Human Retrovirus Research Articles

Structure Of The Single Health System For Diagnosis Of Htlv-1/2 In The Northern Region Of Tocantins

Background: The Human T-cell Lymphotropic Virus (HTLV), the first human retrovirus discovered, is associated with oncogenesis and is subdivided into several groups, with types 1 and 2 being the most prevalent and clinically relevant. Its main forms of transmission include unprotected sexual intercourse, blood transfusions, tissue and organ transplants, as well as vertical transmission (mother to newborn). In Brazil, mandatory testing for HTLV was implemented in the 1990s for blood donations and transplants, and expanded in 2024 by Ordinance No. 3,148 of the Ministry of Health, which includes testing during prenatal care. Objective: This study aimed to evaluate the structure of the Unified Health System (SUS) in the municipalities of the far north of Tocantins for the diagnosis of HTLV-1/2. Methodology: This is a qualitative study, in which semi-structured questionnaires were applied to Primary Care professionals and municipal health managers. Results: The results indicated significant deficiencies in knowledge of national protocols and the absence of a structured municipal flow for testing. Conclusion: It can be concluded that the health structure of the municipalities evaluated is insufficient for the effective diagnosis of HTLV-1/2

The relationship between SARS-CoV-2 infection and type 1 diabetes mellitus.

Environmental factors, in particular viral infections, are thought to have an important role in the pathogenesis of type 1 diabetes mellitus (T1DM). The COVID-19 pandemic reinforced this hypothesis as many observational studies and meta-analyses reported a notable increase in the incidence of T1DM following infection with SARS-CoV-2 as well as an association between SARS-CoV-2 infection and the risk of new-onset T1DM. Experimental evidence suggests that human β-cells express SARS-CoV-2 receptors and that SARS-CoV-2 can infect and replicate in β-cells, resulting in structural or functional alterations of these cells. These alterations include reduced numbers of insulin-secreting granules, impaired pro-insulin (or insulin) secretion, and β-cell transdifferentiation or dedifferentiation. The inflammatory environment induced by local or systemic SARS-CoV-2 infection might result in a set of signals (such as pro-inflammatory cytokines) that lead to β-cell alteration or apoptosis or to a bystander activation of T cells and disruption of peripheral tolerance that triggers autoimmunity. Other mechanisms, such as viral persistence, molecular mimicry and activation of endogenous human retroviruses, are also likely to be involved in the pathogenesis of T1DM following SARS-CoV-2 infection. This Review addresses the issue of the involvement of SARS-CoV-2 infection in the development of T1DM using evidence from epidemiological, clinical and experimental studies.

The incidence of HIV-2 infection in Spain is declining – a registry data analysis

ObjectivesHIV-2 infection is a neglected disease caused by a human retrovirus that causes AIDS more slowly than HIV-1. Infection with HIV-2 is endemic in West Africa. Given its differential features, guidelines recommend ruling out HIV-2 infection in all newly diagnosed HIV-seropositive individuals. MethodsA national registry of HIV-2 cases was created in Spain in 1989, following the first report of three HIV-2+ individuals in Barcelona. The main demographics, clinical, and virological data are reported up to December 2023. ResultsA total of 424 individuals with HIV-2 infection were recorded in the Spanish registry. After a peak in 2009 when 31 cases were reported, new HIV-2 diagnoses steadily decreased. Less than 10 cases/year have been notified since the COVID-19 pandemic. In 2023, only eight cases were reported.Mean age at HIV-2 diagnosis was 44 years old, ranging from birth to 83 years. A total of 265 (62.5%) were male. Migrants predominated, being 322 (76%) Sub-Saharan Africans; however, 60 (14.2%) were native Spaniards. Heterosexual exposure was the most likely route of infection in at least 287 (67.7%) cases. A few cases could be traced to transfusions (n = 4), vertical infection (n = 2), or injection drug use (n = 7). In addition, 15 individuals (3.5%) were men who had sex with men. Coinfection with HIV-1 was recognized in 39 (9.2%) individuals. Molecular characterization of HIV-2 subtypes was performed in 139 individuals, 121 being infected with subtype A and 18 with subtype B. ConclusionThe annual incidence of HIV-2 infection in Spain has decreased after peaking 15 years ago, being the current number of cases below 10 per year. Three-quarters are African migrants, and two-thirds are male. Circulation of HIV-2 in Spain is limited and steadily decreasing.

Human T-cell leukemia virus type 1 uses a specific tRNAPro isodecoder to prime reverse transcription.

