Schistosoma (mansoni,haematobium) is a neglected, but important pathogen in sub Saharan Africa parts of Asia, Egypt and South America, with an estimated 122 million infected, while 436 million are at risk of infection.
The infective stage of the parasite is shed by snail hosts that reside in water. The human parasitic stage inhabits the veins surrounding the bladder and genitals, and the host response to eggs released by the parasite can lead to complications including bladder cancer and kidney failure. Pathology caused by the parasite is also thought to play a role in facilitating transmission of HIV. Transmission is through human contact with contaminated water in areas where the host snail is found.
Treatment is available, but must be given annually to combat the cycle of infection and re-infection in endemic populations and there is little prospect of a safe anti-infection vaccine. However, recent studies have observed a form of natural immunity to the parasite in areas of high transmission that causes a reduction in the number of eggs laid by the parasite. This discovery raises the prospect of an anti-morbidity vaccine.