Luc Montagnier is the French scientist who received a Nobel Prize for discovering the HIV virus. In a recent interview, he makes a few surprising statements regarding the importance of immunity to prevent infection with HIV: http://www.youtube.com/watch?v=WQoNW7lOnT4.
HIV is a virus that is very difficult to transmit. One of the riddles has been how so many in Africa could be infected with it, when it is so hard to transmit. It has been shown that other infections will increase the likeliness of an HIV infection, and malaria is rampant in most parts of sub Saharan Africa! As well as many other infectious diseases. Also insufficient nutrition can contribute to low immunity, increasing the probability of an HIV infection.