I gather one of the particular reasons that HIV is so widespread in Africa is because STDs are generally so common that it is typical for many men to have open sores on their genitalia, which can almost double HIV numbers, because unlike everywhere else, females can easily spread the disease to males.
Conversely, in China, there is a strong possibility that HIV infections are ignored among females, as part of the general disdain for females as a whole. This preference for males, especially for male children, has resulted in great imbalance in their male-female demographic balance, as couples are often eager to abort female children, in large part due to the 1-child per family rule.
all I can say is that Africa wasn't even supposed to have any people left after over 20yrs of the aids "crisis" and yet I think their population is very stable.