Micrograph of a human liver section showing the parasite Schistosoma mansoni (fluke). This is the major agent of schistosomiasis, a parasitic disease that infects humans. Although it has a low mortality rate, schistosomiasis often is a chronic illness that can damage internal organs and, in children, impair growth and cognitive development. The urinary form of schistosomiasis is associated with increased risks for bladder cancer in adults. Schistosomiasis is the second most socioeconomically devastating disease after malaria. This disease is most commonly found in Asia, Africa, and South America, especially in areas where the water contains numerous freshwater snails, which may carry the parasite. It affects many people in developing countries, particularly children who may acquire the disease by swimming or playing in infected water.