Detection of human T-lymphotropic virus (HTLV) tax sequences in New York City blood donors seronegative for HTLV types 1 and 2

A potential public health concern is the reported detection of the human T-lymphotropic virus (HTLV) tax gene in the lymphocytes of up to 11% of a low-risk group of New York City blood donors (NYBD). This study aimed to independently confirm the prevalence of HTLV tax sequences in 293 NYBD. All NYBD tested negative for antibodies to HTLV types 1 and 2 and HTLV Tax. HTLV tax sequences were not detected in the NYBD lymphocytes. These data demonstrate the lack of HTLV-1 tax in this group of NYBD at low risk for HTLV infection.     

Human T-Cell Lymphotropic Virus Type 1 Tax among American Blood Donors

In the United States, all blood used for transfusion is tested for the presence of antibodies to the structural components of the human T-cell lymphotropic viruses types 1 and 2 (HTLV-1 and -2). Based on such serologic tests, the prevalence of HTLV-1 infection is estimated to range from 0.016 to 0.1%. As a consequence of studies of patients with mycosis fungoides and some of their healthy relatives who are antibody negative but were found to carry the tax sequence of HTLV-1 in their lymphocytes and who had antibodies to the p40^tax protein, a study was undertaken to determine the prevalence of the “tax-only” state in 250 healthy blood donors and other volunteers. Using PCR and Southern analysis for cell lysates and using Western blotting for plasmas, 8.6% of the blood donors proved to be tax sequence positive and antibody positive. Sequence analysis of specimens from 22 individuals proved that 20 of the sequences were homologous with that of HTLV-1 while 2 resembled the HTLV-2 sequence. The latter were obtained from volunteers of Indian origin. The possible clinical significance of the tax-only carrier state is discussed.     

Transmission of Human T-Cell Lymphotropic Virus Type 1 Tax to Rabbits by tax-Only-Positive Human Cells

The human T-cell lymphrotropic virus type 1 (HTLV-1) is causally related to adult T-cell leukemia and lymphoma and the neurodegenerative diseases tropical spastic paraparesis and HTLV-1-associated myelopathy. In the United States the prevalence of infection has been estimated to range from 0.016 to 0.1% on the basis of serologic tests for antibodies to the viral structural proteins. Blood from donors positive for antibodies to HTLV-1 or HTLV-2 is not used for transfusion. However, patients with the cutaneous T-cell lymphoma mycosis fungoides (MF) are HTLV-1 and -2 seronegative yet harbor proviral sequences identical to those that encode the HTLV-1 transactivating and transforming gene product p40tax in their peripheral blood mononuclear cells (PBMCs), and they usually have antibodies to p40^tax. Moreover, a study of 250 randomly selected blood donors revealed that approximately 8% of these seronegative individuals also had HTLV-1 tax sequences and antibodies to p40^tax, while they lacked sequences and antibodies related to gag, pol, or env. Thus, it seemed important to determine whether the “tax-only” state can be transmitted by transfusion. To this end, PBMCs from HTLV-1 and -2 seronegative tax-only-positive MF patients or from healthy tax-only-positive blood donors were injected into adult rabbits, an established animal model for HTLV-1 infection. The PBMCs of all injected rabbits became tax sequence positive. These observations suggest that HTLV-1 tax can be transmitted by tax-only-positive mononuclear cells.     

Correlation of HTLV‐1 Tax genetic diversity with HTLV‐1 associated myelopathy/tropical spastic paraparesis progression and HTLV‐1a genotypes in an HTLV‐1 endemic region in Argentina

The oncoprotein Tax was characterized genetically from a large cohort of human T‐cell lymphotropic virus type 1 (HTLV‐1) seropositive individuals from the most endemic region of HTLV‐1‐associated myelopathy/tropical spastic paraparesis (HAM/TSP) and HTLV‐1 infection in Argentina, the province of San Salvador de Jujuy. Sixteen HAM/TSP patients and 47 HTLV‐1 healthy carriers were evaluated. Six Tax genetic polymorphisms were identified and observed in 70.8% of healthy carriers and 62.5% of HAM/TSP patients. Tax genetic polymorphisms were not associated with clinical status but A8344C polymorphism statistically provide a borderline protective effect of HAM/TSP outcome. Nucleotide diversity in healthy carriers was 0.00549, whereas HAM/TSP virus population revealed a low diversity of 0.00379, suggests a positive selection for Tax protein conservation in this group. It is concluded that tax genetic polymorphisms do not increase the risk of developing HAM/TSP in this endemic region. However, in spite of the low prevalence of HTLV‐1aB genotype, statistical analysis revealed an important correlation of tax genetic signatures with HTLV‐1aA trans‐continental subgroup. J. Med. Virol. 82:1438–1441, 2010. © 2010 Wiley‐Liss, Inc.     

