Background: HIV-2 seroreactivity has been previously reported in Nigeria, but HIV-2 has not been genetically confirmed.

Objectives: To determine the prevalence of HIV-2 infections and distribution of HIV-2 subtypes in persons infected with HIV-2 only and in those dually infected with HIV-1 and HIV-2 (HIV-1/2).

Methods: In 1999, we collected consecutive blood samples from 420 outpatients from 35 of 36 states in Nigeria. The plasma specimens were screened for the presence of HIV-1 and HIV-2 by ELISA. Specimens exhibiting any HIV-2-seroreactivity were tested with the INNO-LIA HIV Line Assay for further confirmation.

Results: Our data indicated that seroprevalence of HIV-2 was 5.5% (23 of 420), comprising 5% (21 of 420) HIV-1/2 dual and 0.5% (2 of 420) HIV-2 single infections. A PCR amplification using HIV type-specific protease primers, in conjunction with sequencing and phylogenetic analysis, confirmed the presence of HIV-2 in the 2 (100%) single-infection samples and HIV-1/2 in 11 (52%) of the 21 dually positive samples. In the remaining 10 HIV-1/2 seropositive specimens, only HIV-1 was identified. HIV-2 subtype A was found only in the HIV-1/2 dual infections, while HIV-2 subtype B was identified only in the HIV-2 single infections.

Conclusions: Our results suggest the segregation of HIV-2 subtype B and subtype A into HIV-2 single and HIV-1/2 dual infections, respectively. Larger studies are needed to better understand interaction of different HIV-2 subtypes with HIV-1 in persons with dual HIV-1/2 infections and to determine whether there are biological differences between HIV-2 subtype A and subtype B that might explain the observed segregation.