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Concept: Human T-lymphotropic virus


Fatality rates of infectious diseases are often higher in men than women. Although this difference is often attributed to a stronger immune response in women, we show that differences in the transmission routes that the sexes provide can result in evolution favouring pathogens with sex-specific virulence. Because women can transmit pathogens during pregnancy, birth or breast-feeding, pathogens adapt, evolving lower virulence in women. This can resolve the long-standing puzzle on progression from Human T-cell Lymphotropic Virus Type 1 (HTLV-1) infection to lethal Adult T-cell Leukaemia (ATL); a progression that is more likely in Japanese men than women, while it is equally likely in Caribbean women and men. We argue that breastfeeding, being more prolonged in Japan than in the Caribbean, may have driven the difference in virulence between the two populations. Our finding signifies the importance of investigating the differences in genetic expression profile of pathogens in males and females.

Concepts: Sex, Infection, Gender, Bacteria, Immune system, Infectious disease, Evolution, Human T-lymphotropic virus


HTLV-1 infection is endemic among people of Melanesian descent in Papua New Guinea, the Solomon Islands and Vanuatu. Molecular studies reveal that these Melanesian strains belong to the highly divergent HTLV-1c subtype. In Australia, HTLV-1 is also endemic among the Indigenous people of central Australia; however, the molecular epidemiology of HTLV-1 infection in this population remains poorly documented.

Concepts: Elizabeth II of the United Kingdom, Pacific Ocean, Human T-lymphotropic virus, Oceania, Melanesia, Solomon Islands, Papua New Guinea, Australia


The Human T Lymphotropic Virus type 1 (HTLV-1) subtype C is endemic to central Australia where each of the major sequelae of HTLV-1 infection has been documented in the socially disadvantaged Indigenous population. Nevertheless, available epidemiological information relating to HTLV-1c infection is very limited, risk factors for transmission are unknown and no coordinated program has been implemented to reduce transmission among Indigenous Australians. Identifying risk factors for HTLV-1 infection is essential to direct strategies that could control HTLV-1 transmission.

Concepts: Western Australia, Central Australia, Virus, Epidemiology, Northern Territory, Human T-lymphotropic virus, Indigenous Australians, Australia


Viruses causing chronic infection artfully manipulate infected cells to enable viral persistence in vivo under the pressure of immunity. Human T-cell leukemia virus type 1 (HTLV-1) establishes persistent infection mainly in CD4+ T cells in vivo and induces leukemia in this subset. HTLV-1-encoded Tax is a critical transactivator of viral replication and a potent oncoprotein, but its significance in pathogenesis remains obscure due to its very low level of expression in vivo. Here, we show that Tax is expressed in a minor fraction of leukemic cells at any given time, and importantly, its expression spontaneously switches between on and off states. Live cell imaging revealed that the average duration of one episode of Tax expression is ∼19 hours. Knockdown of Tax rapidly induced apoptosis in most cells, indicating that Tax is critical for maintaining the population, even if its short-term expression is limited to a small subpopulation. Single-cell analysis and computational simulation suggest that transient Tax expression triggers antiapoptotic machinery, and this effect continues even after Tax expression is diminished; this activation of the antiapoptotic machinery is the critical event for maintaining the population. In addition, Tax is induced by various cytotoxic stresses and also promotes HTLV-1 replication. Thus, it seems that Tax protects infected cells from apoptosis and increases the chance of viral transmission at a critical moment. Keeping the expression of Tax minimal but inducible on demand is, therefore, a fundamental strategy of HTLV-1 to promote persistent infection and leukemogenesis.

Concepts: Natural killer cell, Cytotoxic T cell, Gene expression, Cancer, Immune system, Human T-lymphotropic virus, Virus, Leukemia


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.

Concepts: Malaria, Middle East, Virus, Leukemia, Africa, Human T-lymphotropic virus, Epidemiology, North Africa


The Human T-Lymphotropic Virus type 1c subtype (HTLV-1c) is highly endemic to central Australia where the most frequent complication of HTLV-1 infection in Indigenous Australians is bronchiectasis. We carried out a prospective study to quantify the prognosis of HTLV-1c infection and chronic lung disease and the risk of death according to the HTLV-1c proviral load (pVL).