Human T-cell leukemia virus type 1 (HTLV-1) is the only oncogenic human retrovirus discovered to date. All retroviruses are believed to use a host cell tRNA to prime reverse transcription (RT). In HTLV-1, the primer-binding site (PBS) in the genomic RNA is complementary to the 3' 18 nucleotides (nt) of human tRNAPro The human genome encodes 20 cytoplasmic tRNAPro genes representing seven isodecoders, all of which share the same 3' 18 nt sequence but vary elsewhere. Whether all tRNAPro isodecoders are used to prime RT in cells is unknown. A previous study showed that a 3' 18 nt tRNAPro-derived fragment (tRFPro) is packaged into HTLV-1 particles and can serve as an RT primer in vitro. The role of this tRNA fragment in the viral life cycle is unclear. In retroviruses, N1-methylation of the tRNA primer at position A58 (m1A) is essential for successful plus-strand transfer. Using primer-extension assays performed in chronically HTLV-1-infected cells, we found that A58 of tRNAPro is m1A-modified, implying that full-length tRNAPro is capable of facilitating successful plus-strand transfer. Analysis of HTLV-1 RT primer extension products indicated that full-length tRNAPro is likely to be the primer. To determine which tRNAPro isodecoder is used as the RT primer, we sequenced the minus-strand strong-stop RT product containing the intact tRNA primer and established that HTLV-1 primes RT using a specific tRNAPro UGG isodecoder. Further studies are required to understand how this primer is annealed to the highly structured HTLV-1 PBS and to investigate the role of tRFPro in the viral life cycle.

Abstract SY41-01: Selection of targeted neoantigens for personalized cancer vaccines

Abstract Neoantigen targeting personalized cancer vaccines (PCV) have the potential to revolutionize cancer treatment. These personalized vaccines rely on accurate epitope prediction and selection. We previously reported phase I trials of neoantigen targeting PCV in melanoma and glioblastoma multiforme (GBM). Recently we concluded a trial in renal cell carcinoma (RCC) where the neoantigen targeting PCV was immunogenic in all patients, targeted cancer drivers, and demonstrated in vitro reactivity to primary patient tumors. The neoantigen selection pipeline at DFCI supporting clinical trials utilizes immunopeptidome-trained epitope prediction algorithms to design synthetic long peptides as vaccine antigens containing predicted HLA Class I neoantigens. We also prioritize highly expressed neoantigens and neoantigens originating from cancer drivers as vaccine epitopes. For future iterations of this pipeline, we aspire to include novel classes of neoantigens originating from endogenous human retroviruses (ERV), fusion epitopes, novel or unannotated open reading frames (nuORFs), and immunopeptidome-identified neoantigens. The neoantigen selection pipeline is currently supporting multiple cancer vaccine trials at DFCI targeting melanoma, GBM, RCC, ovarian cancer, and chronic lymphocytic leukemia (CLL). Citation Format: Derin Keskin. Selection of targeted neoantigens for personalized cancer vaccines [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr SY41-01.

A Variety of Mouse PYHIN Proteins Restrict Murine and Human Retroviruses.

PYHIN proteins are only found in mammals and play key roles in the defense against bacterial and viral pathogens. The corresponding gene locus shows variable deletion and expansion ranging from 0 genes in bats, over 1 in cows, and 4 in humans to a maximum of 13 in mice. While initially thought to act as cytosolic immune sensors that recognize foreign DNA, increasing evidence suggests that PYHIN proteins also inhibit viral pathogens by more direct mechanisms. Here, we examined the ability of all 13 murine PYHIN proteins to inhibit HIV-1 and murine leukemia virus (MLV). We show that overexpression of p203, p204, p205, p208, p209, p210, p211, and p212 strongly inhibits production of infectious HIV-1; p202, p207, and p213 had no significant effects, while p206 and p214 showed intermediate phenotypes. The inhibitory effects on infectious HIV-1 production correlated significantly with the suppression of reporter gene expression by a proviral Moloney MLV-eGFP construct and HIV-1 and Friend MLV LTR luciferase reporter constructs. Altogether, our data show that the antiretroviral activity of PYHIN proteins is conserved between men and mice and further support the key role of nuclear PYHIN proteins in innate antiviral immunity.

