The prevalence of human T-lymphotropic virus type 1 & 2 (HTLV-1/2) in South African blood donors

HTLV-1 associated myelopathy/tropical spastic paraparesis (HAM/TSP): Case based discussion of risk factors, clinical, and therapeutic considerations

HTLV-1 is a retrovirus virus that infects CD4+ T cells. Most people with HTLV-1 infection remain asymptomatic but some may develop conditions such as HTLV-1 associated myelopathy/tropical spastic paraparesis (HAM/TSP) or adult T-cell leukemia/lymphoma. HAM/TSP is characterized by progressive spasticity and weakness of the lower extremities, as well as loss of bladder control and sensory disturbances. The risk of developing HAM/TSP is associated with the duration of infection and the proviral load. There is currently no cure for the disease but medications can help manage symptoms and slow the progression of the disease. This is the case of a 66-year-old female who presented with nonspecific symptoms of weakness and spasticity in a hospital in Connecticut and was subsequently diagnosed with HAM/TSP. The patient's diagnosis highlights the importance of considering diseases previously confined to specific endemic regions in a globalized world where increased emigration and population mixing can occur. Early identification and management of such cases is essential for optimizing patient outcomes and quality of life.

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.

Low risk of human T-lymphotropic virus infection in U.S. blood donors; Is it time to consider a one-time selective testing approach?

BACKGROUND

U.S. blood donors are tested at each donation for human T-lymphotropic virus (HTLV) antibodies. Depending on donor incidence and other mitigation/removal technologies, a strategy of one-time selective donor testing should be considered.

METHODS

Antibody seroprevalence was calculated for HTLV-confirmed-positive American Red Cross allogeneic blood donors from 2008 to 2021. Incidence was estimated for seven 2-year time periods using confirmed-positive repeat donors having seroconverted in 730 days. Leukoreduction failure rates were obtained from internal data from July 1, 2008-June 30, 2021. Residual risks were calculated using a 51-day window period.

RESULTS

Between 2008 and 2021, >75 million donations (>18 million donors) yielded 1550 HTLV seropositives. HTLV seroprevalence was 2.05 antibody-positives per 100,000 donations (0.77 HTLV-1, 1.03 HTLV-2, 0.24 HTLV-1/2), and 10.32 per 100,000 among >13.9 million first-time donors. Seroprevalence differed significantly by virus type, sex, age, race/ethnicity, donor status, and U.S. census region. Over 14 years and 24.8 million person-years of observation, 57 incident donors were identified (25 HTLV-1, 23 HTLV-2, and 9 HTLV-1/2). Incidence decreased from 0.30 (13 cases) in 2008-2009 to 0.25 (7 cases) in 2020-2021. Female donors accounted for most incident cases (47 vs. 10 males). In the last 2-year reporting period, the residual risk was 1 per 2.8 million donations and 1 per 3.3 billion donations when coupled with successful leukoreduction (0.085% failure rate).

CONCLUSIONS

HTLV donation seroprevalence for the years 2008-2021 varied by virus type and donor characteristics. Low HTLV residual risk and use of leukoreduction processes support the conclusion that a selective one-time donor testing strategy should be considered.

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.

Epidemiology of Adult T-Cell Leukaemia/Lymphoma in South Africa over a 10-Year Period

Introduction

Adult T-cell leukaemia/lymphoma (ATLL) is a rare and aggressive malignancy of mature T-cells. Limited epidemiological studies have shown that there is substantial variation in age at diagnosis and subtype distribution between different geographical regions. This is the first epidemiological study of ATLL in South Africa.

Methods

A national epidemiological study of ATLL in South Africa was performed. All new cases of ATLL from 2009 to 2019 were identified by laboratory database search in public and private health care sectors. Demographic and diagnostic data were obtained, and the cases were subtyped according to the Shimoyama classification.

Results

There were 31 patients with ATLL over the 10-year period, with an incidence of 0.06 per 100000 population. The male to female ratio was 1 : 1 and the median age at diagnosis was 37 years. Acute ATLL was the most commonly seen subtype in South Africa.

