schistosomiasis

schistosomiasis (shĭs`təsōmī`əsĭs), bilharziasis, or snail fever, parasitic disease caused by blood flukes, trematode worms of the genus Schistosoma. Three species are human parasites: S. mansoni, S. japonicum, and S. haematobium. The disease is prevalent in Asia, some Pacific islands, Africa, the West Indies, South America, Spain, Puerto Rico, and Cyprus. The larvae of the parasite are harbored by snails, which serve as intermediate hosts, and infect humans who bathe in or otherwise come in contact with infested waters. The larvae enter through the skin, migrate via the blood vessels, and mature in the lungs. From there they travel to the veins of the upper or lower intestine or bladder and reproduce. Some eggs pass out in the feces. Others are carried into the liver, where the body surrounds them with white blood cells, forming hundreds of tiny ball-like granulomas that eventually impair the liver's ability to function. It is believed that the flukes settle in blood vessels that have a particular human immune substance, tumor necrosis factor, that they require in order to reproduce.

The disease is characterized by a skin eruption at the site of entry, fever, diarrhea, and other symptoms, depending on the tissues affected; cirrhosis of the liver is common. The disease can be cured with the drug praziquantel, but reinfection can occur. Although symptoms vary according to the species of infecting fluke, all forms can result in general weakening and eventual death. Control of the disease is difficult, but attempts have been made to eradicate the snail hosts. Proper sanitation and disposal of human wastes are also important.

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schistosomiasis

 or bilharziasis

Group of chronic disorders caused by parasitic flatworms of the genus Schistosoma (blood flukes). Depending on the infecting species, thousands of eggs released by the females reach either the intestine or the bladder, are excreted in feces or urine, and hatch on contact with fresh water. The larvae invade snails, develop to the next stage, emerge into the water, and invade mammals to feed and breed in the bloodstream. An initial allergic reaction (inflammation, cough, late-afternoon fever, hives, liver tenderness) and blood in the stools and urine give way to a chronic stage, in which eggs impacted in the walls of organs cause fibrous thickening (fibrosis). This condition can lead to serious liver damage in the intestinal types and to bladder stones, fibrosis of other pelvic organs, and urinary-tract bacterial infection. In most cases, early diagnosis and persistent treatment to kill the adult worms ensure recovery.

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schistosomiasis

a disease caused by infestation of the body with blood flukes of the genus Schistosoma