Genetic subtypes of HIV-1 in the Philippines.

Objectives: To determine the genetic variability of HIV-1 amongst infected Filipinos and to analyze phylogenetic relationships, temporal introductions and transmission dynamics of identified variants.

Methods: Polymerase chain reaction amplification and direct sequencing of a 204 base-pair fragment of the env C2-V3 region from uncultured peripheral blood mononuclear cells obtained from 51 HIV-1-positive Filipinos infected from 1987 to mid-1996. Evolutionary distance and phylogenetic relationships among the DNA sequences were estimated.

Results: The 51 Philippine strains were classified into five env V3 subtypes, namely subtype B (n = 37), subtype E (n = 8), subtype A (n = 3), subtype C (n = 2) and subtype D (n = 1). The overall env nucleotide divergence ranged from 11.7 to 32.2%. The nucleotide variation appeared to be random and no temporal ordering was observed. The variation of the sequences at the tip of the V3 loop was very broad. Subtypes B and C isolates did not show close genetic relationship to other Asian variants. Only three of the subtype E strains had close affinity to known Asian sequences. The majority (94%) of the subjects acquired the infection by sexual transmission. About two-thirds were presumably infected outside the Philippines, whereas the remaining were infected indigenously. Information was limited to allow segregation of the identified subtypes by mode of transmission or risk groups.

Conclusion: Our findings demonstrate the presence of multiple genetic subtypes of HIV-1 in the Philippines. The apparent geographic range of previously reported genotypes in South and South-east Asia was extended and has obvious implications for env-based antiviral interventions.