The epidemiology of human T-cell lymphotropic virus types I and II in Canadian blood donors

Prevalence of human T-cell lymphotropic virus-1/2 in Canada over 33 years: A unique contribution of blood donors to public health surveillance

OBJECTIVES

Estimate HTLV-1/2 (human T-cell lymphotropic viruses) prevalence in Canadian blood donors and the association of demographic variables with infection and their corresponding risk factors.

METHODS

First-time blood donors in all Canadian provinces (except Quebec) from 1990 to 2022 were included. Blood samples were tested for HTLV-1/2 by enzyme-linked immunoassay, confirmed by Western blot. Multivariable logistic regression with year, age group, sex, region, neighbourhood material deprivation, and ethnocultural composition indices predicted HTLV-1/2. Since 2005, all HTLV-1/2-positive donors (cases) were invited to participate in a risk factor interview, and 4 non-positive donors (controls per case) were matched for age, sex, and region. Case-control predictors of HTLV-1/2 were analyzed using logistic regression.

RESULTS

There were 3,085,554 first-time donors from 1990 to 2022. HTLV-1/2 prevalence remained low (12 per 100,000 in 2022, 95% CI 6.4-23.5). The odds ratios predicting HTLV-1/2 were higher in females (2.0, 95% CI 1.5-2.6), older age groups (50 + ; 6.3, 95% CI 4.3-9.2), British Columbia and Ontario, those materially deprived (1.9, 95% CI 1.2-2.9), and those in ethnocultural neighbourhoods (7.5, 95% CI 3.2-17.3). Most HTLV-1/2 in Ontario was HTLV-1, whereas in British Columbia half were HTLV-2. Forty-three of 149 (28.8%) cases and 172 of 413 (41.6%) controls completed an interview. The strongest predictor of HTLV-1/2 in case-control analysis was birth in a high-prevalence country (OR 39.8, 95% CI 7.8-204.3) but about 50% of HTLV-1 and 90% of HTLV-2 were Canadian-born.

CONCLUSION

HTLV-1/2 prevalence is low in blood donors. High-prevalence country of birth accounts for about half of HTLV-1; HTLV-2 positives are usually Canadian-born. HTLV-1/2 transmission likely occurs overseas and within Canada.

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.

Improvement of the understanding of blood donors with human T-cell leukaemia virus type 1 using a new information booklet

Background

Human T‐cell leukaemia virus type 1 (HTLV‐1) tests have been mandated in Japan since 1986, and notification of HTLV‐1‐seropositive donors started in 1999. However, donor knowledge and response to notification has not been assessed.

Study design and Methods

A questionnaire survey was conducted among blood donors notified of HTLV‐1 seropositivity regarding their knowledge of HTLV‐1 and unmet information needs. To reduce anxiety among notified individuals and raise awareness of their infection status, we created a booklet containing information that would be useful for these individuals without causing unnecessary anxiety while also requesting that they refrain from donating blood in the future.

Results

A questionnaire survey conducted before the distribution of a new booklet revealed that 15.0% of respondents donated blood again despite receiving an HTLV‐1‐seropositive notification at the previous donation. While 62.2% of respondents reacted to the notification favourably, 40.2% expressed anxiety and 32.5% requested information on related diseases and medical institutions for consultation. In the secondary survey after distribution of the new booklet, 87.9% of respondents reported that the information was comprehensible, and an increase in consultations of medical institutions by notification recipients was observed. Furthermore, no re‐visiting donors were observed among the HTLV‐1‐seropositive recipients who were notified using the new information booklet.

Conclusion

The new information booklet provided enlightenment on HTLV‐1 infection and facilitated the consultation of medical institutions by seropositive donors, leading to an improvement in the health‐related quality of life of seropositive blood donors and the safety of blood products.

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.

Comparative virology of HTLV-1 and HTLV-2

Human T cell leukemia virus type 1 (HTLV-1) was the first discovered human retrovirus and the etiologic agent of adult T-cell leukemia and HTLV-1-associated myelopathy/tropical spastic paraparesis. Shortly after the discovery of HTLV-1, human T-cell leukemia virus type 2 (HTLV-2) was isolated from a patient with hairy cell leukemia. Despite possession of similar structural features to HTLV-1, HTLV-2 has not been definitively associated with lymphoproliferative disease. Since their discovery, studies have been performed with the goal of highlighting the differences between HTLV-1 and HTLV-2. A better understanding of these differences will shed light on the specific pathogenic mechanisms of HTLV-1 and lead to novel therapeutic targets. This review will compare and contrast the two oldest human retroviruses with regards to epidemiology, genomic structure, gene products, and pathobiology.

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.

