Abstract

PIP: The explosive spread of HIV-1 strain that infected approximately 75% of injecting drug users (IDUs) in early 1988 in Bangkok clustered phylogenetically with env subtype B viruses typically found in the Americas and Europe, but was genetically distinct from other subtype B strains. This strain was originally named Thai genotype B; hereafter it is referred to as subtype B'. An even more distinct strain, which infected a minority of IDUs but was found in about 90% of persons infected sexually, was referred to as subtype E. To explore the genetic characteristics of the strains of HIV-1 present during the early phase of the Thai epidemic, venous blood was collected in March 1992 from 13 consenting prison inmates. Proviral DNA was extracted from peripheral blood mononuclear cells, amplified using a nested polymerase chain reaction, and 345 nucleotides of the C2-V3 region of the env gene were sequenced. 10 of the 13 prisoners had HIV infections diagnosed in 1986 or 1987. The viral strains from these early HIV infections (THP01-THP10) were distinct from the subtype B' circulating in the general IDU population in Thailand in 1991. Phylogenetic analysis showed that these 10 sequences clustered with other subtype B strains in all 100 replicate trees, but were distinct from the subtype B' viruses. In contrast, the 2 prisoners diagnosed as HIV positive in 1988 and 1992 (THP11 and THP12, respectively) had typical subtype B' sequences containing the unique PLGPGOAW and HLGPGOAW V3 crown motif. The remaining prisoner, THP 13, was infected in 1989 with a subtype E virus. The explanation for the relative lack of spread of the subtype B strains (THP01-THP10) may be that the subtype B' and subtype E strains were introduced by chance into more dynamic, high-risk subgroups that spread the virus more rapidly. The subtype B' and subtype E strains may be also more easily transmitted in the Thai population than the pre-1988 subtype B strains.