Emergence of a novel and highly divergent HTLV-3 in a primate hunter in Cameroon

The recent discovery of human T-lymphotropic virus type 3 (HTLV-3) in Cameroon highlights the importance of expanded surveillance to better understand the prevalence and public health impact of this new retrovirus. HTLV diversity was investigated in 408 persons in rural Cameroon who reported simian exposures. Plasma from 29 persons (7.2%) had reactive serology. HTLV tax sequences were detected in 3 persons. Phylogenetic analysis confirmed HTLV-1 infection in two individuals and HTLV-3 infection in a third person (Cam2013AB). The complete proviral genome from Cam2013AB shared 98% identity and clustered tightly in distinct lineage with simian T-lymphotropic virus type 3 (STLV-3) subtype D recently identified in two guenon monkeys near this person's village. These results document a fourth HTLV-3 infection with a new and highly divergent strain we designate HTLV-3 (Cam2013AB) subtype D demonstrating the existence of a broad HTLV-3 diversity likely originating from multiple zoonotic transmissions of divergent STLV-3.     

HTLV infection among foreign pregnant women living in Spain

Background

The overall seroprevalence of HTLV infection among pregnant women in Spain is below 0.02% and accordingly universal antenatal screening is not recommended. However, as the number of immigrants has significantly increased during the last decade, this population might warrant specific considerations.

Objective

To evaluate the seroprevalence of HTLV infection among immigrant pregnant women living in Spain.

Methods

From January 2009 to December 2010 a cross-sectional study was carried out in all foreign pregnant women attended at 14 Spanish clinics. All were tested for HTLV antibodies using a commercial enzyme-immunoassay, being reactive samples confirmed by Western blot or PCR.

Results

A total of 3337 foreign pregnant women were examined. Their origin was as follows: Latin America 1579 (47%), North Africa 507 (16%), East Europe 606 (18%), Sub-Saharan Africa 316 (9%), North America and West Europe 116 (3.5%) and Asia and Australia 163 (5%). A total of 7 samples were confirmed as HTLV positive, of which 6 were HTLV-1 and 1 HTLV-2. HTLV-1 infection was found in 5 women coming from Latin America and 1 from Morocco. The only woman with HTLV-2 came from Ghana. The overall HTLV seroprevalence was 0.2%, being 0.3% among Latin Americans and 0.2% among Africans. It was absent among women coming from other regions.

Conclusions

The seroprevalence of HTLV infection among foreign pregnant women in Spain is 0.2%, being all cases found in immigrants from Latin America and Africa. Given the benefit of preventing vertical transmission, antenatal screening should be recommended in pregnant women coming from these regions.     

Design and development of a quantitative real time PCR assay for monitoring of HTLV-1 provirus in whole blood

BackgroundProviral load quantification of human T-lymphotropic virus type 1 (HTLV-1) is an essential marker for disease progression. Therefore, accurate and precise quantification of the virus is important. However, many articles published about detection and quantification of HTLV-1 virus neither reported any databank for the pre-validation of their primer and probe sequences nor stressed on its importance. Consequently, this failure may cause proviral load measurement variations of different HTLV-1 strains.ObjectiveThe aim of this study was to develop a TaqMan assay for HTLV-1 proviral load quantification which is based on a conserved region of tax gene with minimal sequence variability.Study designFor the purpose of finding the most conserved region of tax gene, all the HTLV-1 Gene Bank records including tax gene sequence (524 records by December 2009) were aligned in order to design on the most conserved region of this gene. The specificity, sensitivity, inter and intra assay and the dynamic range of the assay were experimentally determined by their respective methodology.ResultThe assay has a dynamic range of 10–10⁷ HTLV-1 plasmid DNA/rxn (reaction) and the limit of detection (LOD) less than 10 copies/rxn. The assay gave coefficient of variation (CV) for the Ct values of less than 1% and 4.8% for intra and inter assay, respectively. Clinical sensitivity and specificity were determined to be 97.8% and 100%, respectively.ConclusionThis TaqMan assay is able to reliably quantify proviral load due to the fact that it has been designed on a conserved region of HTLV-1 tax gene with minimal sequence variability.     