Prevalence of human T cell lymphotropic virus 1 infection in Canada

Human T cell lymphotropic virus 1 (htlv-1) is a bloodborne retrovirus that infects at least 5–20 million people around the world [...]

Prevalence and risk factors for Human T-Lymphotropic Virus Type 1 (HTLV-1) among maintenance hemodialysis patients

Background

Infection with the human T-cell lymphotropic virus type 1 (HTLV-1), although asymptomatic in most cases, can lead to potentially grave consequences, such as adult T-cell leukemia-lymphoma and HTLV-1-associated myelopathy / tropical spastic paraparesis. Its prevalence varies widely across different populations and geographic regions. A population-based study in the city of Salvador, located in the Northeast region of Brazil, showed an overall prevalence of HTLV-1 seropositivity of 1.7%. Blood borne virus infections are recognized as important hazards for patients and staff in maintenance hemodialysis (MHD) units but most studies focus on hepatitis B, hepatitis C and human immunodeficiency viruses. There are scarce data about HTLV-1 infection in the MHD population. We aimed to determine the prevalence and risk factors for HTLV-1 infection among MHD patients in the city of Salvador-Bahia, Brazil.

Methods

We conducted a multi-center, cross-sectional study nested in a prospective cohort of MHD patients enrolled from four outpatient clinics. HTLV-1 screening was performed with ELISA and positive cases were confirmed by Western Blot. Factors associated with HTLV-1 seropositivity were identified by multivariable logistic regression.

Results

605 patients were included in the study. The overall prevalence of HTLV-1 infection was 2.48% (15/605), which was similar to that of hepatitis B [1.98% (12/605)] and C [3.14% (19/605)] viruses in our sample. HTLV-1 seropositivity was positively associated with age [prevalence odds ratio (POR) 1.04; 95% confidence interval (CI) 1.01–1.08], unmarried status (POR 3.65; 95% CI 1.13–11.65), and history of blood transfusion (POR 3.35; 95% CI 1.01–11.13).

Conclusions

The overall prevalence of HTLV-1 infection in a sample of MHD patients was similar to that of other viral infections, such as hepatitis B and C. Our data revealed that MHD patients who are older, unmarried or who have received blood transfusions are at higher risk for HTLV-1 infection.

Infection with human T-lymphotropic virus types-1 and -2 (HTLV-1 and -2): Implications for blood transfusion safety

Many countries currently perform antibody screening for HTLV-1 infection in blood donors, and this intervention is likely cost-effective in preventing HTLV-1 related diseases in high prevalence countries. However, a number of high-income countries with low prevalence of HTLV-1 infection also perform universal HTLV-1 screening and debate has arisen regarding the cost-effectiveness of these strategies. Filter-based leukoreduction is likely to substantially reduce HTLV-1 transmission by removing infected lymphocytes, but actual laboratory data on its efficacy is currently lacking. Similarly, cost-effectiveness research on HTLV-1 prevention strategies is limited by poor data on prevalence, transmission efficacy and the cost of treating HTLV1 diseases.

Human T-Lymphotropic Virus Type I (HTLV-1) Infection among Iranian Blood Donors: First Case-Control Study on the Risk Factors

Human T-cell lymphotropic virus type 1 (HTLV-1) infection is an endemic condition in Northeast Iran and, as such, identification of risk factors associated with the infection in this region seems to be a necessity. All the possible risk factors for HTLV-1 seropositivity among first-time blood donors were evaluated in Mashhad, Iran, during the period of 2011–2012. Blood donation volunteers were interviewed for demographic data, medical history, and behavioral characteristics and the frequencies of risk factors were compared between HTLV-1 positive (case) and HTLV-1 negative (control) donors. The data was analyzed using Chi square and t-tests. Logistic regression analysis was performed to identify independent risk factors for the infection. Assessments were carried out on 246 cases aged 17–60 and 776 controls aged 17–59, who were matched based on their ages, gender, and date and center of donation. Logistic analysis showed low income (OR = 1.53, p = 0.035), low educational level (OR = 1.64, p = 0.049), being born in the cities of either Mashhad (OR = 2.47, p = 0.001) or Neyshabour (OR = 4.30, p < 0001), and a history of blood transfusion (OR = 3.17, p = 0.007) or non-IV drug abuse (OR = 3.77, p < 0.0001) were significant predictors for infection with HTLV-1. Lack of variability or small sample size could be reasons of failure to detect some well-known risk factors for HTLV-1 infection, such as prolonged breastfeeding and sexual promiscuity. Pre-donation screening of possible risk factors for transfusion-transmissible infections should also be considered as an important issue, however, a revision of the screening criteria such as a history of transfusion for more than one year prior to donation is strongly recommended.