scope:

Introduction.

a. General. The schistosomiases (known as Bilharzia disease or bilharziasis in parts of the world) have become recognized as among the more important diseases of man and certainly rank first among those resulting from helminthic infection. It has been estimated that approximately 5 percent of the world's population (over 150 million individuals) are infected by the three principal organisms causing the schistosomiases. These diseases are widely distributed geographically in Africa and adjacent areas, in the Carribbean Islands and South America, the Far East and recently indigenous cases of infection have been reported in Thailand. Although the schistosomiases are primarily diseases of native populations whose daily activities bring them into contact with fresh waters, it is obvious that these diseases assume considerable important and are of potential concern to military personnel.

b. Species. Human schistosomiases result from infection by one or more of three species of blood flukes; Schistosoma haematobium, S.mansoni, and S. japonicum. It should be realized, however, that other species of schistosomes may occur in these may infect man giving rise to swimmer's itch. Parasites of the genus Schistosoma belong to the class Trematoda, a part of the large phylum of flatworms, the Platyhelminthes. All schistosomes have a similar life cycle in which a snail serves as an obligatory intermediate host. The biology of the several species of schistosome carrying snails is sufficiently different to account for the differences in the epidemiology and control of the disease.