Geographic distribution of HTLV‐I and identification of a new high‐risk population

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Abstract
Epidemiologic studies indicate that human T‐cell lymphotropic virus type I (HTLV‐I), the causative agent of most cases of adult T‐cell leukemia/lymphoma (ATLL) in Southeast Japan and the Caribbean islands and the probable cause of a progressive neurological disorder often referred to as tropical spastic paraparesis, occurs with unusual geographic clustering. The current large‐scale serosurvey was undertaken to improve our understanding of HTLV‐I prevalence in different parts of the world. We analyzed 43,445 serum samples collected from various geographic locaies worldwide; 76% of these sera came from clinically healthy donors. Samples were initially screened by an enzyme‐linked immunosorbent assay (ELISA) and 4,353 were further evaluated by means of competition assays. In this study, which did not include sera from endemic areas of Japan, a high prevalence of infection was observed in several countries in the Caribbean basin. A significant age‐sex difference was observed between populations in the Caribbean and non‐endemic regions of Japan. The reason for the male excess in non‐endemic areas of Japan will require further study, while the female excess in the Caribbean basin is compatible with the previously described pattern for other HTLV‐I‐endemic areas. A newly recognized area of possible endemicity was southern Florida, where evidence of infection with HTLV‐I or a related virus was found in a group of native Americans whose sera were collected in 1968. In certain parts of the world, particularly sub‐Saharan Africa, important problems in determining specificity of reactivity occurred, probably because of cross‐reacting antibodies. No pattern was detected that could explain the cross‐reactivity solely on the basis of geographic areas, specific patterns of non‐viral parasitic infection, or methods of handling the specimens. It is possible that these cross‐reactivities are antibodies to proteins from HTLV‐I‐reiated retroviruses yet to be discovered.