Vulnerability to APOBEC3G linked to the pathogenicity of deltaretroviruses

Human retroviruses are derived from simian ones through cross-species transmission. These retroviruses are associated with little pathogenicity in their natural hosts, but in humans, HIV causes AIDS, and human T-cell leukemia virus type 1 (HTLV-1) induces adult T-cell leukemia-lymphoma (ATL). We analyzed the proviral sequences of HTLV-1, HTLV-2, and simian T-cell leukemia virus type 1 (STLV-1) from Japanese macaques (Macaca fuscata) and found that APOBEC3G (A3G) frequently generates G-to-A mutations in the HTLV-1 provirus, whereas such mutations are rare in the HTLV-2 and STLV-1 proviruses. Therefore, we investigated the mechanism of how HTLV-2 is resistant to human A3G (hA3G). HTLV-1, HTLV-2, and STLV-1 encode the so-called antisense proteins, HTLV-1 bZIP factor (HBZ), Antisense protein of HTLV-2 (APH-2), and STLV-1 bZIP factor (SBZ), respectively. APH-2 efficiently inhibits the deaminase activity of both hA3G and simian A3G (sA3G). HBZ and SBZ strongly suppress sA3G activity but only weakly inhibit hA3G, suggesting that HTLV-1 is incompletely adapted to humans. Unexpectedly, hA3G augments the activation of the transforming growth factor (TGF)-β/Smad pathway by HBZ, and this activation is associated with ATL cell proliferation by up-regulating BATF3/IRF4 and MYC. In contrast, the combination of APH-2 and hA3G, or the combination of SBZ and sA3G, does not enhance the TGF-β/Smad pathway. Thus, HTLV-1 is vulnerable to hA3G but utilizes it to promote the proliferation of infected cells via the activation of the TGF-β/Smad pathway. Antisense factors in each virus, differently adapted to control host cellular functions through A3G, seem to dictate the pathogenesis.

"It's Only a Model": When Protein Structure Predictions Need Experimental Validation, the Case of the HTLV-1 Tax Protein.

Human T-cell Leukemia Virus type 1 (HTLV-1) is a human retrovirus responsible for leukaemia in 5 to 10% of infected individuals. Among the viral proteins, Tax has been described as directly involved in virus-induced leukemogenesis. Tax is therefore an interesting therapeutic target. However, its 3D structure is still unknown and this hampers the development of drug-design-based therapeutic strategies. Several algorithms are available that can be used to predict the structure of proteins, particularly with the recent appearance of artificial intelligence (AI)-driven pipelines. Here, we review how the structure of Tax is predicted by several algorithms using distinct modelling strategies. We discuss the consequences for the understanding of Tax structure/function relationship, and more generally for the use of structure models for modular and/or flexible proteins, which are frequent in retroviruses.

Comprehensive Insight into the Functional Roles of NK and NKT Cells in HTLV-1-Associated Diseases and Asymptomatic Carriers.

Human T cell leukemia virus type 1 (HTLV-1) is the first human oncogenic retrovirus to be discovered and causes two major diseases: a progressive neuro-inflammatory disease, termed HTLV-1 associated myelopathy/tropical spastic paraparesis (HAM/TSP), and an aggressive malignancy of T lymphocytes known as adult T cell leukemia (ATL). Innate and acquired immune responses play pivotal roles in controlling the status of HTLV-1-infected cells and such, the outcome of HTLV-1 infection. Natural killer cells (NKCs) are the effector cells of the innate immune system and are involved in controlling viral infections and several types of cancers. The ability of NKCs to trigger cytotoxicity to provide surveillance against viruses and cancer depends on the balance between the inhibitory and activating signals. In this review, we will discuss NKC function and the alterations in the frequency of these cells in HTLV-1 infection.

Decoding dysregulated angiogenesis in HTLV-1 asymptomatic carriers compared to healthy individuals.

