Antibodies specific for human T-cell leukemia-lymphoma virus type I (HTLV-I) were demonstrated in serum samples from various groups of people in South Africa, Uganda, Ghana, Nigeria, Tunisia, and Egypt. The samples had been collected for other purposes and were presumably selected without bias toward clinical conditions associated with HTLV infections. Regional differences in antibody positivity were observed, indicating widely distributed loci of occurrence of HTLV on the African continent in people of both black and white ancestry. Two patients with high titers of antibody to HTLV-I had some signs of adult T-cell leukemia-lymphoma. In several groups a high frequency of false positive serum reactions was indicated when specific confirmation steps were included in the assay. Further characterization of these sera revealed highly elevated immunoglobulin levels, possibly due to polyclonal activation of immunoglobulin synthesis in these subjects. The possibility that related cross-reactive human retroviruses coexist in the same groups was not eliminated.

Fifty of 75 serum samples collected in the West Nile district of Uganda between August 1972 and July 1973 contained antibodies reactive with human T-cell leukemia (lymphotropic) virus type 3 (HTLV-III; mean titer, 601), while 12 of 75 samples were positive in a similar test for HTLV type 1 (HTLV-1) antibodies (mean titer, 236). The samples were screened by enzyme-linked immunosorbent assay and positive results were confirmed by a newly developed unlabeled antibody-peroxidase procedure with enhanced sensitivity for detection of antibody binding to immunoblots of HTLV-III antigen, demonstrating antibodies to proteins with molecular weights of 24,000, 41,000, and 76,000 in nearly all positive samples. Analysis of titration data indicated enhanced titers of antibody against HTLV-III and HTLV-I when coinfection occurred. The high prevalence and relatively low titers [compared to serum from patients with acquired immune deficiency syndrome (AIDS)] of antibodies recognizing HTLV-III proteins in sera from this population at a time that may predate or coincide with the appearance or spread of the AIDS agent (HTLV-III) suggest that the virus detected may have been a predecessor of HTLV-III or is HTLV-III itself but existing in a population acclimated to its presence. It further suggests an African origin of HTLV-III.