Schistosomiasis (bilharzia)

Schistosomiasis is an acute and chronic disease caused by parasitic worms. It is transmitted when larval forms released by freshwater snails penetrate human skin during contact with infested water.

Schistosomiasis is prevalent in tropical and subtropical areas of the world. It is more prevalent in poor communities without access to safe drinking water and adequate sanitation. It is estimated that at least 90% of those requiring treatment for schistosomiasis live in Africa.

Bilharzia is transmitted when people suffering from schistosomiasis contaminate freshwater sources with their excreta containing parasite eggs, which hatch in water. In the body, the larvae develop into adult worms. These worms live in the blood vessels where the females release eggs. Some of the eggs are passed out of the body in the faeces or urine to continue the parasite’s life cycle. Others become trapped in body tissues, causing immune reactions and progressive damage to organs.

There are two major forms of schistosomiasis: intestinal and urogenital. Both forms affect mainly poor and rural communities, particularly agricultural and fishing populations.

Intestinal schistosomiasis can cause abdominal pain, diarrhoea, and blood in the stool. Liver enlargement is common in advanced cases and is frequently associated with an accumulation of fluid in the peritoneal cavity and hypertension of the abdominal blood vessels. In such cases there may also be enlargement of the spleen.

The classic sign is presence of blood in urine (haematuria). Fibrosis of the bladder and ureter, and kidney damage are sometimes diagnosed in advanced cases. Bladder cancer is another possible complication in the later stages. In women, urogenital schistosomiasis may present with genital lesions, vaginal bleeding, pain during sexual intercourse, and nodules in the vulva. In men, urogenital schistosomiasis can induce pathology of the seminal vesicles, prostate, and other organs.

Women doing domestic chores in infested water, such as washing clothes in areas endemic for the disease, are greatly at risk. Women can also develop female genital schistosomiasis – which can cause genital lesions, vaginal bleeding, pain during sexual intercourse, and nodules in the vulva. Female genital schistosomiasis is also considered to be a risk factor for HIV infection, especially in women.

Lack of hygiene and certain play habits of school-aged children such as swimming or fishing in infested water make them especially vulnerable to infection. Schistosomiasis can also cause anaemia and stunting and a reduced ability to learn among children.

All forms of schistosomiasis can be treated effectively by the WHO-recommended medicine praziquantel. It is effective, safe, and low-cost. Even though re-infection may occur after treatment, the risk of developing severe disease is diminished and even reversed when treatment is initiated and repeated in childhood. As part of its global strategy to control the disease, WHO focuses on reducing the disease through periodic, targeted treatment with praziquantel through the large-scale treatment (preventive chemotherapy) of affected populations. This involves regular treatment of all at-risk groups.

Praziquantel is extremely safe and WHO recommends that pregnant women infected with the disease should be treated. But as a general precaution, WHO recommends treatment should be taken after the first trimester.

Tourists can easily avoid infection by not swimming in fresh water in areas where schistosomiasis is likely to occur. Even if infected, the worms do not cause a life-threatening disease for someone who is generally healthy. The disease is only serious for people living in endemic areas who become constantly re-infected and have no access treatment. If infected, treatment with praziquantel is easy, efficacious and safe.