A collaborative study to establish the 3rd WHO International Standard for hepatitis B virus for nucleic acid amplification techniques.

Nucleic acid amplification techniques (NAT) are routinely used for clinical diagnostics and monitoring hepatitis B virus (HBV) infections, and are implemented on a voluntary basis for blood screening. A collaborative study was performed to evaluate a replacement WHO International Standard for HBV for the standardization of NAT. Two lyophilised HBV candidates were evaluated by 16 laboratories worldwide, alongside the existing HBV International Standard. The overall mean potency estimates for the candidate samples 1 and 2, relative to sample 3 (2nd HBV International Standard), from quantitative assays, were 5.93 and 5.98 log10 International Units (IU)/mL respectively. The variability in individual laboratory mean estimates for samples 1-3 for quantitative assays was ∼0.3 log10 IU/mL. The inter-laboratory variability for qualitative assays was higher. Accelerated thermal degradation studies indicate that both lyophilised candidates are stable and suitable for long-term use. Overall, the results suggested that both candidates were suitable as replacement International Standards. Sample 1 (NIBSC code 10/264) was established as the 3rd WHO International Standard for HBV for NAT with an assigned potency of 850,000 IU/mL (∼5.93 log10 IU/mL), when reconstituted in 0.5 mL of nuclease-free water. It is intended for the calibration (in IU) of secondary reference materials used in HBV NAT.

A collaborative study to establish the 1st WHO International Standard for Epstein-Barr virus for nucleic acid amplification techniques.

Variability in viral load measurements using nucleic acid amplification techniques (NAT) has a significant impact on the management of Epstein-Barr virus (EBV)-associated diseases, and has highlighted a need for standardisation of these measurements. The aim of this collaborative study was to evaluate the suitability of a range of candidate reference materials to harmonise EBV viral load measurements in a wide range of NAT assays. Candidate materials included lyophilised and liquid whole virus preparations of the EBV B95-8 strain, and preparations of Namalwa and Raji cells. Variability between the individual laboratory mean estimates for each candidate was 2.5 log10 copies/mL. The agreement between laboratories was improved when the potency of each candidate was expressed relative to the lyophilised B95-8 preparation. The results of the study indicate the suitability of this candidate as the 1st WHO International Standard for EBV for NAT. It was established in October 2011 by the WHO's Expert Committee on Biological Standardisation with an assigned potency of 5 × 10(6) International Units (IU) (NIBSC code 09/260). It is intended to be used for the calibration of secondary reference materials, used in EBV NAT assays, in IU, thereby improving the comparability of patient viral load measurements.

Are We There Yet? Impact of the First International Standard for Cytomegalovirus DNA on the Harmonization of Results Reported on Plasma Samples.

BACKGROUND: Interassay harmonization of cytomegalovirus (CMV) DNA measurement is important for infection management. Uncertainty exists regarding the result harmonization achievable in patient plasma samples using quantitative polymerase chain reaction (qPCR) assays with calibrators now traceable to the First World Health Organization International Standard (IS) for CMV DNA. METHOD: Serial dilutions of the IS and a blinded panel of 40 genotyped CMV DNA-positive pooled plasma samples and 10 negative plasma samples were tested by 6 laboratories using 10 qPCR assays calibrated to the IS. Each clinical sample was constructed using plasma from a single unique transplant recipient. RESULTS: The variance for individual CMV DNA-positive samples was greater for clinical samples (median, 1.50 [range, 1.22-2.82] log10 IU/mL) than for IS dilutions (median, 0.94 [range, 0.69-1.35] log10 IU/mL) (P < .001); 58.9% of all clinical sample results and 93.6% of IS dilution results fell within ±0.5 log10 IU/mL of the mean viral load of each sample. Result variability was not impacted by either genotype or quantitative levels of CMV DNA. Testing procedure differences can significantly influence results, even when analyte-specific reagents are identical. For clinical samples, all assays demonstrated result bias (P < .008). Assays with amplicon sizes ≤86 bp had significantly higher results compared to assays with larger amplicon sizes (≥105 bp) (P < .001). CONCLUSIONS: The variability in CMV DNA results reported on individual samples has been reduced by the IS, but ongoing clinically relevant variability persists, preventing meaningful interassay result comparison.

A collaborative study to establish the 1st WHO International Standard for human cytomegalovirus for nucleic acid amplification technology.

