Silent mutation in the V3 region characteristic of HIV type 1 env subtype B strains from injecting drug users in the former Soviet Union

New independent states of the former Soviet Union are facing a rapidly growing epidemic of HIV-1 among injecting drug users (IDUs), This epidemic is caused by three HIV-1 populations, one belonging to HIV-1 subtype A (IDU-A), another to subtype B (IDU-B), and the third being a recombinant of the IDU-A and IDU-B,viruses (IDU-A/B, gagA/envB). Each of these populations is characterized by a high level of genetic homogeneity. We identified a unique synonymous nucleotide substitution in the first isoleucine codon at the (I) under bar HIGPGR motif (AT (T) under bar), which was observed in the env subtype B V3 sequences derived from IDUs in Russia and the Ukraine, This substitution was observed in none of 179 sequences obtained from IDUs in western Europe, northern America, and Asia. Molecular epidemiological analysis of HIV-1 strains based on this sequence pattern could be useful for tracing the origin and spread of the IDU-B viruses to other countries and risk groups.