Antigenic mixture of synthetic peptides for the immunodiagnosis of HTLV I/II infection

Monomeric and chimeric synthetic peptides were used as coating antigens in four different mixtures in a solid phase immunoassay to select an optimal combination for the detection of antibodies to human T-cell lymphotropic virus (HTLV) in serum samples. The peptides, P-13 (gp21 I), Q5 (gp21 II)-GG-(gp46 II), and Q (gp46 I)-GG-(p19 I), represent immunodominant sequences from transmembrane protein (gp21), envelope protein (gp46), and core protein (p19) of HTLV I/II viruses; they were the most antigenic and specific peptides in previous studies. The sequences of the chimeric peptides were separated by two glycine residues. An indirect UltramicroEnzyme-linked immunosorbent assay (UMELISA) was used to evaluate the antigenicity of these peptide mixtures by using samples from anti-HTLV I/II PRP205(M), (n = 20), HTLV I-infected individuals from Cuba (n = 7), and HTLV I-positive sera from Colombia and Chile (n = 9). The specificity was evaluated with healthy blood donor sera (n = 300), anti-HIV 1-positive samples (n = 10), and other seropositive samples to different infectious agents. The highest sensitivity and specificity was obtained with mixture 1, which could be very useful in the immunodiagnostic of HTLV infection.     

Strong correlation between tax and HBZ mRNA expression in HAM/TSP patients: Distinct markers for the neurologic disease

BackgroundHTLV-1 proviral load is a risk marker for HAM/TSP, but it is insufficient to determine the disease outcome. HTLV-1 Tax and HBZ proteins have been implicated in HAM/TSP pathogenesis in inducing cell proliferation and cytotoxic T lymphocytes response.ObjectivesTo quantify the expression of tax and HBZ mRNA in asymptomatic carriers (AC) and HAM patients, and to investigate their association with HAM/TSP.Study designWe quantified the expression of HTLV-1 tax and HBZ mRNA in 37 AC and 26 HAM patients classified according to proviral load as low (AC_L and HAM_L: <1% infected cells) or high (AC_H and HAM_H: >1%).ResultsThe AC_L subgroup showed the lowest frequency of individuals expressing tax mRNA in comparison with AC_H, HAM_L and HAM_H, and tax mRNA load normalized by proviral load was significantly lower in the AC_L. In turn, normalized HBZ mRNA expression was similar in all subgroups. Both tax and HBZ mRNA expression were moderately correlated with proviral load in AC (r = 0.6, p < 0.001) and were weaker in HAM (r = 0.4, p < 0.05). In contrast, the correlation between tax and HBZ mRNA load was moderate in AC (r = 0.5, p = 0.001) and was much stronger in HAM (r = 0.8, p < 0.001). In addition, HBZ mRNA load, but not tax, was significantly associated with motor disability in HAM patients (p = 0.036).ConclusionsThe expression of tax mRNA seems to be best to estimate the risk of HAM/TSP, whereas HBZ mRNA appears to be a surrogate marker to disease progression, indicating that they have important but distinct roles in HAM/TSP pathogenesis.     

The best algorithm to confirm the diagnosis of HTLV-1 and HTLV-2 in at-risk individuals from São Paulo, Brazil

The ability to confirm the diagnosis of human T-lymphotropic virus types 1 and 2 (HTLV-1 and HTLV-2) in at-risk individuals in São Paulo, Brazil by Western blotting (WB), conventional polymerase chain reaction (tax and pol PCR) and real-time PCR (pol) is compared. Seventy-three blood samples that were reactive in HTLV-1/2 serological screening enzyme immunoassays (EIAs) were evaluated. HTLV-1/2 was confirmed in 53 blood samples: 48 were positive by WB, 41 were positive by PCR and 42 scored positive by real-time PCR assays (37 of 48 WB-positive samples plus five WB-indeterminate samples that were further confirmed by sequencing). Although WB was able to detect more cases of HTLV-1/2 infection, the real-time PCR assay was able to discriminate between these two viruses and confirm an individual HTLV-1/HTLV-2 diagnosis in two HTLV WB-untyped samples and five WB-indeterminate samples. Because of the large number of WB-indeterminate samples and the cost of the WB assay in Brazil, it is proposed an algorithm that employs two EIAs for screening and then real-time PCR to confirm the infection, followed by testing any PCR-negative samples with the WB assay. This strategy reduces costs and improves the accuracy of the diagnosis of HTLV-1/2.     