Variability in the performance of nucleic acid amplification technology (NAT)-based assays presents a significant problem in the diagnosis and management of human cytomegalovirus (HCMV) infections. Here we describe a collaborative study to evaluate the suitability of candidate reference materials to harmonize HCMV viral load measurements in a wide range of NAT assays. Candidate materials comprised lyophilized Merlin virus, liquid Merlin virus, liquid AD169 virus, and purified HCMV Merlin DNA cloned into a bacterial artificial chromosome. Variability in the laboratory mean HCMV concentrations determined for virus samples across the different assays was 2 log10. Variability for the purified DNA sample was higher (>3 log10). The agreement between laboratories was markedly improved when the potencies of the liquid virus samples were expressed relative to the lyophilized virus candidate. In contrast, the agreement between laboratories for the purified DNA sample was not improved. Results indicated the suitability of the lyophilized Merlin virus preparation as the 1st WHO International Standard for HCMV for NAT. It was established in October 2010, with an assigned potency of 5 × 10(6) International Units (IU) (NIBSC code 09/162). It is intended to be used to calibrate secondary references, used in HCMV NAT assays, in IU.

Development of working reference materials for clinical virology.

Nucleic acid amplification technique (NAT)-based assays are replacing traditional diagnostic methods in clinical laboratories. However, many of these assays are developed in-house and the lack of standardised reference materials has hindered assay implementation and control. Consequently, in the UK, the Clinical Virology Network (CVN), the National Institute for Biological Standards and Control (NIBSC), and the Health Protection Agency (HPA), are working in collaboration to develop working standards or 'run controls' for diagnostic NAT-based assays, particularly real-time PCR. These run controls are intended for use in microbiology laboratories and are designed to be extracted and amplified in the same way as clinical samples and included in each assay run. The aim is to enable clinical laboratories to continuously monitor the performance of their diagnostic NAT assays on a run-by-run basis allowing inter-laboratory comparisons, and ultimately improving the consistency of results. At present, eight candidate run controls representing clinically relevant viral targets have been prepared for evaluation by CVN laboratories. Data have been returned on the performance of each run control in routine diagnostic assays. Preliminary results presented here indicate a high level of variability in intra- and inter-assay detection of these targets, highlighting the need for standardisation of assays within molecular diagnostics.

Persistence of novel human parvovirus PARV4 in liver tissue of adults.

Human parvovirus 4 (PARV4) is a recently identified virus whose biology, epidemiology and pathogenic potential have yet to be determined. Recently, it was reported that PARV4 DNA persists in tissues of some HIV-infected individuals, whilst PARV4 DNA was not detected in tissues of subjects not infected with HIV. In the present study, liver tissue from 87 individuals, none of who were infected with HIV, with the exception of a single subject, was analyzed for the presence of PARV4 DNA. Overall, PARV4 DNA was detected in 13 specimens (15%). In other tissues examined, PARV4 genotype 2 (also termed PARV5) DNA was detected in one of four paired bone marrow specimens. Tissue viral loads did not exceed 100 copies per microg of genomic DNA. In addition, serum samples from 40 of these individuals all tested negative for PARV4 DNA. In the subjects analyzed in this study, PARV4 genotype 2 appeared to be genetically more heterogeneous than PARV4 genotype 1. The results show that PARV4 DNA can be detected in liver, and that infection with PARV4 is not restricted to HIV-infected individuals. Previous studies showing the presence of PARV4 in plasma, suggest that during infection with PARV4, a viraemic stage occurs, allowing systemic spread to a variety of tissues.

Analysis of two human parvovirus PARV4 genotypes identified in human plasma for fractionation.

The presence of the novel parvovirus PARV4 and a related variant, PARV5, was recently demonstrated in pooled plasma used in the manufacture of blood and plasma-derived medicinal products. DNA sequence analysis of nearly full-length genomes of four PARV4 and two PARV5 strains from manufacturing plasma pools is now presented. Like PARV4, PARV5 encodes two non-overlapping open reading frames (ORF1 and ORF2), homologous to the non-structural and capsid proteins of other parvoviruses, respectively. A highly conserved region in ORF2 contains phospholipase A2 motifs involved in parvovirus infectivity. Hybridization of strand-specific probes to DNA extracted from high-titre, PARV4-positive plasma revealed that the positive and negative strands are packaged into PARV4 virions in similar quantities. This extended analysis of nearly full-length PARV4 and PARV5 sequences suggests that they are closely related genotypes and the use of a single virus name, PARV4, comprising genotypes 1 and 2 (previously termed PARV5) is proposed.

Frequent detection of the parvoviruses, PARV4 and PARV5, in plasma from blood donors and symptomatic individuals.

