Schistosomiasis is a parasitic disease which infects over 200 million people in 74 countries in the developing world.
Schistosomes are small flukes which live in the bloodstream of infected people, mainly children.
Parasite eggs, passed in urine or faeces, hatch in contact with water to release free-swimming larvae which actively seek out and penetrate a particular kind of freshwater snail. After a period of multiplication within the snail, the parasites emerge and infect humans or other mammalian hosts by direct penetration through the skin. Many rural communities, which often lack adequate sanitation facilities and cleran water supplies, have daily contact with natural water bodies that harbour freshwater snails. In order to understand differences in the distribution, transmission and symptoms of schistosomiasis, we need to be aware of the genetic variability of both the parasites and their snail hosts. Research workers have been using information encoded within the DNA to differentiate forms of the parasite recovered from many parts of Africa, and to assess the relationships between schistosomes from different parts of the world.