Schistosomiasis with special references to the mechanisms of evasion

Schistosoma is a name derived from the Greek words (schisto means split and soma means body), because the body of male appears splitting longitudinally to produce a canal. Schistosoma is one of a trematoda but with separate sexes. Male is broader than the female and its lateral borders are curved ventrally forming long groove called gynaecophoric canal in which the female is held[1]. Schistosomes were formerly called bilharzia before Dr. Theodor Bilharz observed the worm firstly in the mesenteric veins of an Egyptian patient in 1851. The disease caused by this parasitic infection called bilharziasis or schistosomiasis. The disease is also called snail fever after its intermediate host, the fresh water snail[2]. Eggs of Schistosoma haematobium (S. haematobium) have been found in the renal pelvis of an Egyptian mummy dating back to the time of the 20th Dynasty (1250 to 1000 BC). Schistosoma antigens have been also identified by ELISA in Egyptian mummies of the Predynastic period (3100 BC)[3]. Schistosomiasis is a chronic parasitic infection which has been prevalent in the world for over 5 000 years. It is responsible for nearly 280 000 deaths per year with 200 million people worldwide being infected[2,4-8]. The geographical distribution of different species was shown in Figure 1.