Abstract
The human T-cell leukemia virus type 1 (HTLV-1), identified as the first human oncogenic retrovirus 30 years ago, is not an ubiquitous virus. HTLV-1 is present throughout the world, with clusters of high endemicity located often nearby areas where the virus is nearly absent. The main HTLV-1 highly endemic regions are the Southwestern part of Japan, sub-Saharan Africa and South America, the Caribbean area, and foci in Middle East and Australo-Melanesia. The origin of this puzzling geographical or rather ethnic repartition is probably linked to a founder effect in some groups with the persistence of a high viral transmission rate. Despite different socio-economic and cultural environments, the HTLV-1 prevalence increases gradually with age, especially among women in all highly endemic areas. The three modes of HTLV-1 transmission are mother to child, sexual transmission, and transmission with contaminated blood products. Twenty years ago, de Thé and Bomford estimated the total number of HTLV-1 carriers to be 10–20 millions people. At that time, large regions had not been investigated, few population-based studies were available and the assays used for HTLV-1 serology were not enough specific. Despite the fact that there is still a lot of data lacking in large areas of the world and that most of the HTLV-1 studies concern only blood donors, pregnant women, or different selected patients or high-risk groups, we shall try based on the most recent data, to revisit the world distribution and the estimates of the number of HTLV-1 infected persons. Our best estimates range from 5–10 millions HTLV-1 infected individuals. However, these results were based on only approximately 1.5 billion of individuals originating from known HTLV-1 endemic areas with reliable available epidemiological data. Correct estimates in other highly populated regions, such as China, India, the Maghreb, and East Africa, is currently not possible, thus, the current number of HTLV-1 carriers is very probably much higher.
Highlights
Very rapidly after human T-cell leukemia virus type 1 (HTLV-1) discovery and its association with adult T-cell leukemia (ATL), several studies were initiated both by American and Japanese researchers, to get insights into the distribution, the transmission modes, as well as the origin of HTLV-1.as soon as 1982–1984, important works demonstrated clearly that Japan was a high endemic area for HTLV-1
Since the first studies, the geographic distribution of HTLV-1 carriers is quite uneven in Japan and the greatest prevalence is observed in Southwestern Japan (Kyushu island and the Okinawa archipelago)
Together with some early epidemiological studies showing an HTLV-1 seroprevalence in serum samples from inhabitants originating from different African countries, indicated that such a retrovirus was endemic in some areas of the African continent (Biggar et al, 1984; Hunsmann et al, 1984; Saxinger et al, 1984; de-The et al, 1985; de The and Gessain, 1986; Delaporte et al, 1989a,b, 1991; Ouattara et al, 1989; Verdier et al, 1989, 1994; Goubau et al, 1990; Dumas et al, 1991; Schrijvers et al, 1991)
Summary
Very rapidly after HTLV-1 discovery and its association with adult T-cell leukemia (ATL), several studies were initiated both by American and Japanese researchers, to get insights into the distribution, the transmission modes, as well as the origin of HTLV-1. ATL patients were reported in the Caribbean community living in the United Kingdom (Catovsky et al, 1982) Such data, together with some early epidemiological studies showing an HTLV-1 seroprevalence in serum samples from inhabitants originating from different African countries, indicated that such a retrovirus was endemic in some areas of the African continent (Biggar et al, 1984; Hunsmann et al, 1984; Saxinger et al, 1984; de-The et al, 1985; de The and Gessain, 1986; Delaporte et al, 1989a,b, 1991; Ouattara et al, 1989; Verdier et al, 1989, 1994; Goubau et al, 1990; Dumas et al, 1991; Schrijvers et al, 1991). Our main goal was to revisit the situation of HTLV-1 epidemiology, especially its world distribution, and its estimated prevalence This will be based on the current data, available in 2012, around 30 years after the first published epidemiological studies and nearly 20 years after the last estimation of global HTLV-1 prevalence. We shall try to present, with a table and a map, the HTLV-1 worldwide distribution and its prevalence estimates by continent and by country when possible
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