HIV-1 SUBTYPES AND TRANSMISSION
Diverse risk behaviors sustain HIV-1 transmission in different regions of the world, and within the same region, multiple transmission routes can be involved in spreading the epidemic. For example, in Eastern Europe and Central Asia in 2005, 67% of HIV infections were due to needle sharing among intravenous drug users (IDUs). In South and Southeast Asia, not including India, 49% of HIV infections reported were in commercial sex workers and their clients, while 22% were in IDUs. In Latin America, 26% of HIV infections were in men who have sex with men (MSM), and 19% were in IDUs (http://www.unaids.org/en/HIV_data/2006GlobalReport/default.asp). In Western Europe, unprotected intercourse among heterosexuals accounted for 45%, and among MSM, 28%, of HIV infections (http://www.eurohiv.org/reports/report_73/pdf/report_eurohiv_73.pdf).
As reported in the previous paragraph, the HIV-1 epidemic in these regions is sustained by different subtypes, and within each region, segregation of subtypes to different risk groups has been reported. For example, the cocirculation of subtype B among IDUs and CRF01_AE (originally defined as subtype E) among heterosexuals was originally described in Thailand (41); the segregation of subtype B to homosexuals and subtype C to heterosexuals was described in South Africa (126); more recently, two concurrent epidemics in Argentina have been reported, one among MSM, sustained by subtype B, and the other among heterosexuals and IDUs, sustained by BF recombinants (5). In Europe, where subtype B has sustained the HIV-1 epidemic among the “historical” IDU and homosexual risk groups, non-B subtypes and CRFs are progressively being introduced in association with increased heterosexual transmission of HIV-1 between migrants and/or immigrants from regions where HIV-1 is endemic and their European partners (19, 20, 121).
All these observations, reported at different phases of the HIV-1 epidemic around the world, may suggest different biological properties for the subtypes, resulting in their segregation among individuals with different risk behaviors for HIV-1 infection. Nevertheless, a consistent demonstration of this association has not been given. There is clearly no predetermined linkage between a specific subtype and a unique mode of transmission. In fact, subtype A is transmitted among heterosexuals in sub-Saharan Africa and IDUs in Eastern Europe; similarly, subtype B is transmitted among all the historical risk groups in Western countries.
Therefore, the apparent segregation of HIV-1 subtypes by type of risk behavior rather than as a result of virologic factors (cell tropism, coreceptor specificity) could derive from genetic, demographic, economic, and social factors that separate the different risk groups for HIV-1 infection. Moreover, the overwhelming predominance of the C subtypes in areas where unprotected heterosexual intercourse is the main transmission route could result from a founder effect with a fast-colonization outcome.
http://jvi.asm.org/content/81/19/10209.full