Epidemiological Aspects and World Distribution of HTLV-1 Infection

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.

Reducing the global burden of HTLV-1 infection: An agenda for research and action

“…2). The current figure of 5e10 million HTLV-1-infected individuals is likely to be an underestimate by at least 2-fold (Gessain and Cassar, 2012). Even in high-income countries with a low prevalence of HTLV-1 infection, there is debate about the cost-effectiveness of universal HTLV-1 screening.…”

“…Review the global prevalence of HTLV-1 infection and identify opportunities and means to expand epidemiological studies Regions of high prevalence, including Indonesia, Iran, Africa, Japan, the Caribbean, South America (especially Brazil and Peru), Romania and parts of Australo-Melanesia and the Middle-East have been identified worldwide (Gessain and Cassar, 2012). Although HTLV-1 was discovered in 1979, there is no recommendation for systematic screening worldwide.…”

“…In principle, there is no major issue that would impair the development of a conventional preventive vaccine for HTLV-1: -HTLV-1 infection elicits vigorous humoral and cytotoxic responses that restrict viral replication, -subunit antigens are immunogenic and protect from infection, -purified recombinant antigens can easily be produced by conventional methods, and -worldwide genetic variation of the viral sequence is very limited (Gessain and Cassar, 2012).…”

“…This article presents the consensus views of taskforce members regarding unsolved or controversial issues that hamper further understanding of HTLV-1 and the development of new approaches for diagnosis, prevention and therapy. For additional information on the molecular mechanisms of pathogenesis, immunological aspects, epidemiology and currently available therapies for HTLV-1 infection, readers are referred to a number of excellent review articles (Bangham et al, 2015;Matsuoka and Jeang, 2007;Pique and Jones, 2012;Murphy, 2016;Gessain and Cassar, 2012;Kato and Akashi, 2015).…”

Epidemiology, clinical features, and outcome of HTLV-1–related ATLL in an area of prevalence in the United States

“…HTLV-1 infects up to 10 million people worldwide and is most endemic in southwestern Japan, the Caribbean, South America, and west Africa. 3 In America, the highest prevalence of HTLV-1 is found in Haiti, Jamaica, Dominican Republic, northeastern Brazil, and Peru. 3 South Florida is the continental US region most proximal to the Caribbean; therefore, HTLV-1-associated diseases, including ATLL and HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP), are commonly encountered in Miami, FL.…”