Screening of blood donations for HTLV-I/II

Serological and Molecular Methods to Study Epidemiological Aspects of Human T-Cell Lymphotropic Virus Type 1 Infection

We estimated that at least 5-10 million individuals are infected with HTLV-1. Importantly, this number is based on the study of nearly 1.5 billion people living in known human T-cell lymphotropic virus type 1 (HTLV-1) endemic areas, for which reliable epidemiological data are available. However, for some highly populated regions including India, the Maghreb, East Africa, and some regions of China, no consistent data are yet available which prevents a more accurate estimation. Thus, the number of HTLV-1 infected people in the world is probably much higher. The prevalence of HTLV-1 prevalence varies depending on age, sex, and economic level in most HTLV-1 endemic areas. HTLV-1 seroprevalence gradually increases with age, especially in women. HTLV-1 has a simian origin and was originally acquired by humans through interspecies transmission from STLV-1 infected monkeys in the Old World. Three main modes of HTLV-1 transmission have been described; (1) from mother-to-child after prolonged breast-feeding lasting more than six months, (2) through sexual intercourse, which mainly, but not exclusively, occurs from male to female and lastly, (3) from contaminated blood products, which contain HTLV-1 infected lymphocytes. In specific areas, such as Central Africa, zoonotic transmission from STLV-1 infected monkeys to humans is still ongoing.The diagnostic methods used to study the epidemiological aspects of HTLV-1 infection mainly consist of serological assays for the detection of antibodies specifically directed against different HTLV-1 antigens. Screening tests are usually based on enzyme-linked immunoabsorbent assay (ELISA), chemiluminescence enzyme-linked immunoassay (CLEIA) or particle agglutination (PA). Confirmatory tests include mostly Western blots (WB)s or innogenetics line immunoassay (INNO-LIA™) and to a lesser extent immunofluorescence assay (IFA). The search for integrated provirus in the DNA from peripheral blood cells can be performed by qualitative and/or quantitative polymerase chain reaction (qPCR). qPCR is widely used in most diagnostic laboratories and quantification of proviral DNA is useful for the diagnosis and follow-up of HTLV-1 associated diseases such as adult T-cell leukemia (ATL) and tropical spastic paraparesis/HTLV-1 associated myelopathy (TSP/HAM). PCR also provides amplicons for further sequence analysis to determine the HTLV-1 genotype present in the infected person. The use of new generation sequencing methodologies to molecularly characterize full and/or partial HTLV-1 genomic regions is increasing. HTLV-1 genotyping generates valuable molecular epidemiological data to better understand the evolutionary history of this virus.

Blood safety strategies for human T-cell lymphotropic virus in Europe

BACKGROUND

To prevent the blood transmission of human T-cell lymphotropic virus (HTLV), different countries have introduced anti-HTLV blood screening. Furthermore, leucoreduction of blood components has been implemented to preclude the transmission of infectious agents present in white blood cells.

STUDY DESIGN AND METHODS

To evaluate the current European strategies adopted to ensure the blood safety for HTLV, a European investigation spanning a period from 2003 to 2008 was carried out.

RESULTS

In 2003, of the 23 included countries, 11 performed anti-HTLV screening, four of which (Scandinavian countries) only did it on first-time donors. Norway and Finland stopped it in 2007 and 2008, respectively. Two groups may be defined according to increasing prevalence rates per 10 000 donations in first-time donors: Scandinavia and Ireland (0 to 0.17), France, the Netherlands and UK (0.45 to 0.48); Romania was clearly apart from all other participating countries (5.33). HTLV-positive donors (88.6%) either come from endemic areas (82.3%) or declare to have a sexual partner coming from endemic areas (6.3%). Of the 283 HTLV-positive donations that could be characterized, 6.6% were HTLV-II. Fourteen of 22 countries currently use systematic leucoreduction, at least in cellular blood components. Six countries perform both universal anti-HTLV screening and blood cell leucoreduction.

CONCLUSION

The implementation of leucoreduction did not modify the blood HTLVscreening policy, except for Norway and Finland. Several screening strategies in low endemic countries performing leucoreduction were discussed. However, the withdrawal of anti-HTLV screening should be decided after assessing the remaining HTLV transfusion risk.

Trends in residual risk of transfusion-transmitted viral infections in France between 1992 and 2000

BACKGROUND

Monitoring trends in residual risks of transfusion-transmitted viral infections (HIV, HTLV, HBV, and HCV) is important to assess improvements in blood safety. In France, theses trends were analyzed between 1992 and 2000.

STUDY DESIGN AND METHODS

As risk is predominantly associated with the window period, residual risks were estimated by multiplying incidence rates by the durations of the window periods. Incidence rates were calculated from the data collected by the blood transfusion centers belonging to the Transfusion-Transmissible Agents Working Group, which currently collects more than 50 percent of the 2.5 million blood samples donated each year in France.

RESULTS

Trend analysis showed a significant decrease in residual risks for HCV (p = 0.01) and HBV (p < 0.001). Although residual risks decreased for HIV and HTLV, the trends were not significant. In 1998 through 2000, residual risks were estimated to be 1 in 470,000 donations for HBV, 1 in 860,000 for HCV, 1 in 1,370,000 for HIV, nil for HTLV, and 1 in 250,000 for the four viruses combined.

CONCLUSIONS

In France, the current risk of a blood recipient becoming infected with a retrovirus or a hepatitis virus is extremely low. The implementation of NAT in July 2001 is predicted to reduce the residual risk to 1 in 2,700,000 donations for HIV and 1 in 8,300,000 for HCV.

Quality control of leucoreduced cellular blood components in France

BACKGROUND AND OBJECTIVES

Since 1 April 1998, all cellular blood components in France have been leucoreduced. The current French standard is < 1 x 10(6) white blood cells (WBC) per unit with a 95% confidence that at least 97% of units will meet this standard.

MATERIALS AND METHODS

Quality control (QC) data for leucoreduced cellular blood components were collected from the 41 French blood centres over a 5-month period. Conformance to the standard was determined using a non-parametric approach.

RESULTS

More than 98% of the 15 286 red cell concentrates and of the 2895 platelet concentrates tested had < 1 x 10(6) WBC per unit. One filtration device gave unsatisfactory results and its use was discontinued.

CONCLUSION

This QC survey shows an overall compliance with the standard. The data illustrate the practical value of identifying devices or centres with consistent QC problems.

Leucocyte depletion of blood components

Universal leucocyte depletion has been implemented in the UK and several other European countries as a precautionary measure against the potential risk of transmission of variant Creutzfeldt-Jakob disease by blood transfusion. Leucocyte depletion had previously only been recommended for a relatively small proportion of transfusion recipients based on clinical and experimental evidence showing clinical benefit. However there is now increasing evidence to support its value in preventing transfusion transmission of infectious agents and in reducing some of the adverse immunomodulatory effects of allogeneic transfusion. The financial costs of providing universal leucocyte depletion are substantial, but, if it transpires that leucocyte depletion has a beneficial effect in reducing, for example, postoperative infection rates, then the health economic gains in this patient group alone may largely or wholly offset these financial costs. The experience in the UK and other European countries in terms of these collateral clinical benefits will help other countries, where the risk of variant Creutzfeldt-Jakob disease may not be so great, to decide whether to similarly adopt universal leucocyte depletion.