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 i n Central and South America, and in few regions of the Middle East and Mela nesia. In these endemic zones, 0.5 to 50% of the population, depending on a ge and gender, have specific antibodies against HTLV-1 antigens. Interhuman transmission can occur from mother to child by prolonged breast feeding, f rom men to women by sexual intercourse and from blood exposure via infected lymphoid cells. Molecular epidemiology: Molecular epidemiology studies have evidenced sever al molecular types or genotypes of HTLV-1 linked to the geographical origin of the infected population rather than to the associated pathology (leukem ia versus neuromyelopathy). The high stability of the HTLV-1 genome is prob ably related to clonal expansion of infected cells conjugated to the minima l use of the reverse transcriptase. This low variability has been used as a molecular tool to better understand the origin, the evolution and the diss emination of this retrovirus. The current distribution of HTLV-1, and its s imian homologue STLV-1, results from at least 4 events: transmission of STL V-1 between different monkey species, transmission of STLV-1 to humans, per sistence of HTLV-1 in isolated human populations, and finally global and mo re recent distribution of HTLV-1 (mainly the cosmopolite subtype) subsequen t to migration of virus-infected populations.