If you read a textbook it will tell you, these are the...

If you read a textbook it will tell you, these are the things, for instance, on the African continent that would contribute to immune deficiency: the various tropical diseases, which because of poor health infrastructure, poor nutrition, general levels of poverty, don't get treated; syphilis, untreated or not properly treated (which as I hear is a big problem, when it is treated and the symptoms disappear, but, in fact, it is not cured and incubates there) that will impact on the immune system. So you have got to deal with these things.