A seroepidemiological survey of HTLV-1 in the Philippines.

The prevalence of human T-lymphotropic retrovirus type-1 (HTLV-1) was examined in the Asian Pacific area to search for endemic foci outside Japan. A total of 1323 sera from healthy subjects in the Philippines including Filipino lowlanders, Mongoloid slash-and-burn agriculturalists and the Mongoloid aboriginal hunter-gatherers (Aeta group and Mamanwa group) were examined for the presence of antibodies to HTLV-1 by the indirect immunofluorescence test and by the Western blot technique using HTLV-1 carrying cells. Nineteen out of 20 HTLV-1 antibody carriers found in the present study are clustered in the Aeta group of Mongoloid aboriginal hunter-gatherers who have until recently been isolated in the remote mountainous areas of Luzon Island since their arrival in the Philippines during the last glacial era (12,000-15,000 years ago). This finding supports the theory that HTLV-1 originated in Mongoloid racial groups during prehistoric times.