HTLV III antibodies and immunological alterations in hemophilia patients

Summary The clinical, immunological, and serological status of 28 patients with hemophilia A and of 13 patients with hemophilia B was investigated. Thirty-four patients were treated regularly by clotting factor concentrates and 7 patients had been substituted only 1 to 4 times. Almost all patients with severe hemophilia suffered from hepatopathy. No patient had clinical evidence of the acquired immunodeficiency syndrom (AIDS).Asymptomatic hemophiliacs showed a decreased number of T-helper (OKT 4) cells and an increased number of T-suppressor (OKT 8) cells, which resulted in an inversed OKT 4/OKT 8 cell ratio. Natural killer cell activity of all patients was decreased compared to controls. After culture there was no significant difference of NK cell activity between hemophiliacs and controls. This phenomen was interpreted as a possible maturation defect of NK-cells in vivo.No relationship between immunological alterations and hepatopathy, hepatitis markers, CMV antibodies, amount and source of required factor concentrates, and the kind of hemophilia was observed. IgG immunoglobulins were higher and the OKT 4/OKT 8 ratio lower in the eight patients with lymphadenopathy than in patients without lymphadenopathy. The prevalence of antibodies to human T-lymphotropic virus (HTLV III) was measured in 35 hemophiliacs and in 25 polytransfused patients, most of whom were suffering from acute leukemia. In 8 of 35 hemophiliacs antibodies to HTLV III virus were detected by an enzyme linked immunosorbent assay (ELISA) and confirmatory tests. All seropositive patients were treated by blood products from the United States. Eight hemophiliacs treated by factor concentrates from German donors only were seronegative. In comparison 2 of 25 examined non-hemophilia patients receiving multiple blood products from local donors were seropositive for HTLV III. The results show that hemophilia patients treated by imported clotting factor concentrates have a high risk of HTLV III positivity. Hemophiliacs substituted by blood products obtained by local donor pools have only a small risk of infection. Because non-hemophiliac polytransfused patients had HTLV III antibodies, there must be asymptomatic virus carriers in the local donor pool. The HTLV III antibody screening of all donors and the heat treating of factor concentrates will give better therapeutic safety.Abbreviations AIDS Acquired immunodeficiency syndrome - ALT Alanin-Aminotransferase - Anti-HBc Antibody to hepatitis B core antigen - Anti-HBs Antibody to hepatitis B surface antigen - AST Aspartat-Aminotransferase - CMV Cytomegaly virus - EBV Epstein-Barr-virus - EDTA Ethylendiamintetraacetate - ELISA Enzyme linked immunosorbent assay - -GT Gamma-Glutamyl-Transferase - HBsAg Hepatitis B surface antigen - HLA Human Leukocyte Antigen - HTLV III Human T-lymphotropic virus - IL-2 Interleukin 2 - IPS Immune peroxidase staining - LDH Lactat-Dehydrogenase - LGL Large granular lymphocyte - LU₃₀ Lytic units - MNC Mononuclear cells - NK Natural Killer cells - OKT 3 Total T-cells - OKT 4 T-helper cells - OKT 8 T-suppressor cells     

Immunological and virological investigation in patients with lymphoadenopathy syndrome and in a population at risk for acquired immunodeficiency syndrome (AIDS), with particular focus on the detection of antibodies to human T-lymphotropic retroviruses (HTLV III)

