Schistosomiasis

Abstract

Schistosomiasis is a chronic helminth infection, caused by three different species of blood flukes—Schistosoma mansoni, S. japonicum, and S. haematobium—which afflicts more than 200 million people in Asia, Africa, the Caribbean, and South America. Man is infected on entry into contaminated fresh water by direct skin penetration of larvae emitted by the snail intermediate hosts. The young parasites (schistosomula) migrate from the skin to the lungs and through the liver to the final habitats of the adult worms in the venules of the intestines (S. mansoni and S. japonicum) or urinary bladder (S. haematobium). Since the schistosomes do not multiply within the definitive mammalian host, many individuals harbor relatively low worm burdens. Disease appears to be associated with intensity of infection and is due to the deposition of large numbers of parasite eggs in the host tissues, not only of the intestines and urinary bladder, but of the liver, lungs, ureters, and even the central nervous system.