Light micrograph of an adult male Schistosoma mansoni, a parasitic blood fluke that causes schistosomiasis (bilharzia). Fluke larvae live inside freshwater snails. The larvae leave their host when mature, and enter the water. They will penetrate human skin to reach the bloodstream, where they inhabit blood vessels of the intestine and bladder, releasing eggs into feces or urine to contaminate freshwater. This parasitic disease causes liver, kidney and bladder damage but can be treated with the drug praziquantel that kills the flukes. The female adult fluke (not visible) lives in a cleft below the male worm's head. 20x at 35mm.