Schistosomiasis also known as bilharziasis, is a chronic disease caused by past or present infection with parasitic blood flukes of any of five Schistosomaspecies: S. mansoni, S. japonicum, S. mekongi, S. intercalatum, or S. haematobium.
Symptoms and signs depend on the number and location of eggs trapped in the tissues. Initially, the inflammatory reaction is readily reversible. In the latter stages of the disease, the pathology is associated with collagen deposition and fibrosis, resulting in organ damage that may be only partially reversible. Central nervous system (CNS) involvement occurs because of embolization of eggs from the portal mesenteric system to the brain and spinal cord via the paravertebral venous plexus.
Two other species can infect humans: S. mekongi, found in Cambodia and Laos, and S. intercalatum, found in parts of Central and West Africa. These 2 species are rarely reported causes of human infection. Many countries endemic for schistosomiasis have established control programs, but others have not. Countries where development has led to widespread improvements in sanitation and water safety, as well as successful schistosomiasis control programs, may have eliminated this disease.