Chapter 3 : Schistosomiasis (Snail Fever)

Abstract:

Schistosomiasis is a waterborne parasitic worm infection affecting 207 million people in developing countries. Approximately 97% of the cases occur in the poorest regions of Africa. Humans acquire schistosomiasis by direct contact with the larval stages (known as cercariae) that swim in freshwater. Urinary schistosomiasis caused by Schistosoma haematobium is responsible for approximately 63% of the cases worldwide, while an intestinal and hepatic form caused by S. mansoni accounts for another 35%. Less than 1% of the global burden of schistosomiasis results from the Cold War warrior S. japonicum. Schistosome cercariae have a forked tail that allows them to swim and ultimately to directly penetrate human skin. Following skin penetration, the cercariae lose their tail and undergo a number of biochemical changes that allow them to resist attack by the human immune system. Today, the most effective means of controlling schistosome infections is mass drug administration of praziquantel to affected and at-risk human populations. Important future avenues of investigation include the potential effects of praziquantel mass drug administration on reducing HIV/AIDS transmission as well as the effect on schistosomiasis and anemia in pregnancy.