__Abstract__ Blood-dwelling parasitic trematodes (flatworms) of the genus Schistosoma cause the disease schistosomiasis or Bilharzia. There are 5 different Schistosoma species that infect humans and many other infecting different mammals. Over 200 million people worldwide are infected with schistosomes, mainly of the species S. haematobium, S. mansoni and S. japonicum. The disease is endemic in tropical areas and endemicity is dependent on the presence of the intermediate host, an aquatic snail, in fresh surface water. There is a strong variation in epidemiology between regions and localities, depending on local determinants such as irrigation or draining canals and human sanitary conditions