Timing of the introduction into ethiopia of subcluster C ' of HIV type 1 subtype C

Viruses circulating in Ethiopia during the 1990s cluster with main subtype C, but a significant subcluster, C', was noted in multiple analyses. This s ubcluster of subtype C (C') was in a fifty-fifty equilibrium with the main subtype C (Abebe et al,, AIDS Res Hum Retroviruses 2000;16:1909-1914). To a nalyze genetic diversification within the subcluster of HIV-1 subtype C des ignated C' in the course of the epidemic in Ethiopia, we analyzed 165 env g p120 V3 sequences obtained between 1988 and 1999, We observed a highly sign ificant positive correlation between sampling years of individual sequences and their synonymous distances to the reconstructed common ancestor of the HIV-1 subtype C' subcluster. The extrapolation of the regression line of s ynonymous distances back to the date when no synonymous heterogeneity was p resent among the Ethiopian HIV-1 C' population allowed us to estimate 1982 (95% CI, 1980-1983) as the year of the onset of HIV-1 C' genetic diversific ation and expansion in Ethiopia, These results are in agreement with retros pective epidemiological and serological data, which demonstrated the absenc e of an HIV-1 epidemic in the Ethiopian population before the 1980s.