Schistosomiasis with special references to the mechanisms of evasion

Schistosomiasis is a disease caused by infection with Schistosoma spp. It affects 200 million people worldwide, especially in the developing countries. There are five known species of Schistosoma which currently infect humans in various geographical locations. Infection with Schistosoma spp. leads to two forms of the disease: acute and chronic. Chronic infection can affect various organs within the human body including the brain, lungs, gut and the reproductive organs, which leads to neuroschistosomiasis, pulmonary schistosomiasis, hepatointestinal schistosomiasis and urinary genital schistosomiasis, respectively. All Schistosoma spp. have a common denominator that they have the ability to infect, invade and evade the host’s immune mechanism. Schistosoma sp. is a very complex organism that requires two hosts, mollusk and mammalian, to survive, propagate and complete its life cycle. Hence, it has developed specific immune evasion mechanisms for each of them. Once Schistosoma sp. has infected and established itself within its mammalian host as an adult worm, it evades the immune mechanism of that host. However, the antigens released by the eggs can elicit an immune response with formation of granuloma around eggs. Granuloma formation is the main characteristic lesion in schistosomiasis, which in the liver can cause hepatomegaly in hepatointestinal schistosomiasis. This paper will summarize various immune responses against the parasite as well as varieties of strategies which developed by the Schistosoma spp. to persist within human hosts