BACKGROUND: Plasma pools used in the manufacture of blood- and plasma-derived medicinal products are frequently contaminated with parvovirus B19. The presence of the novel human parvovirus PARV4 and a related variant PARV5 in manufacturing plasma pools was recently demonstrated. Another recently identified parvovirus, human bocavirus (HBoV), has been identified in respiratory samples from children with lower respiratory tract disease. STUDY DESIGN AND METHODS: Recent and archived manufacturing plasma pools, as well as plasma from healthy blood donors (individual donations; pools of 16 donations) and febrile patients, were examined for the presence of PARV4 and PARV5 with conventional and TaqMan polymerase chain reaction assays. In addition, highly sensitive assays were used to examine the presence of HBoV DNA in manufacturing pools. RESULTS: Of 351 recent manufacturing plasma pool samples, 14 (4%) tested positive for the presence of PARV4 and PARV5. This frequency was elevated in the archived pools. Viral loads ranged from less than 100 up to 4 million copies per mL plasma, with some pools containing a mixture of both viruses. In individual plasma samples from healthy blood donors and febrile patients, the frequencies of detection were 2 and 6 percent, respectively. No HBoV sequences were identified in manufacturing plasma pools (n = 167). CONCLUSION: PARV4 and PARV5 are readily detected in manufacturing plasma pools, test pools (constructed from 16 donations), and individual donations derived from healthy blood donors. The prevalence of these viruses was increased in plasma samples from febrile patients. Despite the use of highly sensitive assays for HBoV, it was not possible to identify manufacturing plasma pools containing HBoV sequences.

Effects of probe binding mutations in an assay designed to detect parvovirus B19: implications for the quantitation of different virus genotypes.

Quantitative real-time PCR is being widely used in the identification of plasma donations that contain high levels of parvovirus B19, to ensure their exclusion from start pools used in the manufacture of plasma derived medicinal products. In this study, the primers and probe of one such published assay, are examined for their ability to quantify different genotypes of parvovirus B19. Under standard assay conditions, there is a failure to detect and quantify one genotype 3 subtype. Alterations in assay conditions can restore quantitation of this subtype.

Novel parvovirus and related variant in human plasma.

We report a novel parvovirus (PARV4) and related variants in pooled human plasma used in the manufacture of plasma-derived medical products. Viral DNA was detected by using highly selective polymerase chain reaction assays; 5% of pools tested positive, and amounts of DNA ranged from <500 copies/mL to >106 copies/mL plasma.

Susceptibility of porcine cytomegalovirus to antiviral drugs.

OBJECTIVES: Re-activation of porcine cytomegalovirus (PCMV) in the xenograft has been reported in pig-to-baboon models of xenotransplantation and is associated with invasive disease and consumptive coagulopathy. If xenotransplantation of porcine organs into human recipients is to proceed, donor organs will have to be free from a wide range of infectious agents including PCMV. However, it is prudent to characterize the antiviral susceptibility of this virus. We therefore investigated the effect of selected antiviral agents, currently licensed for the treatment of human herpesvirus infections, on PCMV replication. METHODS: Antiviral susceptibility was determined using real-time PCR and indirect immunofluorescence measurements in a porcine fallopian tube cell line infected with PCMV. RESULTS: PCMV replication was significantly inhibited by ganciclovir and cidofovir (both EC(50) < 1 mg/L) and to a lesser extent by foscarnet (EC(50) within range 25-50 mg/L) and aciclovir (EC(50) > 25 mg/L). CONCLUSIONS: These results show that, if it proves necessary, ganciclovir and cidofovir should be considered as first-line drugs to treat PCMV infections in xenograft recipients.

Porcine cytomegalovirus in pigs being bred for xenograft organs: progress towards control.

In human medicine, human cytomegalovirus (HCMV) is readily transmitted by organ transplant causing end-organ disease and triggering graft rejection in recipients. Because of a chronic shortage of human organs, pigs transgenic for human complement control proteins are being considered as potential donors. Such xenotransplantation raises concerns about the potential zoonotic transmission of viruses including porcine cytomegalovirus (PCMV), an endemic infection of pigs. Similar to HCMV and PCMV transmission is thought to occur in utero and perinatally. We used quantitative polymerase chain reaction to examine the prevalence, organ distribution and viral load of PCMV in human decay accelerating factor (CD55) transgenic pigs. In animals reared under conventional farm conditions, virus was identified in a wide range of organs including potential xenografts (liver, kidney and heart). The spleen was PCMV DNA positive in all infected pigs. Examination of foetal spleens failed to identify evidence of transplacental infection and prospective monitoring of two litters showed that infection occurred in the postnatal period. This transmission was prevented by hysterotomy derivation and barrier rearing. Our findings demonstrate that PCMV could be eradicated from pig herds being bred for xenotransplantation and argue that the spleen from donor animals should be examined as part of quality control procedures if clinical trials proceed.