Epidemioogical evidence of recent introduction of HIV-1 subtypes B and O into Nigeria

Abstract

Peptide based Enzyme Immuno-assay (PELISA) was used to determine HIV-1 subtypes circulating in Nigeria. The synthetic peptide used as the capture antigen were designed from the consensus sequence of the third hypervariable region (V3loop) of 6 HIV-1 subtypes namely A, B, C, D, E and O. A total of 925 ELISA reaactive and western blot confirmed HIV-1 positive plasma or serum samples collected over a 5 year period (1993-1997) from the three broad geographical (south-western, south-eastern and northern) regions of the country were analysed for the stduy. Specific antobodies to the six HIV_! subtypes were identified among the seropositive samples tested. There was an overall increase in the incidence of all the subtypes over the 5 years covered by this study. However, the prevalence of subtypes B and O was relatively low being 2.5% and 2.4% respectively. In addition, subtype B was not detected among HIV-1 positive samples collected before 1995. furthermore, subtypes B and O were not dtected in the samples from the south-eastern and northen regions respectively. Also, the incidence of subtypes B and O decreased with age while there was an increase in the incidence of subtypes E and D with age. On the ohter hand, the incidence of subtypes A and C did not vary significantly with age. Abesence of antibodies to HIV-1 subtypes B among blood samples from confirmed seropositive subjects that were collected during 1993-1994 together with low prevalence of subtypes B and O found in this study indicate their recent introduction. In addition, absence of antibodies to both subtypes in the south-eastern and northen regions respectively and decrease in thier incidence with age are convicing indications f recent introduction of both subtypes into Nigeria. There is therfore a need for continuous monitoring of HIV infection to identify appearance introduction of new variants of the virus into any particular geographical region.