Nigerian HIV type 2 subtype A and B from heterotypic HIV type 1 and HIV type 2 or monotypic HIV type 2 infections.

The presence of HIV- 2 in Nigeria has been confirmed serologically, but not genetically. To determine the frequency of HIV- 2 infections and the dynamics between HIV- 1 and HIV- 2 in 35 of 36 Nigerian states, 420 blood samples were collected in 1999. Antibodies to HIV- 1 and HIV- 2 were detected by EIA and seroreactivity was confirmed with the INNO- LIA HIV Line Assay. The frequency of HIV- 2 was 4.3% ( 18 of 420), with 3.8% ( 16 of 420) HIV- 1 and HIV- 2 ( HIV- 1/ 2) heterotypic and 0.5% ( 2 of 420) HIV- 2 homotypic infections. The presence of HIV- 2 subtype B in the two monotypic HIV- 2 infections and subtype A in 11 ( 68.8%) of 16 HIV- 1/ 2 dually seropositive samples was established by sequencing and phylogenetic analysis. HIV- 2 subtype B viruses were not found in any of the HIV- 1/ 2 dual infections, and HIV- 2 subtype A strains were not identified in either of the two monotypic HIV- 2 infections. Since our sample size was small and represented only convenience samples, larger randomized studies will be needed to better understand the dynamics of infection between HIV- 1 and different HIV- 2 subtypes and to determine whether significant biological differences exist among the HIV-2 subtypes.