Conclusion

In this, the first epidemiological study of ATLL in South Africa, we demonstrate that ATLL is a rare disease, that acute ATLL is the most commonly diagnosed subtype, and that ATLL is likely under diagnosed. Patients present at a considerably younger age than the reported age in other nations.

Epidemiological evidence of nosocomial and zoonotic transmission of HTLV-1 in a large survey in rural population of central Africa

BACKGROUND

Central Africa is one of the largest areas of high endemicity for human T-cell leukaemia virus (HTLV-1). However, no preventive measures are yet implemented to reduce its transmission, which can be sexual, from mother-to-child, or through contaminated blood products. Rare zoonotic transmissions from non-human primates (NHPs) have also been reported in this region. Here, we investigated the HTLV-1 prevalence and associated risk factors in a rural population in Cameroon.

METHODS

From 2019 to 2021, we performed a cross-sectional survey in the Eastern region of Cameroon. HTLV-1 infection was first screened by ELISA, then tested by Western blot and envelope gene targeted polymerase chain reaction. Risk factors associated with HTLV-1 infection were identified by logistic regression on univariable and multivariable analyses.

RESULTS

Among 3,400 participants, HTLV-1 prevalence was 1.1% (95%CI 0.7-1.5). Factors independently associated with HTLV-1 infection were: Pygmy ethnicity (adjusted odd ratio ORa, 2.9, 95%CI 1.3-6.2), history of surgery (ORa 6.3, 95%CI 2.2-17.8) and NHP bite (ORa 6.6, 95%CI 2.2-19.8).

CONCLUSIONS

These results suggest both iatrogenic and zoonotic transmission of HTLV-1 in Cameroon. Further studies are needed to assess the risk of nosocomial transmission of HTLV-1, to guide public health authorities in implementing preventive measures to control HTLV-1 transmission.

Human T-Lymphotropic virus type 1 and human immunodeficiency virus co-infection in rural Gabon

Introduction

Human T-cell lymphotrophic virus type-1 (HTLV-1) and human immunodeficiency virus (HIV-1) co-infection occur in many populations. People living with HIV-1 and infected with HTLV-1 seem more likely to progress rapidly towards AIDS. Both HTLV-1 and HIV-1 are endemic in Gabon (Central Africa). We investigated HTLV-1 and HIV-1 co-infection in the Haut-Ogooué province, and assessed factors that may favor the rapid evolution and progression to AIDS in co-infected patients.

Methods

Plasma samples from HTLV-1 patients were tested using ELISA, and positive samples were then tested by western blot assay (WB). We used the polymerase chain reaction to detect HTLV-1 Tax/Rex genes using DNA extracted from the buffy coat of ELISA-positives samples.

Results

We recruited 299 individuals (mean age 46 years) including 90 (30%) men and 209 (70%) women, all of whom are under treatment at the Ambulatory Treatment Centre of the province. Of these, 45 were ELISA HTLV-1/2 seropositive. According to WB criteria, 21 of 45 were confirmed positive: 20 were HTLV-1 (44%), 1 was HTLV-1/2 (2%), 2 were indeterminate (4%) and 22 were seronegative (49%). PCR results showed that 23 individuals were positive for the Tax/Rex region. Considering both serological and molecular assays, the prevalence of HTLV-1 infection was estimated at 7.7%. Being a woman and increasing age were found to be independent risk factors for co-infection. Mean CD4+ cell counts were higher in HTLV-1/HIV-1 co-infected (578.1 (± 340.8) cells/mm³) than in HIV-1 mono-infected (481.0 (± 299.0) cells/mm³) Individuals. Similarly, the mean HIV-1 viral load was Log 3.0 (± 1.6) copies/ml in mono-infected and Log 2.3 (± 0.7) copies/ml in coinfected individuals.

Conclusion

We described an overall high prevalence of HTLV-1/HIV-1 co-infection in Gabon. Our findings stress the need of strategies to prevent and manage these co-infections.

