As someone who grew up in KZN, I find the correlation interesting. Bilharzia is a significant issue (don't even think about swimming in the rivers unless you're in the Drakensberg mountains -- particularly in northern KZN where one also has the possibility of crocodiles deciding that you'll be a tasty morsel), and KZN is also the province with South Africa's highest HIV infection rate. Obviously, the correlation does not imply causation, but from the information presented in TFA, it's certainly plausible and, in my opinion, worth researching further.
I'm going to back those that have already posted that it's worth treating bilharzia in it's own right. If it contributes to a reduction in the HIV infection rate, so much the better.
Do not meddle in the affairs of troff, for it is subtle and quick to anger.