Schistosomiasis is an acute and chronic parasitic disease caused by blood flukes (trematode worms) of the genus Schistosoma. Transmission occurs when people suffering from schistosomiasis contaminate freshwater sources with excreta containing parasite eggs that hatch in water. Humans are infected when larval forms of the parasite – released by freshwater snails – penetrate the skin during contact with infested water. Schistosomiasis mostly affects poor and rural communities, particularly agricultural and fishing populations. Women doing domestic chores in infested water, such as washing clothes, are also at risk. Inadequate hygiene and contact with infected water make children especially vulnerable to infection.
There are two major forms of schistosomiasis – intestinal and urogenital – caused by five species of blood fluke. In the Western Pacific Region, intestinal schistosomiasis caused by Schistosoma japonicum is endemic in China and the Philippines, and that caused by Schistosoma mekongi is endemic in several districts of Cambodia and the Lao People’s Democratic Republic.
Symptoms of schistosomiasis are caused by the body’s reaction to the worms’ eggs. Intestinal schistosomiasis can result in 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.