Chapter 3 : Schistosomiasis (Snail Fever)

Abstract:

Schistosomiasis is a waterborne parasitic worm infection affecting up to 400 to 600 million people in developing countries. Humans acquire schistosomiasis by direct contact with the larval stages (known as cercariae) that swim in freshwater. Prior to becoming cercariae, the immature developing and reproducing forms of these parasites spend a part of their life history living in various species of aquatic snails. Children and adolescents are at highest risk. All forms of chronic schistosomiasis are associated with anemia, undernutrition and growth impairments, poor school performance, and reduced productive capacity. Urogenital schistosomiasis caused by Schistosoma haematobium accounts for approximately two-thirds of the schistosome infections in Africa. This form is responsible for hematuria, female genital schistosomiasis, and squamous cell carcinoma of the bladder. Genital lesions increase the risk of HIV/AIDS transmission. Intestinal and liver schistosomiasis caused by S. mansoni accounts for approximately one-third of the cases in Africa and 1 million cases of schistosomiasis in Brazil. This form is responsible for bloody diarrhea, abdominal pain, and liver involvement (hepatomegaly and fibrosis). The major approach to control of schistosomiasis today is mass drug administration of praziquantel. It has led to the near elimination of schistosomiasis in some middle-income countries and to significant morbidity reductions in some sub-Saharan African countries.