Schistosomiasis, also known as bilharzia or snail fever, is a chronic disease caused by parasitic worms that live in freshwater snails. According to the World Health Organization, schistosomiasis affects almost 240 million people worldwide, with the infection most prevalent in tropical and sub-tropical areas in poor communities without potable water and adequate sanitation. People most at risk include those in constant contact with water, such as fishermen, farmers, children and women whose domestic tasks bring them in contact with infested water. Schistosomiasis is the leading cause of mortality among the neglected tropical diseases.
Schistosomiasis infection is caused when people come into contact with water infested with water contaminated with the larval forms of the parasite, known as schistosomes. The parasite penetrates the body and develop into adult worms which live and multiply in blood vessels, which causes immune reactions and progressive damage to organs. Schistosomiasis spreads when an infected person urinates or defecates in or near freshwater, passing parasite eggs from the body to the water. In the water, the eggs hatch and infect freshwater snails, where they develop and then reemerge into the water as free-swimming larvae that can penetrate a person’s skin.
Symptoms of schistosomiasis are caused by the body’s reaction to the worms’ eggs. This can result in abdominal pain, diarrhea and blood in the urine or stool. Long-term damage includes chronic, irreversible diseases such as liver scarring, kidney failure and bladder cancer. The severity of infection depends on the amount of worms present and how long the person has been affected.
In children, the infection contributes to stunted growth, malnutrition, anemia and impaired cognitive development which disrupts school attendance and ability to learn, although the effects are usually reversible with treatment.
Schistosomiasis is diagnosed through the detection of parasite eggs in urine or stool specimens. Antibodies detected in blood or urine samples are also indications of infection.
Schistosomiasis can be treated with a single annual dose of the drug praziquantel. Treatment, paired with education and water, sanitation and hygiene (WASH) and snail control is essential for preventing the disease.
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