Human T-cell lymphotropic virus type 1 (HTLV-1) is the first identified human retrovirus responsible for two significant diseases: HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) and adult T-cell leukemia/lymphoma (ATLL). Although the majority of infected individuals remain asymptomatic carriers, a small percentage may develop ATLL or HAM/TSP. In tumorigenesis, a crucial process is angiogenesis, which involves the formation of new blood vessels. However, the precise mechanism of HTLV-1 associated angiogenesis remains unclear. This study aims to investigate the gene regulation involved in the angiogenesis signaling pathway associated with HTLV-1 infection. The research enrolled 20 male participants, including asymptomatic carriers and healthy individuals. Blood samples were collected and screened using ELISA for HTLV-1 confirmation, and PCR was performed for both Tax and HBZ for validation. RNA extraction and cDNA synthesis were carried out, followed by RT-qPCR analysis targeting cellular genes involved in angiogenesis. Our findings indicate that gene expression related to angiogenesis was elevated in HTLV-1 ACs patients. However, the differences in gene expression of the analyzed genes, including HSP27, Paxillin, PDK1, PTEN, RAF1, SOS1, and VEGFR2 between ACs and healthy individuals were not statistically significant. This suggests that although angiogenesis-related genes may show increased expression in HTLV-1 infection, they might not be robust indicators of ATLL progression in asymptomatic carriers. The results of our study demonstrate that angiogenesis gene expression is altered in ACs of HTLV-1, indicating potential involvement of angiogenesis in the early stages before ATLL development. While we observed elevated angiogenesis gene expression in ACs, the lack of statistical significance between ACs and healthy individuals suggests that these gene markers may not be sufficient on their own to predict the development of ATLL in asymptomatic carriers.

Human T-Cell Leukemia Virus Type 1 Oncogenesis between Active Expression and Latency: A Possible Source for the Development of Therapeutic Targets.

The human T-cell leukemia virus type 1 (HTLV-1) is the only known human oncogenic retrovirus. HTLV-1 can cause a type of cancer called adult T-cell leukemia/lymphoma (ATL). The virus is transmitted through the body fluids of infected individuals, primarily breast milk, blood, and semen. At least 5-10 million people in the world are infected with HTLV-1. In addition to ATL, HTLV-1 infection can also cause HTLV-I-associated myelopathy (HAM/TSP). ATL is characterized by a low viral expression and poor prognosis. The oncogenic mechanism triggered by HTLV-1 is extremely complex and the molecular pathways are not fully understood. However, viral regulatory proteins Tax and HTLV-1 bZIP factor (HBZ) have been shown to play key roles in the transformation of HTLV-1-infected T cells. Moreover, several studies have shown that the final fate of HTLV-1-infected transformed Tcell clones is the result of a complex interplay of HTLV-1 oncogenic protein expression with cellular transcription factors that subvert the cell cycle and disrupt regulated cell death, thereby exerting their transforming effects. This review provides updated information on the mechanisms underlying the transforming action of HTLV-1 and highlights potential therapeutic targets to combat ATL.

Serum Evaluation of Human T-lymphotropic Virus Type 1 and 2 (HTLV-I/II) and Human Immunodeficiency Virus (HIV) in Patients with Multiple Sclerosis (MS)

Background: Multiple Sclerosis (MS) is a multifactorial disease that causes neurological disability. Human retroviruses may have a role in the etiology of several acute and chronic neurological disorders. Objectives: We aimed to investigate the presence of HTLV-I/II and HIV antibodies in the sera of MS patients to assess the relationship between these infections and MS. Methods: This case-control study was conducted on serum samples of MS patients and individuals admitted to the same hospital with no symptoms of MS as the control group. Samples were examined for HIV and HTLV-I/II antibodies using ELISA kits. Results: A total of 79 people, including 38 MS patients and 41 healthy individuals, were evaluated. The frequency of HIV antibodies was 0.0% in both the case and control groups. The HTLV-I/II antibodies were detected in 1 patient in the control group and no patients in the MS group, with no statistically significant difference between the two groups (P: 0.999). Conclusions: This study could not establish a relationship between the presence of HTLV-I/II or HIV antibodies and MS.

Interplay between endogenous and exogenous human retroviruses.

In humans, retroviruses thrive more as symbionts than as parasites. Apart from the only two modern exogenous human retroviruses (human T-cell lymphotropic and immunodeficiency viruses; HTLV and HIV, respectively), ~8% of the human genome is occupied by ancient retroviral DNA [human endogenous retroviruses (HERVs)]. Here, we review the recent discoveries about the interactions between the two groups, the impact of infection by exogenous retroviruses on the expression of HERVs, the effect of HERVs on the pathogenicity of HIV and HTLV and on the severity of the diseases caused by them, and the antiviral protection that HERVs can allegedly provide to the host. Tracing the crosstalk between contemporary retroviruses and their endogenized ancestors will provide better understanding of the retroviral world.

The Pleiotropic Effects of YBX1 on HTLV-1 Transcription.

