Genetic analysis reveals epidemiologic patterns in the spread of human immunodeficiency virus

The extreme variability of human immunodeficiency virus type 1 (HIV-1) make s it possible to conduct transmission studies on the basis of genetic analy sis and to trace global and local patterns in the spread of the virus. Two such patterns are discussed in this paper. First, in many European countrie s (e.g., Scotland and Germany), homosexual men tend to be infected with a s ubtly different variant of HIV-1 than intravenous drug users. In other Euro pean countries (e.g., Norway and Sweden), a distinction is also found betwe en the two risk groups; but based on available data, the distinction is a d ifferent one. The second pattern is a worldwide tendency for homosexual men in many different geographic regions around the world to carry HIV-1 subty pe B, the variant that is most prevalent in the Americas, Europe, and Austr alia. In contrast, people infected via other routes (mostly heterosexual co ntact) in those same countries carry a mixture of other subtypes, Biologic differences between the viruses infecting different risk groups have not be en found; the most likely explanation for the findings is different epidemi ologic patterns. Although data are still scarce, the authors attempt to use these patterns in the reconstruction of the worldwide spread of the HIV ep idemic.