Clinical and Public Health Implications of Human T-Lymphotropic Virus Type 1 Infection

Human T-lymphotropic virus type 1 (HTLV-1) is estimated to affect 5 to 10 million people globally and can cause severe and potentially fatal disease, including adult T-cell leukemia/lymphoma (ATL) and HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). The burden of HTLV-1 infection appears to be geographically concentrated, with high prevalence in discrete regions and populations. While most high-income countries have introduced HTLV-1 screening of blood donations, few other public health measures have been implemented to prevent infection or its consequences. Recent advocacy from concerned researchers, clinicians, and community members has emphasized the potential for improved prevention and management of HTLV-1 infection. Despite all that has been learned in the 4 decades following the discovery of HTLV-1, gaps in knowledge across clinical and public health aspects persist, impeding optimal control and prevention, as well as the development of policies and guidelines. Awareness of HTLV-1 among health care providers, communities, and affected individuals remains limited, even in countries of endemicity. This review provides a comprehensive overview on HTLV-1 epidemiology and on clinical and public health and highlights key areas for further research and collaboration to advance the health of people with and at risk of HTLV-1 infection.

Strengths, Weaknesses, Opportunities and Threats (SWOT) Analysis of the Implementation of Public Health Policies on HTLV-1 in Brazil

Human T lymphotropic virus 1 (HTLV-1) is a public health issue for most countries and imposes important consequences on patients' health and socioeconomic status. Brazil is one of the global leaders of the public health response to these viruses. The country has challenges to overcome to implement meaningful policies aiming to eliminate HTLV-1/2. An analysis of strengths, weaknesses, opportunities, and threats (SWOT) for the implementation of public health policies on HTLV-1/2 was performed. The strengths identified were the Brazilian Unified Health System (SUS); Brazilian expertise in public health programs successfully implemented; currently available policies targeting HTLV; and strong collaboration with researchers and patient's representative. Lack of awareness about HTLV, insufficient epidemiological data, lack of reference centers for patient care, insufficient availability of confirmatory tests, lack of universal antenatal screening, and absence of cost-effectiveness studies were identified as weaknesses. Some interesting opportunities included the increased interest from international organizations on HTLV, possibility of integrating HTLV into other programs, external funding for research, available online platforms, opportunity to acquire data from HTLV-1/2 surveillance to gather epidemiological information, and HTLV policies that were implemented independently by states and municipalities. In addition to the COVID-19 pandemic, existing demands from different diseases, the country's demography and its marked sociocultural diversity and the volatility of the technical team working with HTLV-1/2 at the Brazilian Ministry of Health are threats to the implementation of public policies on HTLV-1/2. This SWOT analysis will facilitate strategic planning to allow continuous progress of the Brazilian response to HTLV-1/2 infection.

Human T-cell leukemia virus type 1 infection among Japanese immigrants and their descendants living in Southeast Brazil: A call for preventive and control responses

Human T-cell leukemia virus type 1 (HTLV-1) has worldwide distribution and is considered endemic in southwestern Japan. HTLV-1 infection has been associated with adult T-cell leukemia/lymphoma (ATL) and HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) besides other diseases. This cross-sectional study aimed to investigate the prevalence, risk factors and molecular characterization of HTLV-1, among the world’s largest population of Japanese immigrants and their descendants outside of Japan, in São Paulo, Southeast Brazil, as well as to analyze the phylogenetic relationship among isolates of HTLV-1. From July to December 2017, 2,139 individuals from five Japanese associations were interviewed and submitted to blood collection. All serum samples were first tested for the presence of anti-HTLV-1/2 antibodies by ELISA and then peripheral blood from individuals with positive serological results were analyzed for the presence of HTLV-1 5’LTR proviral DNA. Partial sequencing of the 5’LTR region of HTLV-1 proviral DNA was performed by Sanger. The prevalence of HTLV-1 infection was 5.1% (CI 95%: 4.2–6.0). In the multiple logistic regression model, HTLV-1 infection was associated with age ≥ 45 years, female sex, being first and second-generation Japanese immigrants, and having sexual partners with history of blood transfusion. The phylogenetic analysis revealed that all HTLV-1 were classified as Cosmopolitan (1a) subtype. Of them, 47.8% were classified as Transcontinental (A) subgroup and 52.2% as belonging to the Japanese (B) subgroup. Although most HTLV-1-infected patients were asymptomatic (97.3%), blurred vision was associated with HTLV-1 infection. The high prevalence of HTLV-1 infection found in this studied population and especially the intra- and interfamily HTLV-1 transmission presents an urgent call for preventive and control responses of this infection in Brazil.

