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A search for human T lymphotropic virus (HTLV) types 1 and 2 and related viruses was performed by serological and molecular means on samples obtained from 421 adult villagers from the southern Cameroon forest areas. One individual (a 56-year-old Baka Pygmy hunter) was found to be HTLV-3 infected; however, there was a low proviral load in blood cells. Complete sequence analysis of this virus (HTLV-3Lobak18) indicated a close relationship to human HTLV-3Pyl43 and simian STLV-3CTO604 strains. Plasma samples from Lobak18, the HTLV-3 infected individual, exhibited a peculiar "HTLV-2-like" pattern on Western blot analysis and were serologically untypeable by line immunoassay. These results were different from those for the 2 previously reported HTLV-3 strains, raising questions about serological confirmation of infection with such retroviruses.

Human T-cell Leukemia virus type 1 (HTLV-1) and type 2 (HTLV-2) are pathogenic retroviruses that infect humans and cause severe hematological and neurological diseases. Both viruses have simian counterparts (STLV-1 and STLV-2). STLV-3 belongs to a third group of lymphotropic viruses which infect numerous African monkeys species. Among 240 Cameroonian plasma tested for the presence of HTLV-1 and/or HTLV-2 antibodies, 48 scored positive by immunofluorescence. Among those, 27 had indeterminate western-blot pattern. PCR amplification of pol and tax regions, using HTLV-1, -2 and STLV-3 highly conserved primers, demonstrated the presence of a new human retrovirus in one DNA sample. tax (180 bp) and pol (318 bp) phylogenetic analyses demonstrated the strong relationships between the novel human strain (Pyl43) and STLV-3 isolates from Cameroon. The virus, that we tentatively named HTLV-3, originated from a 62 years old Bakola Pygmy living in a remote settlement in the rain forest of Southern Cameroon. The plasma was reactive on MT2 cells but was negative on C19 cells. The HTLV 2.4 western-blot exhibited a strong reactivity to p19 and a faint one to MTA-1. On the INNO-LIA strip, it reacted faintly with the generic p19 (I/II), but strongly to the generic gp46 (I/II) and to the specific HTLV-2 gp46. The molecular relationships between Pyl43 and STLV-3 are thus not paralleled by the serological results, as most of the STLV-3 infected monkeys have an "HTLV-2 like" WB pattern. In the context of the multiple interspecies transmissions which occurred in the past, and led to the present-day distribution of the PTLV-1, it is thus very tempting to speculate that this newly discovered human retrovirus HTLV-3 might be widespread, at least in the African continent.

We studied 1508 individuals from Zaire, Burundi, Tanzania, Zambia, Kenya, and Cameroon for antibodies to HIV-2/HTLV-4. AIDS, ARC, other disease or tumor patients and healthy people were sampled from 1984-1986. By radioimmunoprecipitation and SDS/PAGE analysis and/or Western blot we failed to find any samples with specific antibodies to HIV-2/HTLV-4 indicative of infection. In contrast, 363 of these 1508 individuals demonstrated antibodies to HIV-1/HTLV-3B by the same serologic assays. HIV-2/HTLV-4 infection appears to be quite rare in Central Africa. AIDS and related syndromes in this study were exclusively correlated with HIV-1 infection. Studies in West Africa have shown high rates of infection with HIV-2/HTLV-4 where cases of AIDS are still relatively uncommon. These results indicate that HIV-2/HTLV-4 has a distinct geographic distribution from that of HIV-1 in Africa. Further studies are necessary to better define the pathogenicity and natural history of this distinct new virus, HIV-2/HTLV-4.