Blood flukes, which make up the genus Schistosoma, are a type of parasitic flatworm that cause schistosomiasis, an infection that afflicts tens of millions of people a year. Schistosomiasis is in fact the second most socioeconomically harmful parasitic disease in the world, according to the World Health Organization. (Only malaria is more harmful.) Below we provide a brief guide and overview of blood flukes that includes the most essential information about this parasitic disease. We will also provide links to some of the best sources for information about blood flukes online.