Biomedical Engineering Reference
In-Depth Information
genera of Class Fasciolidae use freshwater snails as one of the intermediate
hosts (though some species have expanded their host range to include other
molluscans). Two polysyllabic diseases are caused by members of Class
Fasciolidae: fascioliasis and fasciolopsiasis.
Most cases of fascioliasis are caused by Fasciola gigantica (liver fluke
disease). This disease, common in Southeast Asia, occurs when a human
ingests metacercaria that contaminate vegetables. The metacercaria develop
in the small intestine, and eventually migrate to the biliary ducts of the liver.
The adult flukes lay eggs that are passed in feces. A variety of animals serve
as hosts for Fasciola gigantica, including cattle.
Fasciola hepatica, the sheep liver fluke, infects ruminants (particularly
sheep) but may also infect humans. Human infection occurs when metacer-
caria on vegetation (particularly watercress) are ingested.
Fasciolopsiasis is caused by Fasciolopsis buski, a large (up to 7.5 cm
length) fluke that lives in the intestines of the primary host (pigs and
humans). The number of humans infected is about 10 million. Surprisingly,
most infections are asymptomatic. Humans become infected by ingesting
metacercaria on vegetation. The disease occurs almost exclusively in
Southeast Asia and India.
Metagonimiasis is caused by any of several species of small flukes that
live in the small intestines of the primary host. The metacercaria cysts attach
to the underside of fish scales. Humans become infected when they eat
undercooked fish that contain the metacercaria. The disease occurs wherever
infected species of fish are eaten raw or uncooked. Most cases occur in Asia;
cases are particularly common in Korea.
Class Opisthorchiidae contains two infectious genera: Clonorchis and
Opisthorchis. Infectious genera within Class Opisthorchiidae produce the
condition known as opisthorchiasis, sometimes imprecisely called clonorch-
iasis, in which adult flukes live in the bile ducts of the liver. Humans become
infected after eating undercooked fish containing metacercaria.
Clonorchis sinensis, the Chinese liver fluke (also known as the Oriental
liver fluke), infects about 30 million people. As the name suggests, most
cases occur in Asia. Humans become infected when they eat uncooked or
raw fish infected with the metacercaria. The metacercaria develop in the
small intestine, and eventually migrate to the bile ducts. The adult flukes
live in the bile ducts. These flukes feed on bile produced by the liver,
excreted through the bile ducts and stored in the gall bladder. Hence, bile
does not reach the small intestine; and the normal digestion of food, in the
human host, is interrupted. Flukes in the liver produce a chronic inflamma-
tory response, and untreated infections may eventually lead to the develop-
ment of bile duct cancer (choledochocarcinoma and cholangiocarcinoma).
Opisthorchis felineus, the cat liver fluke, infects humans who eat under-
cooked fish containing the metacercaria. The adult fluke lives in the bile
ducts of the liver. Untreated infections may lead to cirrhosis (diffuse fibrosis)
Search WWH ::




Custom Search