Travel and the introduction of human immunodeficiency virus type 1 non-B subtype genetic forms into Western countries.

Both high mutation rates and recombination contribute to the genetic diversity of human immunodeficiency virus type 1 (HIV-1). Among viruses of the main group, which are responsible for the HIV-1 pandemic, 21 circulating genetic forms have been reported, 11 of which are recombinant between > or = 2 subtypes. In Western Europe and the Americas, the HIV-1 epidemic is largely dominated by B subtype viruses; however, infections with diverse non-B subtype genetic forms are increasingly being recognized. In Western Europe and North America, most of them have been identified in immigrants or travelers returning from areas with high HIV-1 prevalence, mainly from sub-Saharan Africa and Southeast Asia, where non-B subtype genetic forms predominate, but propagation within other groups has been reported in some Western countries. This may have implications for prophylactic and therapeutic strategies and, by bringing in contact different genetic forms, may favor the generation of novel recombinant viruses. Travelers from different categories--including immigrants, military personnel, seamen, tourists, expatriates, diplomats, and businessmen--may be at risk of transporting HIV non-B subtype genetic forms to Western countries.