Concepts: Epidemiology, Disease, Central Australia, Human T-lymphotropic virus, Northern Territory, Indigenous Australians, Virus, Australia



Human T lymphotropic virus type I (HTLV-I)-associated myelopathy/tropical spastic paraparesis (HAM/TSP) is a chronic myelopathy characterized by motor dysfunction of the lower extremities and urinary disturbance. Immunomodulatory treatments are the main strategy for HAM/TSP, but several issues are associated with long-term treatment. We conducted a clinical trial with prosultiamine (which has apoptotic activity against HTLV-I-infected cells) as a novel therapy in HAM/TSP patients.

Concepts:, Clinical trial, Medicine, Effectiveness, Tropical spastic paraparesis, Virus, Human T-lymphotropic virus


Prosultiamine, a vitamin B1 derivative, has long been used for beriberi neuropathy and Wernicke’s encephalopathy. Based on the finding that prosultiamine induces apoptosis in human T lymphotropic virus type-I (HTLV-I)-infected T cells, Nakamura et al conducted a clinical trial of prosultiamine in patients with HTLV-I-associated myelopathy (HAM)/tropical spastic paraparesis (TSP). In this open-label, single arm study enrolling 24 HAM/TSP patients recently published in BMC Medicine, oral prosultiamine (300 mg/day for 12 weeks) was found to be effective by neurological, urological and virological evaluations. Notably, it increased detrusor pressure, bladder capacity and maximum flow rate, and improved detrusor overactivity and detrusor-sphincter dyssynergia. A significant decrease in HTLV-I copy numbers in peripheral blood following the treatment provided a rationale for using the drug. The trial has some limitations, such as the small numbers of participants, the open-label design, the lack of a placebo arm, and the short trial period. Nevertheless, the observation that such a safe, cheap drug may have excellent therapeutic effects on HAM/TSP, a chronic devastating illness occurring mainly in developing countries, provides support for future large-scale randomized controlled trials.Please see related research:

Concepts: Wernicke-Korsakoff syndrome, Vitamin, Beriberi, Virus, Tropical spastic paraparesis, Medicine, Human T-lymphotropic virus, Thiamine


Background Human T-lymphotropic virus type 1 (HTLV-1) causes the debilitating neuroinflammatory disease HTLV-1-associated myelopathy-tropical spastic paraparesis (HAM-TSP) as well as adult T-cell leukemia-lymphoma (ATLL). In patients with HAM-TSP, HTLV-1 infects mainly CCR4+ T cells and induces functional changes, ultimately causing chronic spinal cord inflammation. We evaluated mogamulizumab, a humanized anti-CCR4 monoclonal antibody that targets infected cells, in patients with HAM-TSP. Methods In this uncontrolled, phase 1-2a study, we assessed the safety, pharmacokinetics, and efficacy of mogamulizumab in patients with glucocorticoid-refractory HAM-TSP. In the phase 1 dose-escalation study, 21 patients received a single infusion of mogamulizumab (at doses of 0.003 mg per kilogram of body weight, 0.01 mg per kilogram, 0.03 mg per kilogram, 0.1 mg per kilogram, or 0.3 mg per kilogram) and were observed for 85 days. Of those patients, 19 continued on to the phase 2a study and received infusions, over a period of 24 weeks, of 0.003 mg per kilogram, 0.01 mg per kilogram, or 0.03 mg per kilogram at 8-week intervals or infusions of 0.1 mg per kilogram or 0.3 mg per kilogram at 12-week intervals. Results The side effects of mogamulizumab did not limit administration up to the maximum dose (0.3 mg per kilogram). The most frequent side effects were grade 1 or 2 rash (in 48% of the patients) and lymphopenia and leukopenia (each in 33%). The dose-dependent reduction in the proviral load in peripheral-blood mononuclear cells (decrease by day 15 of 64.9%; 95% confidence interval [CI], 51.7 to 78.1) and inflammatory markers in cerebrospinal fluid (decrease by day 29 of 37.3% [95% CI, 24.8 to 49.8] in the CXCL10 level and of 21.0% [95% CI, 10.7 to 31.4] in the neopterin level) was maintained with additional infusions throughout the phase 2a study. A reduction in spasticity was noted in 79% of the patients and a decrease in motor disability in 32%. Conclusions Mogamulizumab decreased the number of HTLV-1-infected cells and the levels of inflammatory markers. Rash was the chief side effect. The effect of mogamulizumab on clinical HAM-TSP needs to be clarified in future studies. (Funded by the Japan Agency for Medical Research and Development and the Ministry of Health, Labor, and Welfare; UMIN trial number, UMIN000012655 .).

Concepts: Monoclonal antibodies, Spinal cord, Immune system, Cerebrospinal fluid, Inflammation, Virus, Human T-lymphotropic virus, Spinal cord injury