Origin and Evolution of Human and Simian T-Cell Lymphotropic Viruses
Marco Salemi 1, Sonia van Dooren 1, Anne-Mieke Vandamme 1
1 NULL
*Correspondence: Anne-Mieke Vandamme, Email not available
Abstract
Three HTLV/STLV (together PTLV) types have been characterized: PTLV-I found in humans and most old world simian species, PTLV-II found in humans and pygmy chimpanzees and STLV-L only found in baboons. STLV-I clades and HTLV-I clades do not cluster according to species of origin, but rather according to geographic origin of the host. Within PTLV-I, the oldest phylogenetic lineages are found in Asian macaques, and the African HTLV-I subtypes Ib, Id, Ie and If have closely related simian relatives. The Melanesian/Australian HTLV-Ic and cosmopolitan Ia subtypes are also separated from the other subtypes by simian clades. Therefore, the different HTLV-I subtypes most probably each have a separate simian origin. HTLV-Ic most probably originated through interspecies transmission from Indonesian macaques to humans migrating to Melanesia and Australia around 50 000 years ago. The African human and simian T-cell lymphotropic lineages arose later as a consequence of host migrations from Asia to Africa. The transmission of Asian PTLV-I to African simians and humans, resulted in an explosive spread of this virus in Africa. The cosmopolitan HTLV-Ia, originating in Africa, was spread over the world due to post-Columbian human migrations. Within PTLV-II, human and simian viruses are phylogenetically well separated and it is not clear yet if interspecies transmissions took place within this PTLV type. Both clades have an African origin. Three HTLV-II subtypes exist, HTLV-IId is found in Efe pygmies from Congo and HTLV-IIa and IIb are found in Amerindian tribes, drug users and a few Africans. Most probably HTLV-IIa and IIb were brought from Africa to America as a result of the migrations of the human host over the Bering strait, 10 000 to 35 000 years ago, and were only recently introduced into injecting drug users. STLV-L also has an African origin, but whether PTLV originated in Africa or in Asia can not be concluded form the available information. What is clear now is that this T-cell lymphotropic virus repeatedly jumped from simians to humans, raising concerns about xenotransplantation.
