Schistosoma. Light micrograph (LM) of a circaria, the final larval stage of the blood fluke Schistosoma mansoni, the cause of schistosomiasis (bilharzia). Note the prominent forked tail. Adult flukes inhabit blood vessels of the small intestines, causing dysentery and diarrhoea. Their spiked eggs cause anaemia, inflammation and tissue scarring. The circariae (larvae) develop in freshwater snails (the intermediate host) and are released into the water. Humans (the final host) are infected while bathing or working in contaminated water. S. mansoni is widespread in Africa, the West Indies, and South and Central America. Magnification: x180 when printed at 10 centimetres wide