Epidemiological 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-1subtypes 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 reactive 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
study.
Specific antibodies to the six HIV-1 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 detected in the samples
from the south-eastern and northern 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 other hand, the incidence of
subtypes A and C did not vary significantly with age.
Absence of antibodies to HIV-1 subtype B among blood samples from confirmed seropositive subjects that were
collected during 1993 and 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 northern regions
respectively and decrease in their incidence with age are convincing indications of recent introduction of both subtypes
into Nigeria. There is therefore a need for continuous monitoring of HIV infection to identify appearance/introduction
of new variants of the virus into any particular geographical region.
Key Words: HIV-1, Subtypes B and O, Nigeria
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 reactive 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
study.
Specific antibodies to the six HIV-1 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 detected in the samples
from the south-eastern and northern 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 other hand, the incidence of
subtypes A and C did not vary significantly with age.
Absence of antibodies to HIV-1 subtype B among blood samples from confirmed seropositive subjects that were
collected during 1993 and 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 northern regions
respectively and decrease in their incidence with age are convincing indications of recent introduction of both subtypes
into Nigeria. There is therefore a need for continuous monitoring of HIV infection to identify appearance/introduction
of new variants of the virus into any particular geographical region.
Key Words: HIV-1, Subtypes B and O, Nigeria
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