[A virus called HTLV-1. Epidemiological aspects].

GEOGRAPHIC DISTRIBUTION AND TRANSMISSION: HTLV-1 is not an ubiquitous virus. 15 to 25 million subjects are estimated to be infected. Endemic areas are recognized in southern Japan, tropical Africa, the Caribbean, some areas in Central and South America, and in few regions of the Middle East and Melanesia. In these endemic zones, 0.5 to 50% of the population, depending on age and gender, have specific antibodies against HTLV-1 antigens. Interhuman transmission can occur from mother to child by prolonged breast feeding, from men to women by sexual intercourse, and from blood exposure via infected lymphoid cells. MOLECULAR EPIDEMIOLOGY: Molecular epidemiology studies have evidenced several molecular types or genotypes of HTLV-1 linked to the geographical origin of the infected population rather than to the associated pathology (leukemia versus neuromyelopathy). The high stability of the HTLV-1 genome is probably related to clonal expansion of infected cells conjugated to the minimal use of the reverse transcriptase. This low variability has been used as a molecular tool to better understand the origin, the evolution and the dissemination of this retrovirus. The current distribution of HTLV-1, and its simian homologue STLV-1, results from at least 4 events: transmission of STLV-1 between different monkey species, transmission of STLV-1 to humans, persistence of HTLV-1 in isolated human populations, and finally global and more recent distribution of HTLV-1 (mainly the cosmopolite subtype) subsequent to migration of virus-infected populations.