High genetic diversity of HIV-1 strains in Chad, West Central Africa.

The genetic diversity of HIV-1 strains in Chad was documented with a total of 107 samples from patients attending the general hospital in N'Djamena, the capital city of Chad. The genetic subtypes were identified in the V3-V5 env and p24 gag regions by sequence and phylogenetic tree analyses. Of the 107 strains, 78 had the same subtype/CRF designation between env and gag. Four subtypes and three CRFs were found to cocirculate: subtype A, 20.5%; subtype D, 18.7%; CRF02_AG, 13.1%; CRF11_cpx, 13.1%; subtype G, 3.7%; CRF01_AE, 2.8%; and subtype F1, 0.9%. The remaining 29 strains (27%) had discordant subtypes or CRF designations between env and gag; in 15 of these 29 strains, a CRF was involved in the recombination event, and 10 were subtype G in gag and subtype A in env, forming a separate subcluster within subtypes G and A. Subtype D strains represent almost 20% of the HIV-1 strains circulating in Chad and form a separate subcluster in gag and env. Nearly full-length genome sequencing for two such strains (99TCD-MN011 and 99TCD-MN012) revealed that they represent nonrecombinant subtype D variants. Compared with neighboring countries, the genetic subtype distribution of HIV-1 strains in Chad is unique for several reasons: lower prevalence of CRF02, high prevalence of CRF11 and subtype D, and absence of CRF06. These data clearly show that subtype distribution is very heterogeneous in Africa, probably the result of different founder effects.