HTLV-1 is an oncogenic human retrovirus and the etiologic agent of the highly aggressive ATL malignancy. Two viral genes, Tax and Hbz, are individually linked to oncogenic transformation and play an important role in the pathogenic process. Consequently, regulation of HTLV-1 gene expression is a central feature in the viral lifecycle and directly contributes to its pathogenic potential. Herein, we identified the cellular transcription factor YBX1 as a binding partner for HBZ. We found YBX1 activated transcription and enhanced Tax-mediated transcription from the viral 5' LTR promoter. Interestingly, YBX1 also interacted with Tax. shRNA-mediated loss of YBX1 decreased transcript and protein abundance of both Tax and HBZ in HTLV-1-transformed T-cell lines, as well as Tax association with the 5' LTR. Conversely, YBX1 transcriptional activation of the 5' LTR promoter was increased in the absence of HBZ. YBX1 was found to be associated with both the 5' and 3' LTRs in HTLV-1-transformed and ATL-derived T-cell lines. Together, these data suggest that YBX1 positively influences transcription from both the 5' and 3' promoter elements. YBX1 is able to interact with Tax and help recruit Tax to the 5' LTR. However, through interactions with HBZ, YBX1 transcriptional activation of the 5' LTR is repressed.

HTLV-1 and blood donation.

Human T-cell leukaemia virus type 1 (HTLV-1) is a human retrovirus that causes adult T-cell lymphoma and HTLV-associated myelopathy. In this issue, Rosadas et al. use data from a recent WHO report to describe how blood banks test for HTLV-1 and how this testing contributes to public health surveillance for the virus. Commentary on: Rosadas et al. HTLV-1 screening of blood donations: we are systematically missing opportunities. Br J Haematol 2023;202:1220-1223.

RFS Proudly Announces the 2022 Award Recipient for AIDS Research and Human Retroviruses.

RFS Proudly Announces the 2022 Award Recipient for AIDS Research and Human Retroviruses.

Immune Responses to the human retroviruses HIV-1 and HTLV-1

Retroviruses are viruses that integrate their reverse transcribed cDNA into the host genome. Integration into the host DNA ensures their replication and generation of new viral particles. In this minireview I will focus on the interaction of two huma retroviruses with the immune system. Both human immunodeficiency virus type 1 (HIV-1) and the human T cell leukemia virus are retroviruses that target the CD4+ T lymphocytes. The CD4 T lymphocytes play a central role in the immune system and help coordinate the immune response by stimulating other immune cells, such as macrophages, B lymphocytes, and CD8 T lymphocytes, to fight infection. HIV-1 weakens the immune system by destroying CD4 T cells resulting in acquired immunodeficiency syndrome (AIDS). In contrast, HTLV-1 infection results in the transformation of these cells causing human T cell leukemia.

Abstract 6219: Endogenous human retroviruses in epithelial ovarian cancers: An exploratory analysis

Abstract Objectives: Endogenous human retroviruses (ERVs) are remnants of exogenous retroviruses that gained access to germline cells allowing integration into the human genome. Emerging data suggest that some ERVs may become activated allowing epigenetic alterations through DNA methylation or histone modification, which can further alter gene regulation. This may serve as a targeted therapeutic opportunity in modulating oncogenesis, through aberrant oncogene activation or tumor suppressor gene inactivation. This is an emerging area of exploration in ovarian cancer. Methods: We applied our ERV mapping tools (1) to RNA-seq data from 24 female patients with ovarian, fallopian tube, or primary peritoneal cancers to investigate expression of ~550,000 ERV elements from the Human Endogenous Retrovirus database (HERVd) (2, 3). Univariate Cox regression models were constructed with normalized ERV expression data and the most significantly differentially expressed ERVs were then filtered using a penalized Lasso-Cox proportional-hazards model. ERV expression, alongside the available clinical data (including age, histotypes, and tumor stage) were provided as inputs and linear predictors generated by the model separated samples into either high or low risk categories. We identified a panel of 15 predictive ERVs and these risk evaluations allowed for Kaplan-Meier analyses of survival by clinical parameters alone versus combined with ERV signature. We also performed a secondary analysis of platinum resistant ovarian cancers using RNA-seq data (GSE102118) to investigate the effect of demethylating agent guadecitabine on ERV expression (n=9) (4). Results: Exploratory analyses of ERVs demonstrated significantly different expression between histologies (clear cell, mucinous, endometrioid, high grade serous) and FIGO disease stage. In our prognostic model, Kaplan-Meier survival analysis using only clinical parameters resulted in a significance level of 0.0013, however the supplemented model combining the 15-ERV panel and the clinical data discriminated the two risk groups for time to recurrence at a much higher significance level of p = 7.076 × 10−8. Included in the 15 ERV panel are HERVK, HERV3, and several putative ERV promoters including LTR12, LTR7, LTR3 and LTR4 (5). In our secondary analysis of platinum-resistant patients, the ERV transcripts were compared for each patient pre- and post-guadecitabine treatment and there were several ERVs with risk-predictive values induced in patients receiving guadecitabine including LTR7, LTR12 and HERVK. Conclusions: In summary, ERV RNA expression in ovarian cancer is significantly different between histologies and disease stages. The ability to successfully classify patients as either high-risk or low-risk for disease progression is of considerable value for patient management and ERVs may improve prognostication and guide future therapeutic targeting. Citation Format: Jill Alldredge, Vinay Kumar, Brook Sanders, Farahnaz Rahmatpanah. Endogenous human retroviruses in epithelial ovarian cancers: An exploratory analysis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6219.

