HUMAN IMMUNODEFICIENCY VIRUS TYPE-1 SEROTYPES AND SOME ASPECTS OF PHENOTYPIC PROPERTIES OF THE VIRUS ISOLATES IN NIGERIA

Abstract

Human Immunodeficiency Virus (HIV) is a retrovirus aetiologically and epidemiology associated with the Acquired Immunodeficiency Syndrome (AIDS). The prevalence of HIV infection and the disease and incidence of AIDS are on the increase in Nigeria. Ten different genetic subtypes (A-J) and an outlier group (0) of the virus have been identified. Hitherto, the different HIV-1 variants circulating in Nigeria has not been well determined. This study was designed to determine the predominant HIV-1 serotypes/subtypes in Nigeria and identify some of the important biological characteristics of the virus isolate in the country. A total of 925 confirmed HIV-1 positive samples were collected over a period of 5 years (1993-1997) from 8 states (Oyo, Lagos, Osun. Enugu, Rivers, Borno, Kaduna and Imo) in different geographical regions of Nigeria for this study. These sera or plasma samples were serotyped using the peptide based enzyme immuno-assay (PELISA). The peptide used as capture antigen were designed from the consensus sequence of the third hypervariable region (V₃ Loop) of subtypes A, B, C, D, E and O of HIV-1 . In addition, HIV- 1 strains were isolated by co-culture of Peripheral Blood Mononuclear Cells (PBMCs) from 45 confirmed HIV-1 seropositive individuals and pre-stimulated PBMCs from HIV-1 and HIV-2 seronegetive individuals. Cultures were observed for cytopathic effect and virus growth was monitored by detection of specific HIV-1 capsid protein (P24) in culture supernatant. The syncytium inducing ability of each isolate was determined by in vitro infection of MT-2 and MOLT-4 cell lines. The rate of virus replication was determined by time of firm detection of P24 antigen or appearance of CPE in the primary culture. Cell tropism was determined by infecting 5 different monocytie cell lines. Data were analysed using the Epi-Info programme. Specific antibodies to the six HIV-1 subtypes included the PELISA panel, were detected among infected persons in Nigeria with varying prevalence. Serotype C was the most prevalent, 48.3%(447) followed by A, 19.8%(183), D, 9.5%(88), E, 8.0%(74), B, 2.5%(23) and O, 2.45%(22). On the other hand, 36(3.9%) samples were dually reactive while 52(5.6%) seropositive samples did not react with any of the six antigens. Evidence of infections with all the serotypes except 13 was found in Nigeria through out the five years of the study. None of the samples collected in 1993 and 1994 reacted with specific scrotype B peptide antigen. Furthermore there was an overall increase in the incidence of each of the six serotypes over the study period. Out of the 45 samples cultured, 3 yielded HIV isolates. The isolation rate was higher among the symptomatic (24/28) than the asymptomaiic (12/17) individuals, but the difference was not significant (p=0.1251). Most of the isolates were fast replicating and syncytium inducing. In addition 31 of the 36 (86%) isolates replicated in more than one cell line. Correlation of HIV-1 subtypes and phenotypic characteristics showed that most of the isolates were fast replicating, syncytium inducing and pantropic irrespective of the subtype to which they belong. The results of this study show co-circulation or multiple HIV-1 subtypes and first evidence of infection with subtypes B, C, D and E in Nigeria. It also shows that HIV-1 subtype B may have been recently introduced into Nigeria and that most of the HIV-1 strains circulating in the country are highly virulent. In addition the study show that phenotypic characteristic such as syncytiurn inducing, replication rate and tropism (virulence) may not be solely related to specific subtypes of HIV-1.