HIV-1 genetic variability in Cameroon

In Cameroon, a central west African country, the first AIDS case was reported in 1985. Until 1991, the epidemic in Cameroon was considered to be ‘pre-epidemic', characterized by a seemingly low incidence of AIDS cases, compared with the rapid and most extensive spread of HIV in east and south Africa. During the past decade a marked epidemic was documented, with the number of AIDS cases doubling every year, until the cumulative number of AIDS cases reached 8141 in 1995 [1]. The relatively slow epidemic in Cameroon went together with a high diversity of HIV-1 group M subtypes A–H, circulating recombinant forms (CRF) CRF01.AE, CRF02.AG, and a relatively high prevalence of HIV-1 group O viruses [2]. Moreover, group N was also identified in Cameroon [3], as well as chimpanzees infected with HIV-1-related viruses sharing group N env sequences [4]. Although the spread of HIV-1 groups O and N is limited, group M viruses have significant public health importance. Knowledge of the genetic subtype as well as the intersubtype-recombinant nature of HIV-1 strains might be of crucial importance for the development of an HIV vaccine. Previous studies on HIV-1 variability in central west African countries indicated a very high diversity of different subtypes. As a consequence, these regions received major attention for surveillance studies in order to document on the relatively low sample numbers the range of variability that needs to be taken into account for vaccine development. From these studies we know that many different subtypes, A, B, C, D, F, G, H, CRF01.AE and CRF02.AG in group M, as well as group O strains, are circulating simultaneously in Cameroon [5–8]. Here we describe the HIV-1 group M distribution among samples, taken between November 1996 and April 1998, from individuals residing in different provinces in Cameroon. Cameroonian HIV-1-positive serum samples were collected from different geographical areas: centre (n = 11); littoral (n = 5); southwest (n = 11); northwest (n = 22); south (n = 17); and west (n = 8). These samples were taken from different target populations: blood donors (n = 6); sexually transmitted disease-infected individuals (n = 46); general cases (n = 15); AIDS suspects (n = 2); and pregnant mothers (n = 5). The screening of Cameroonian sera for HIV-1 group M/group O antibodies was performed either using Enzygnost Anti-HIV 1/2 Plus (Dade Behring, Marburg, Germany) or Vironostika HIV Uni-Form II plus O (Organon Teknika, Boxtel, the Netherlands). A total of 74 sera samples were successfully processed using reverse transcriptase–polymerase chain reaction (RT–PCR) for amplification of parts of gag and env. RNA extractions, one-tube RT–PCR and nested PCR were performed as reported elsewhere [5]. Subtyping was performed by gag heteroduplex mobility assay (HMA) [5] and env HMA [9]. Sixty-five out of 74 (88%) of the Cameroonian samples were either subtype A or CRF02.AG, as subtyped by env HMA, whereby differentiation between subtype A and CRF02.AG was not possible. These isolates were classified by gag HMA as follows: 46 (62.2%) CRF02.AG, 12 (16.2%) subtype A, three (4%) subtype G, three (4%) CRF01.AE, one (1.3%) subtype C. By parallel gag and env subtyping, the subtype distribution of the nine remaining samples was as follows: four subtype G, and one each of subtype C, subtype F (F2), CRF01.AE, and intersubtype recombinants G/B, CRF02.AG/G (Table 1). The low sample number did not allow us to make an association of subtype with origin or target populations.Table 1: Distribution of gag/ env subtypes in Cameroon. In addition to previous studies on molecular epidemiology in Cameroon, the current study highlights the fact that CRF02.AG and subtype A contribute substantially to the HIV epidemic in virtually all provinces in Cameroon. The epidemiological success rate of subtype A versus CRF02.AG is striking. Whereas subtype A is far more prevalent than CRF02.AG in east Africa, CRF02.AG is encountered in much higher numbers than subtype A in west Africa [2,5,10,11]. In central west Africa, both subtype A and CRF02.AG co-circulate in comparable amounts. Because the immunogen(s) included in a future HIV vaccine must be antigenically as close as possible to the most prevalent HIV-1 strains circulating in a particular geographical area, this study suggests the need to include at least subtype A as well as CRF02.AG-based immunogens into experimental vaccines, to be used in Cameroon. Leo Heyndrickxa Wouter Janssensab Peter M. Ndumbec Katleen Vereeckena Sandra Coppensa Kathleen De Houwera Katrien Fransena Gert Van der Auweraa Guido van der Groena