infectious diseases
Schistosomiasis
Etiology of Schistosomiasis
Schistosomiasis is by far the most important trematode infection.Schistosomais the only trematode that invades through the skin; all other trematodes infect only via ingestion. Over 200 million people are infected worldwide (seeCDC: About Schistosomiasis). Five species of schistosomes infect humans; all have similar life cycles involving freshwater snails.S. haematobiumcauses urinary tract disease; the otherSchistosomaspecies cause intestinal disease. Geographic distribution of schistosomes that infect humans differs by species: S. haematobium:Widely distributed over the African continent with smaller foci in the Middle East, Turkey, and India S. mansoni:Widespread in Africa, foci in Middle East, and the only species in the Western Hemisphere in parts of South America and some Caribbean islands S. japonicum:Asia, mainly in China, the Philippines, Thailand, and Indonesia S. mekongi:Southeast Asia S. intercalatum:Central and West Africa Humans are the main reservoir of infection. Dogs, cats, rodents, pigs, horses, and goats are reservoirs forS. japonicum, and dogs are reservoirs forS. mekongi. Transmission of these species does not occur within the United States (including Puerto Rico) and Canada, but the disease may be present in travelers and immigrants from endemic areas. 