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 The 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 approximately 1.5 billion of individuals originating from known 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.

/pdf/epidemiological-aspects-and-world-distribution-of-htlv-1-56q6td07d0.pdf

Epidemiological Aspects and World Distribution of HTLV-1 Infection

https://www.thelancet.com/pdfs/journals/lancet/PIIS0140-6736(98)09460-4.pdf

Human T-lymphotropic virus type I infection

Evidence for human T cell lymphotropic viruses (HTLV) was sought in sera and cells collected from adults in 13 isolated South and Central American Indian tribes. Serologic tests identified frequent HTLV-II-like reactivity among the Cayapo and Kraho tribes, who live 330 km apart in Central Brazil. Polymerase chain reaction analyses of viral DNA in cell pellet and plasma fractions confirmed the virus as HTLV-II. Both tribes speak Ge and, at the time of blood collection (1974), subsisted as hunter/gatherers and slash and burn agriculturalists. Further testing of plasma from Cayapo and Kraho of all ages revealed overall HTLV-II prevalence rates of 33.3% and 12.2%, respectively, with increasing prevalence associated with age and female gender. These data reveal for the first time a high prevalence of HTLV-II infection in remote South American Indians with little contact with non-Indians. Thus, HTLV-II is postulated to be an ancient human virus in the New World.

Endemic human T cell lymphotropic virus type II infection among isolated Brazilian Amerindians.

To gain new insights on the origin, evolution, and modes of dissemination of human T-cell leukemia virus type I (HTLV-1), we performed a molecular analysis of 58 new African HTLV-1 strains (18 from West Africa, 36 from Central Africa, and 4 from South Africa) originating from 13 countries. Of particular interest were eight strains from Pygmies of remote areas of Cameroon and the Central African Republic (CAR), considered to be the oldest inhabitants of these regions. Eight long-term activated T-cell lines producing HTLV-1 gag and env antigens were established from peripheral blood mononuclear cell cultures of HTLV-1 seropositive individuals, including three from Pygmies. A fragment of the env gene encompassing most of the gp21 transmembrane region was sequenced for the 58 new strains, while the complete long terminal repeat (LTR) region was sequenced for 9 strains, including 4 from Pygmies. Comparative sequence analyses and phylogenetic studies performed on both the env and LTR regions by the neighbor-joining and DNA parsimony methods demonstrated that all 22 strains from West and South Africa belong to the widespread cosmopolitan subtype (also called HTLV-1 subtype A). Within or alongside the previously described Zairian cluster (HTLV-1 subtype B), we discovered a number of new HTLV-1 variants forming different subgroups corresponding mainly to the geographical origins of the infected persons, Cameroon, Gabon, and Zaire. Six of the eight Pygmy strains clustered together within this Central African subtype, suggesting a common origin. Furthermore, three new strains (two originating from Pygmies from Cameroon and the CAR, respectively, and one from a Gabonese individual) were particularly divergent and formed a distinct new phylogenetic cluster, characterized by specific mutations and occupying in most analyses a unique phylogenetic position between the large Central African genotype (HTLV-1 subtype B) and the Melanesian subtype (HTLV-1 subtype C). We have tentatively named this new HTLV-1 genotype HTLV-1 subtype D. While the HTLV-1 subtype D strains were not closely related to any known African strain of simian T-cell leukemia virus type 1 (STLV-1), other Pygmy strains and some of the new Cameroonian and Gabonese HTLV-1 strains were very similar (>98% nucleotide identity) to chimpanzee STLV-1 strains, reinforcing the hypothesis of interspecies transmission between humans and monkeys in Central Africa.

/pdf/molecular-epidemiology-of-58-new-african-human-t-cell-17yzhztode.pdf

Molecular epidemiology of 58 new African human T-cell leukemia virus type 1 (HTLV-1) strains: identification of a new and distinct HTLV-1 molecular subtype in Central Africa and in Pygmies.

Human T-lymphotropic virus type I (HTLV-I), the first human retrovirus to be discovered, was reported in 1980.' Shortly thereafter, its first disease association was established. Adult T-cell leukaemia/lymphoma (ATL), a lymphoproliferative malignancy first reported in Japan in 1977, was found to cluster in the same regions in Japan in which HTLVI is serological and virological evidence for an association between HTLV-I and ATL soon f o l l o ~ e d . ~ , ~ In 1985, a neurological disease, now called HTLV-I-associated myelopathy/tropical spastic paraparesis (HAM/TSP), was also found to be associated with HTLV-1.6 The closely related human T-lymphotropic virus type 11 (HTLV-11) was discovered in 1982 and was initially thought to be associated with hairy cell le~kaemia.~ Despite these early findings, the HTLVs remained relatively unknown until a third human retrovirus, now called human immunodeficiency virus type 1 (HIV-1), was discovered to be the cause of AIDS in 1984. Since that time, a great deal of attention has been focused on human retroviruses, including the earlier discovered HTLVs. The HTLVs have not only aroused considerable interest among researchers, but also entered the public health arena. Screening of volunteer blood donors for HTLV-I commenced in Japan in 1986 and is now performed in the United States, Canada, Trinidad and Tobago, the French West Indies and France. Because of these screening programmes and associated epidemiological studies, increasing numbers of persons infected with HTLVs are being identified. The purpose of this review is to describe the epidemiology of these viruses and the diseases they cause.

The Epidemiology of Human T-lymphotropic Virus Types I and II

Seroprevalence of human T-lymphotropic virus type 1 (HTLV-I) among a sample of persons selected from a government register of businesses in Trinidad was 3.2% in 1,025 persons of African descent compared to 0.2% among 487 persons of Asian descent and 0% among 46 persons of European-descent. In Tobago, from a coastal village, among persons of African ancestry ascertained as part of a cardiovascular survey, the rate was 11.4%, which was significantly higher when corrected for age and race than the rate in Trinidad. The seroprevalence rate of antibodies to hepatitis A and B was also significantly elevated in Tobago compared to Trinidad. HTLV-I seroprevalence rates were higher in females than males while hepatitis A and B rates were not significantly different in the two sexes. For males, age was a significant determinant of HTLV-I seropositivity, while for females, age, markers of poor sanitation, and hepatitis B were each independently linked to HTLV-I seropositivity. The frequent occurrence of multiple infectious exposures in persons of lower socioeconomic circumstances in this tropical environment may result in immune activation that heightens susceptibility to HTLV-I infection.

A study of HTLV-I and its associated risk factors in Trinidad and Tobago.

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A study of HTLV-I and its associated risk factors in Trinidad and Tobago.