To investigate the origin and dissemination of human T-cell lymphotropic virus type I in Latin America, we performed phylogenetic analysis on the LTR and env sequences of 13 HTLV-I isolates from Peruvians of four different ethnic groups: blacks and some mulattos of African origin; Quechuas of Inca origin; Nikkei of Japanese descendance; and Mestizos, a mixed population of white and Indian origin. All Peruvian samples could be situated within the cosmopolitan subtype HTLV-Ia, yet one sample showed an indeterminate Western blot pattern, lacking reactivity towards the HTLV-I type specific MTA1 peptide. Within the LTR, we could confirm the previously reported subdivision into four subgroups--one big transcontinental clade A, a Japanese clade B, a West African/Caribbean clade C and a North African clade D--and we identified a new separate subgroup E of black Peruvian strains. The clustering of the Peruvian samples seemed to depend on the ethnic origin of the host. The largest heterogeneity was observed in the black Peruvian samples. The mitochondrial DNA type of one of these black Peruvian strains of subgroup E was identical to that of West African source populations of the slave trade. Both findings support the idea of multiple post-Columbian introductions of African HTLV-Ia strains into the black Latin American population. Additionally, a tight cluster of Nikkei and Japanese samples implied a separate and rather recent transmission of a Japanese lineage of HTLV-I into Peru. A well-supported cluster of Latin American strains (including Peruvian Quechuas and Colombian Amerindians) could be situated within the transcontinental group. Molecular clock analysis of the Latin American and Japanese clade resulted in an equal evolutionary rate for those strains. Along with the anthropologically documented peopling of the Americas, the analysis was more in favour of a recent (400 to 100 years ago) introduction of HTLV-Ia into the American continent rather than a Palaeolithic introduction.
