Sequence and phylogenetic analyses of a new STLV-I from a naturally infected tantalus monkey from Central Africa.

Simian T-cell leukemia virus (STLV-I) is an oncovirus highly related to human T-cell leukemia virus type I (HTLV-I). To further examine the extent of variability, dissemination patterns, phylogeny, and evolution of these viruses, we analyzed a new STLV-I variant from a naturally infected Cercopithecus aethiops var. tantalus from the Central African Republic. Sequence analyses of its LTR, gag, pol, env, and pX (OrfII) genes indicated that this isolate, STLV-I (Tan 90), is 6% divergent from the prototype HTLV-I (ATK) and is the most divergent African STLV-I characterized to date. Our phylogenetic data indicate that southeast Asian and African STLV-I and HTLV-I strains segregated from each other thousands of years ago and that Japanese HTLV-I strains represent a relatively recent introduction of African or New World isolates. The data also indicate that interspecies transmission occurred several times on different continents over prolonged periods of time.