Thirteen patients affected with unexplained lymphoadenopathy, fever, weight loss, and diarrhea (lymphoadenopathy syndrome; LAS) were evaluated for the possible appearance of acquired immunodeficiency syndrome (AIDS) and for immunological and virological characterization. The patients belonged to categories of individuals at risk for AIDS and were homosexual and/or drug abusers or hemophiliacs. Lymph node biopsy showed the histological picture of a follicular hyperplasia. The study of cell-mediated immunity (CMI), humoral immune response, and natural killer (NK) activity demonstrated a significant decrease in T cells with the helper/inducer phenotype (OKT ₄ ⁺ cells) and a relatively increased number of lymphocytes with the suppressor/cytotoxic phenotype (OKT ₈ ⁺ cells). NK activity was significantly lower than in normal controls. Thein vitro response to policlonal activators (phytohemagglutinin; PHA) and the cutaneous responsiveness to recall skin tests were impaired, whereas immunoglobulin production was increased, mainly in the IgG fraction. Virological studies showed high serum antibody titers to cytomegalovirus (CMV) but a lack of specific CMI as assayed by the leukocyte migration inhibition test (LMIT). CMV was also isolated from the urine specimen of one patient. The antibody pattern to Epstein-Barr virus (EBV) showed the uncommon contemporary presence of both Epstein-Barr nuclear antigen (EBNA) and early antigen (EA) antibodies. Antibodies to human T-lymphotropic retroviruses (HTLV III) were positive in 10 patients and the virus was isolated in 3 of them. In some patients the presence of serum antibodies to HTLV III was not associated with an impairment of the immune function. A group of individuals at risk for AIDS without LAS was also evaluated for the presence of HTLV III antibodies; the percentage of positive sera was 11.4. Nevertheless, individuals without specific antibodies had immunological abnormalities resembling those of LAS HTLV III-positive patients. The possible implications of these findings are discussed.     

Defective Human T-Cell Lymphotropic Virus Type I (HTLV-I) Provirus in 10 Chilean Seronegative Patients with Tropical Spastic Paraparesis or HTLV-I-Associated Myelopathy

We studied the presence of tax and ltr genes from human T-cell lymphotropic virus type I (HTLV-I) provirus in the peripheral blood mononuclear cells from 15 seronegative patients with tropical spastic paraparesis or HTLV-I-associated myelopathy by PCR. Only a region of the tax gene from 10 patients was amplified. The nucleotide homologies of six Chilean isolates to the ATK-1 clone ranged between 98.7 and 99.4%.     

The HTLV-1 hbz antisense gene indirectly promotes tax expression via down-regulation of p30(II) mRNA

Human T-cell leukemia virus type 1 (HTLV-1) basic leucine zipper factor (HBZ) is transcribed from the antisense genomic DNA strand and functions differently in its RNA and protein forms. To distinguish between the roles of hbz mRNA and HBZ protein, we generated mutants in a proviral clone that specifically disrupt the hbz gene product. A proviral clone with a splice acceptor mutation that disrupts expression of the predominant hbz mRNA resulted in lower levels of tax mRNA. Heterologous hbz expression restored Tax activity in cells expressing this mutant clone. In contrast, proviral mutants that disrupt HBZ protein did not affect levels of tax mRNA. Expression of hbz resulted in lower levels of p30^II mRNA. Mutation of p30^II overcame the effects of the splice acceptor mutation of hbz, and restored tax expression. Thus, there is a complex interplay of viral regulatory proteins controlling levels of HTLV-1 gene expression.     

Immunological characterization of the low molecular weight gag gene proteins p19 and p15 of human T-cell leukemia-lymphoma virus (HTLV) and demonstration of human natural antibodies to them

Small molecular weight gag gene proteins p19 and p15 of human T-cell leukemia virus (HTLV) were purified to homogeneity from density banded virus, using differential affinities to phosphocellulose at pH 7.9 and 6.5. Using specific radioimmunoassays, p19 and p15 were shown to band with HTLV on sucrose gradients. These proteins were present only in HTLV-I and in cell lines expressing HTLV-I. They were not expressed in a B-cell line from patient CR, although his T cells were HTLV producers. No significant immunological cross-reactivity was detected between these proteins and HTLV-II_MO P19 and p15 did not share any common antigenic determinants with each other or with HTLV p24 in competition radioimmunoassays. Sera of HTLV-positive leukemia-lymphoma patients and some of their relatives also had natural antibodies to p19 and p15.     