Research on HTLV-1 and HTLV-2 in Latin America and the Caribbean over the last ten years

Worldwide, Human T-lymphtropic virus-1 and 2 (HTLV-1 and 2) infects approximately more than 10 million people, mostly occurring in hyperendemic areas such as the region of Latin America and the Caribbean (LAC). A comprehensive bibliographic exploration of original articles published on the Web of Science Core Collection database over the last 10 years was done. A bibliometric analysis was performed using the bibliometrix package in RStudio and VOSviewer. A total of 519 articles published in 194 journals were identified along the 10 years studied. In 2012 the peak number of publications was identified and the average number of citations per document was 1.33. Galvao-Castro B was the author with the greatest number of publications. Aids Research and Human Retroviruses was the most productive journal, and the study by Bangham CRM was the most cited. Brazil was the country with most corresponding authors that had the most publications and the most significant number of total citations. Infections and HTLV-1 were the most used keywords. In conclusion, according to the current quantitative analysis, there is a need for more significant promotion of research on HTLV-1 and 2 among the scientific community of LAC.

Geographic distribution, clinical epidemiology and genetic diversity of the human oncogenic retrovirus HTLV-1 in Africa, the world's largest endemic area.

The African continent is considered the largest high endemic area for the oncogenic retrovirus HTLV-1 with an estimated two to five million infected individuals. However, data on epidemiological aspects, in particular prevalence, risk factors and geographical distribution, are still very limited for many regions: on the one hand, few large-scale and representative studies have been performed and, on the other hand, many studies do not include confirmatory tests, resulting in indeterminate serological results, and a likely overestimation of HTLV-1 seroprevalence. For this review, we included the most robust studies published since 1984 on the prevalence of HTLV-1 and the two major diseases associated with this infection in people living in Africa and the Indian Ocean islands: adult T-cell leukemia (ATL) and tropical spastic paraparesis or HTLV-1-associated myelopathy (HAM/TSP). We also considered most of the book chapters and abstracts published at the 20 international conferences on HTLV and related viruses held since 1985, as well as the results of recent meta-analyses regarding the status of HTLV-1 in West and sub-Saharan Africa. Based on this bibliography, it appears that HTLV-1 distribution is very heterogeneous in Africa: The highest prevalences of HTLV-1 are reported in western, central and southern Africa, while eastern and northern Africa show lower prevalences. In highly endemic areas, the HTLV-1 prevalence in the adult population ranges from 0.3 to 3%, increases with age, and is highest among women. In rural areas of Gabon and the Democratic Republic of the Congo (DRC), HTLV-1 prevalence can reach up to 10-25% in elder women. HTLV-1-associated diseases in African patients have rarely been reported in situ on hospital wards, by local physicians. With the exception of the Republic of South Africa, DRC and Senegal, most reports on ATL and HAM/TSP in African patients have been published by European and American clinicians and involve immigrants or medical returnees to Europe (France and the UK) and the United States. There is clearly a huge underreporting of these diseases on the African continent. The genetic diversity of HTLV-1 is greatest in Africa, where six distinct genotypes (a, b, d, e, f, g) have been identified. The most frequent genotype in central Africa is genotype b. The other genotypes found in central Africa (d, e, f and g) are very rare. The vast majority of HTLV-1 strains from West and North Africa belong to genotype a, the so-called 'Cosmopolitan' genotype. These strains form five clades roughly reflecting the geographic origin of the infected individuals. We have recently shown that some of these clades are the result of recombination between a-WA and a-NA strains. Almost all sequences from southern Africa belong to Transcontinental a-genotype subgroup.