On the other hand, they make big profits. In South Africa, children and rape victims are the chief pawns in this fight. One of the world's premier Aids conferences is to be held in Durban this year. Some researchers are so offended by Zuma's policies that they are lobbying to get her disinvited as a global slap in her face. The struggle should be interesting.
Scientists are baffled, and testing all sort of theories.
No one knows - but for some reason, Southern African peoples seem particularly vulnerable.