The origin and evolution of human T-cell lymphotropic virus type II (HTLV-II) and the relationship with its replication strategy

In this review, the origin and evolution of the human T-cell lymphotropic v irus type II (HTLV-II) are discussed, with particular emphasis on its high genomic stability. In particular, it appears that the virus originated in t he African continent and has been infecting human populations for several t housands of years. The very low divergence accumulated on average between d ifferent viral strains during such a long period could be explained by cons idering that in infected individuals the viral amplification could be due m ainly to the clonal expansion of the infected cells, via cellular mitosis, rather than to reverse transcription. HTLV-II was introduced into the Ameri can continent during one or more migrations of HTLV-II-infected Asian popul ations over the Bering land bridge, some 15000-35000 years ago. Finally, du ring the last few decades, HTLV-II has been transmitted from native Amerind ians to injecting drug users (IDUs). It might be speculated that at least t wo separate introductions of HTLV-II in European IDUs from US IDUs have occ urred, due to the practice of needle-sharing among rDUs. (C) 1999 Elsevier Science B.V. All rights reserved.