing inverted scolices) bud. The cyst also contains loose pieces of germinal tissue and scolices. This is known as hydatid sand. In addition, there is a great deal of fluid inside the cyst.
Human acquire the infection by accidentally ingesting the eggs of E. granulosus, usually by hand-to-mouth contact with infected dog feces. The ingested eggs migrate to the various body tissues, and produce hydatid cysts. The life cycle is terminated at this point. Herbivores ingest the ova from pastures contaminated with dog feces.
Transmission & Pathogenesis
Human contract hydatid cyst disease by ingestion of Echinococcus Granulosus eggs, usually by hand-to-mouth contact with infected dog feces. Symptoms vary, depending on the location of the cyst in tissues. Although cysts may form in many areas of the body, the lung and the liver are most commonly affected. Pulmonary symptoms, such as cough, and chest pain, may develop with lung infection. One serious complication of hydatid cyst disease is the risk of anaphylatic shock, following rupture of the cyst.
The eggs of Echinococcus Granulosus are not found in human feces. The diagnosis of hydatid cyst disease may made by radiographic and serologic studies. A combination of assays, including enzyme immunoassay and immunoblot techniques, has been suggest to diagnose hydatid cyst disease. The demonstration of hydatid sand is also diagnostic.
Treatment & Prevention
Although surgical removal of hydatid cyst has long been considered the treatment of choice, several anti-helminthic agents are now available. These include praziquantel and mebendazole. Infection is prevented by good personal hygiene to prevent hand-to-mouth transmission of eggs from dogs to humans, avoidance of ingestion of sheep viscera by dogs, and anti-helminthic treatment of dogs, as necessary.