Bilharzia (Schistomiasis) is present in the tropics and sub tropics. It is a worm infection the fully matured worms live in the bladder or intestines where they produce a large number of eggs. The eggs get passed out of the body in urine or stools and on contact with fresh water larvae hatch from the eggs. The larve then infect certain variates of snails where they develop and produce more larvae which are then released back into the water these larvae then penetrated the human skin.
Although it is not a killer disease it effects the general health. The most harmful effects are bleeding and ulceration of the intestine and bladder. Long term effects include liver damage, kidney failure and cancer of the bladder.
There is no vaccine available or being currently developed. The only real way to avoid getting bilharzia in an infected area is to avoid contact with fresh water. This is not really practical especially if you need to wash in rivers. The solution is to accept that you may get bilharzia from contact with water and go for a check up upon your return.
Flowing water is usually safer than still water, the larvae do not survive in salt, polluted or brackish water.
The cure is a single dose of Praziquantel tablets.