HTLV infected individuals have increased B-cell activation and proinflammatory regulatory T-cells

Human T-lymphotropic virus (HTLV) affects the human immune system in many ways, most notably by inducing proliferation of infected CD4 + T cells, but several other cell types are also affected. To characterize the effects of HTLV infection, we analysed blood samples from HTLV-infected individuals by flow cytometry. Samples were collected from visitors at the HIV clinic in Bissau, Guinea-Bissau. These samples were tested for HTLV and HIV, and 199 were analysed by flow cytometry using panels for B cells, T-cell maturation and activation, regulatory T cells (Tregs) and monocytes. CD80+ cell proportions were significantly higher in HTLV infected than in HTLV uninfected in all B cell subsets. Among T cells, there was no change in cell distribution between maturation stages, but a higher CD25+ proportion among Tregs (61.1 % vs 36.3 %, p < 0.001) in HTLV infected than in HTLV uninfected. The level of CD49d on individual cells was also higher (MFI 2734.5 vs 1,041, p < 0.001). In HTLV infected individuals, CD8 + T cells had a lower proportion of CTLA-4+ (2.5 % vs 3.5 %, 0.048) and higher PD1+ proportion on the CD45RO + subset (81.6 % vs 77.1 %, p < 0.001). Together, these findings point toward reduced regulation in HTLV + patients, which leads to immune activation. This study corroborates previous findings and offers new insight into the effects of HTLV by providing a broad flowcytometric analysis of immune cells in HTLV + individuals.     

Evaluation of host genetic and viral factors as surrogate markers for HTLV‐1‐associated myelopathy/tropical spastic paraparesis in Peruvian HTLV‐1‐infected patients

Human T‐lymphotropic virus 1 (HTLV‐1)‐associated myelopathy/tropical spastic paraparesis (HAM/TSP) is a complication that affects up to 5% of HTLV‐1‐infected individuals. Several host genetic and viral factors have been associated with the risk of HAM/TSP. The aim of this study was to evaluate the performance of a prognostic model for HAM/TSP developed in Japan in a Peruvian population of 71 HAM/TSP patients and 94 asymptomatic carriers (ACs). This model included age, proviral load (PVL), the presence of HLA‐A*02 and HLA‐Cw*08 alleles, SDF‐1 +801, and TNF‐α ?863 polymorphisms, and viral subgroup. We describe frequencies for the four host genetic markers and demonstrate the presence of the HTLV‐1 tax B subgroup in Peru. Using cross‐validation, we show that the predictive ability of the prognostic model, as characterized by the area under the receiver‐operating characteristic curve (AUC), does not differ from a model containing PVL only (both AUC = 0.74). We found some suggestive evidence of a protective effect of the HLA‐A*02 allele but failed to replicate the associations with the other three genetic markers and with viral subgroup. A logistic model containing PVL, age, gender, and HLA‐A*02 provided the best predictive ability in the Peruvian cohort (AUC = 0.79). J. Med. Virol. 82:460–466, 2010. © 2010 Wiley‐Liss, Inc.     

Prevalence of antibodies to HTLV in antenatal clinic attenders in South East London

The prevalence of antibodies to HTLV in women attending a south east London antenatal clinic between October 1990 and July 1992 was determined using sera referred for routine rubella antibody testing. Samples were screened for HTLV antibody using a modified Fujirebio gel particle agglutination test and reactive sera confirmed by ELISA (Abbott Laboratories, North Chicago, IL) and two commercial Western blots (Cambridge Biotech Inc., Rockville, MD, and Diagnostic Biotechnology, Genelab Diagnostics, Louvaine, Belgium). This strategy confirmed the presence of HTLV-1 antibodies in 12 out of 6,289 sera (0.19%, 95% confidence limits 0.083% to 0.30%) and HTLV-2 antibodies in 2 (0.03%) sera. Specimens from 8 of 821 (0.97%, 95% confidence limits 0.42% to 1.9%) Afro-Caribbean women, three of 1,136 (0.26%, 95% confidence limits 0.055% to 0.78%) African women, and one of 3,049 (0.033%, 95% confidence limits 0.006% to 0.18%) Caucasian women were positive for HTLV-1 antibodies. Sera from Afro-Caribbean women born in the Caribbean were 7.6 times more likely to be HTLV-1 antibody positive than sera from Afro-Caribbean women born in the UK (P = 0.012). Selective testing of Afro-Caribbean and African antenatal clinic attenders, in this setting, would have identified 11 of the 12 HTLV-1 infections at an estimated cost of prevention of HTLV-1 associated disease of £100,000 per case which is considerably less than the £1.3 million which has been estimated to prevent a case by universal screening of UK blood donors. J. Med. Virol. 52:326–329, 1997. © 1997 Wiley-Liss, Inc.