THE PRESENCE OF A DIVERGENT T-LYMPHOTROPIC VIRUS IN A WILD-CAUGHT PYGMY CHIMPANZEE (PAN-PANISCUS) SUPPORTS AN AFRICAN ORIGIN FOR THE HUMAN T-LYMPHOTROPIC SIMIAN T-LYMPHOTROPIC GROUP OF VIRUSES

We isolated a divergent simian T-lymphotropic virus (STLV) (strain PP1 664) from a wild-caught African bonobo (pygmy chimpanzee, Pan paniscus ). Molecular and phylogenetic characterization of this virus show that it reliably separates from the two well-established primate T-lymphot ropic virus types, HTLV-I/STLV-I (PTLV-I) and PTLV-II, and from a thir d type isolated from an African-born Papio hamadryas and designated by us as PTLV-L. Four of eight bonobos kept at the Antwerp Zoo, Belgium, showed an aberrant PTLV serology. We amplified and sequenced a 709 bp PTLV proviral tax/rex fragment from one of the reactive bonobos. It d iffers by about 25% from the homologous nucleotide sequences of PTLV-I and PTLV-L and by about 17% from PTLV-II. This is comparable to the d ifferences among the three known types. Including the most divergent S TLV-I strains sequenced to date, for example, strain PHSu1 sequenced h ere, the divergence in this region within PTLV-I is less than 11% and within PTLV-II less than 4%. Although very divergent, this new bonobo STLV is the closest well-characterized simian relative of HTLV-II, rai sing the possibility of very divergent new HTLV strains. Our results s how that the number of PTLV types should be considered open and that t he variety of indigenous viruses in the PTLV group is greatest in Afri ca. Thus, as for the other primate retroviruses HIV and SIV, PTLV most probably has its origins in Africa.