What is the prevalence of HTLV-1 among the largest world population of Japanese immigrants and their descendants outside Japan? There are approximately 1.5 million people of Japanese descent in Brazil and most of them living in São Paulo state, Southeast Brazil. The prevalence of HTLV-1 infection was 5.1% among 2,139 individuals from five Japanese associations in São Paulo. The prevalence of 5.1% (95% CI: 4.2–6.0) of HTLV-1 infection found in this study is higher than those observed in other studies conducted in HTLV-1 endemic areas and in specific groups at high risk from Brazil. Among HTLV-infected individuals, the majority (86.2%) were unaware of their HTLV diagnosis. The HTLV-1 infection was associated with the age ≥ 45 years, being the first and second generation of Japanese immigrants, and having sexual partners with a history of blood transfusion. Epidemiological data, along with molecular results also demonstrated high occurrence of similar sequences transmitted intra- and interfamily. The high prevalence of HTLV-1 infection found in this studied population presents an urgent call for preventive and control responses of this infection in Brazil.

Multiple recombinant events in human T-cell Leukemia virus Type 1: complete sequences of recombinant African strains

Africa is the largest endemic area for HTLV-1, with many molecular genotypes. We previously demonstrated that some strains from North Africa (a-NA clade) originated from a recombinant event between Senegalese and West African strains. A series of 52 new HTLV-1 strains from 13 North and West African countries were sequenced in the LTR region and/or a env gene fragment. Four samples from French Guyanese of African origin were also added. Furthermore, 7 complete sequences from different genotypes were characterized. Phylogenetic analyses showed that most of the new African strains belong to the Cosmopolitan a-genotype. Ten new strains from the a-NA clade were found in Morocco, Western Sahara, Mali, Guinea, Côte d'Ivoire and Ghana. A new a-G-Rec clade, which arose from a distinct recombination event between Senegalese and West African strains, was identified in Guinea and Ghana. The complete sequences suggest that recombination occur in the LTR as well as the env/pol region of the genome, thus a-NA and a-G-Rec strains have a mosaic profile with genetic segments from either a-WA or a-Sen strains. Our work demonstrates that recombination in HTLV-1 may not be as rare an event as previously proposed.

High prevalence of human T-cell leukemia virus type-1b genotype among blood donors in Gabon, Central Africa

BACKGROUND

The African continent is considered to be the largest endemic area of HTLV‐1 infection, with at least several million infected individuals. Systematic screening of blood donors can prevent the transmission of HTLV‐1 in blood. Gabon is one of the countries with the highest prevalence of HTLV‐1 worldwide, and yet the routine testing of blood donors has still not been introduced.

METHODS

All blood donations collected between April and July 2017 at the Centre National de Transfusion Sanguine of Gabon were studied. Plasma samples were screened by ELISA for the presence of HTLV‐1/2 antibodies. Western blot (WB) and polymerase chain reaction (PCR) tests were used for confirmation.

RESULTS

In total, 3123 blood donors were tested, including 1740 repeat and 1378 first‐time blood donors (FTBDs). Of them, 132 samples tested positive for HTLV‐1/2 by ELISA (4.2%). WB and PCR confirmed HTLV‐1 infection for 23 individuals. The overall prevalence of HTLV‐1 was 0.74% [95% CI 0.47%‐1.10%], 1% in FTBD, and 0.5% in repeat donors. Age and sex‐adjusted prevalence was five‐fold lower in FTBD than in the general adult population of rural areas of Gabon. All detected HTLV‐1 strains belonged to the central African HTLV‐1b genotype but were highly diverse.

