RESUMEN
We studied plasma samples from 2082 Mataco Indians living in 22 different communities in the western part of Formosa Province, northern Argentina. Samples were screened for HTLV-I/II antibodies by particle agglutination assay. All positive or borderline samples were then tested by an immunofluorescence assay (IFA) on C19 HTLV-II-producing cells. Western blot was used for confirmation of all IFA-positive plasma samples. The crude HTLV-II seroprevalence was 3.0% (62 of 2051), and 0.9% (5 of 588) in children less than 10 years old. The latter result suggests ongoing mother-to-child transmission, probably by breast feeding. There was a marked increase in HTLV-II seroprevalence with age (0.9%, 0-10 years; 1.6%, 11-20 years; 4.4%, 21-30 years; 3.4%, 31-40 years; 7.2%, 41-50 years; 5.7%, >50 years) in both male (p = 0.002) and female subjects (p = 0.00002). None of the 80 non-Indian inhabitants tested was HTLV-I/II seropositive. In a second study, among 105 Toba Indians from a village (Primavera) of the eastern part of this region, 23 were HTLV-II seropositive with a seroprevalence of 59% in those more than 40 years old. From seven of the Indians from Primavera, three others from neighboring regions (including two Tobas and one Pilaga), and one intravenous drug user (IVDU) from Rosario, DNA was extracted from peripheral blood mononuclear cells, and the gp21 transmembrane-encoding gene (590 bp) was amplified by PCR, cloned, and sequenced. LTR sequences were also obtained from the Pilaga, the IVDU, and one Toba. Molecular and phylogenetic analyses revealed that the Indians were all infected with closely related HTLV-II molecular strains belonging to the b subtype, while the IVDU was infected with an HTLV-II subtype a variant. Such data help to make a phylogenetic atlas of HTLV-II among Amerindian tribes and are crucial to gain new insights into the origin and modes of dissemination of this human retrovirus in the Americas.