Perhaps behavioral differences between the two populatons (English and African) would also account for the diffence in HIV infecton rates.
Well, there seems to be more evidence for your point here: Key genetic factor in determining AIDS risk identified (http://www.freerepublic.com/focus/f-news/1316115/posts)
Note that "When the tests involved different population groups, the results revealed that persons of African-American origin had four copies of the CCL3L1 gene, whereas persons of European-American stock and Hispanic-Americans had two and three respectively."