The widening spectrum of primate T-lymphotropic viruses

Abstract

The first identified and most widespread of the Primate Tlymhotropic viruses (PTLV) are the human HTLV-I and simian STLV-I, present in a large number of Old World monkey and ape species. The fact that molecular genetic differences are more related to geographic origin than to host species indicate several interspecies transmissions among primates including man. Genomic analysis indicates two main groups, an African and an Australo-Asian, with long independent evolutions (t). The African group contains two HTLV-I clusters, a cosmopolitan, which spread over the world population, and a more localized central African cluster. In Africa many STLV-I group with the one or the other of these clusters, but very divergent STLV-I are also present, e.g. the STLVTAN90. The Australo-Asian group consists of the Melanesian HTLV-I and a number of divergent Asian STLV-I. The second PTLV is represented by HTLV-II. First thought to be a typical New World virus HTLV-II has now also been detected in autochtonous populations of Africa (2,3) and Mongolia. We identified a new type of PTLV, provisionally named PTLV-L, in a hamadryas baboon of north-eastern Africa (4). Its differences in nucleotide sequences from the types I and II are similar to that between the two known types. The genome organization of the pX region of the genome also differs from the other types (5). Recently we isolated another divergent PTLV from bonobos (pygmy chimpanzees), a species only living on the left bank of the Zaire river (6). At present the analysis of part of its genome in the env and pX regions indicates that it is more related to HTLV-II than to the other types, but is still very divergent from HTLV-II (7). The picture of PTLV that is emerging is that of slowly evolving viruses who have been present in Old World simians during much of their evolution. In the present view PTLVI would appear as the more successful type which spread to many species, and HTLV-II as the most specifically human PTLV.