Schistosomiasis (Bilhartziasis): Medical Advice from Jason Gibbs, Head Pharmacist at Nomad Travel Stores and Health Clinics
Gibbs, Jason, Geographical
This disease is most common in sub-Saharan Africa in particular Lake Nyasa--but areas of Brazil, China and other parts of Asia are also affected. It's mainly caused by three species of fluke--Schistoma haematobia, S.japonicum and S. mansoni. These all infect freshwater snails and humans as part of their lifecycle. Starting from the snail, tiny free-swimming parasites are released into the water, any one of which can penetrate human skin in just ten seconds. This can lead to an itchy rash around the area of penetration known as 'swimmers itch'.
Once through the skin, the parasites migrate to the venous system, and via the heart and lungs to the large veins around the intestines. In early infection, they may produce an allergic illness with fever, rash and malaise known as Katayama Fever. Once mature, the parasites move to their final resting sites in the body (which will depend on the infecting species)--the liver and intestine or the bladder and large bowel. It's from these sites that the mature worms, now in a permanently joined sexual pairing, release eggs that may be excreted by the infected individual and infect further freshwater sources and, consequently, more snails. It's also these eggs that cause an allergic reaction in the host and consequent complications.
Due to the parasites' different locations, each species causes its own set of symptoms. S. …