DIFFERENT EVOLUTION OF SIMIAN IMMUNODEFICIENCY VIRUS IN A NATURAL HOST AND A NEW HOST

To address the mechanisms of host-virus adaptation and pathogenesis of lentiviral infections, we compared the evolution of the same isolate of simian immunodeficiency virus (SIVsmm9) in two different situations : nonpathogenic infection of its natural host, the sooty mangabey, and AIDS-inducing infection of a new host, the rhesus macaque. Samples we re obtained at 6, 12, and 23 or 30 months postinfection from three ani mals of each species. Sequences were derived from the V1 and V2 domain s of the surface glycoprotein. In the macaques, we observed specific v ariations absent from all mangabey samples, indicating that different host species select different virus variants. In the macaques, we also observed a different shape in the phylogenetic tree, a lower divergen ce of sibling sequences, and a lower synonymous/nonsynonymous change r atio than in the mangabeys. This suggests that the viral population is larger and submitted to weaker selection pressures when host-virus ad aptation is achieved, such as in the mangabey. (C) 1998 Academic Press .