CONCLUSION

We report an overall prevalence of HTLV‐1 of 0.74%, one of the highest values reported for blood donors in Africa. Given the high risk of HTLV‐1 transmission in blood, it is necessary to conduct cost‐effectiveness studies to determine the need and feasibility of implementing screening of HTLV‐1 in blood donors in Gabon.

Molecular epidemiology, genetic variability and evolution of HTLV-1 with special emphasis on African genotypes

Human T cell leukemia virus (HTLV-1) is an oncoretrovirus that infects at least 10 million people worldwide. HTLV-1 exhibits a remarkable genetic stability, however, viral strains have been classified in several genotypes and subgroups, which often mirror the geographic origin of the viral strain. The Cosmopolitan genotype HTLV-1a, can be subdivided into geographically related subgroups, e.g. Transcontinental (a-TC), Japanese (a-Jpn), West-African (a-WA), North-African (a-NA), and Senegalese (a-Sen). Within each subgroup, the genetic diversity is low. Genotype HTLV-1b is found in Central Africa; it is the major genotype in Gabon, Cameroon and Democratic Republic of Congo. While strains from the HTLV-1d genotype represent only a few percent of the strains present in Central African countries, genotypes -e, -f, and -g have been only reported sporadically in particular in Cameroon Gabon, and Central African Republic. HTLV-1c genotype, which is found exclusively in Australo-Melanesia, is the most divergent genotype. This reflects an ancient speciation, with a long period of isolation of the infected populations in the different islands of this region (Australia, Papua New Guinea, Solomon Islands and Vanuatu archipelago). Until now, no viral genotype or subgroup is associated with a specific HTLV-1-associated disease. HTLV-1 originates from a simian reservoir (STLV-1); it derives from interspecies zoonotic transmission from non-human primates to humans (ancient or recent). In this review, we describe the genetic diversity of HTLV-1, and analyze the molecular mechanisms that are at play in HTLV-1 evolution. Similar to other retroviruses, HTLV-1 evolves either through accumulation of point mutations or recombination. Molecular studies point to a fairly low evolution rate of HTLV-1 (between 5.6E−7 and 1.5E−6 substitutions/site/year), supposedly because the virus persists within the host via clonal expansion (instead of new infectious cycles that use reverse transcriptase).

Health economic implications of testing blood donors in South Africa for HTLV 1 & 2 infection

BACKGROUND AND OBJECTIVES

Currently, HTLV screening is not performed in South Africa (SA). This report describes an economic assessment (budget impact and cost-effectiveness) of implementing different HTLV screening strategies.

METHODS

A modified version of the Alliance of Blood Operators risk-based decision-making framework was used to assess the risk and consequences of HTLV in the blood supply in SA. We developed a deterministic model of the cost and consequences of four screening strategies: none, universal, all donors once and first time donors only assuming a transfusion-transmission (TT) efficiency of 10% and a manifestation of clinical disease of 6%.

RESULTS

Unscreened blood results in 3·55 symptomatic TT-HTLV cases and a total healthcare cost of Rand (R)3 446 950 (US Dollars (USD)229 800) annually. Universal screening would cost R24 000 000 (USD1 600 000) per annum and prevent 3·54 (99·8%) symptomatic TT-HTLV cases in the first year and 0·55 (98·4%) symptomatic TT-HTLV cases in the second year at a cost per TT-HTLV prevented of R6 780 000 (USD450 000) in year one and R43 254 000 (USD2 890 000) in year two. Screening all donors once would cost R16,200,000 (USD1 080 000) or R4 600 000 (USD306 000) per symptomatic TT-HTLV infection prevented in year one. Total costs decrease to R5 100 000 (USD340 000) in year 2 but the cost per TT-HTLV prevented increases to R10 700 000 (USD713 333).

CONCLUSION

This analysis contributed to the decision not to implement HTLV screening as the healthcare budget and particularly the budget for blood transfusion in SA is insufficient to provide appropriate treatment. Arguably, available resources can be more efficiently utilized in other healthcare programs.