Calibrated real-time PCR for evaluation of parvovirus b19 viral load

Quantitative nucleic acid amplification methods and their implications in clinical virology

Recently, a number of techniques have been approved for quantification of viral nucleic acids in clinical samples. Viral load (VL) tests have considerable importance in the management of patients and are widely used in routine diagnosis. In clinical virology, VL testing are important to monitor the antiviral treatment, to initiate preemptive therapy, to understand pathogenesis, and to evaluate the infectivity. These tests have now become a part of many diagnostic and treatment guidelines. Considering the various challenges for in-house viral testing related to the standardization, validation, and precision; they are gradually being replaced by the United States Food and Drug Administration (US FDA) cleared tests. This review summarizes the various viral quantification methods and also discusses the clinical applicability of these in human immunodeficiency virus, Hepatitis B virus, Hepatitis C virus, Cytomegalovirus, and Epstein Barr virus infected patients. Further the challenges and future perspectives of VL testing have also been discussed.

Parvovirus B19 Replication and Expression in Differentiating Erythroid Progenitor Cells

The pathogenic Parvovirus B19 (B19V) is characterized by a strict adaptation to erythroid progenitor cells (EPCs), a heterogeneous population of differentiating cells with diverse phenotypic and functional properties. In our work, we studied the dynamics of B19V infection in EPCs in dependence on the cell differentiation stage, in terms of distribution of infected cells, synthesis of viral nucleic acids and production of infectious virus. EPCs at early differentiation stage led to an abortive infection, without viral genome replication and a very low transcriptional activity. EPCs at later stages were permissive, with highest levels of viral replicative activity at day 9 (+3.0 Log from 2 to 48 hpi) and lower levels at day 18 (+1.5 Log from 2 to 48 hpi). B19V DNA increment was in accordance with the percentage of cells positive to flow-FISH assay (41.4% at day 9, 1.1% at day 18). Quantitation of total RNA indicated a close association of genome replication and transcription with viral RNA accumulation within infected cells related to viral DNA increase during the course of infection. Analysis of the different classes of mRNAs revealed two distinct pattern of genome expression profile with a fine regulation in the frequency utilization of RNA processing signals: an early phase, when cleavage at the proximal site leading to a higher relative production of mRNA for NS protein, and a late phase, when cleavage at the distal site was more frequent leading to higher relative abundance of mRNA for VP and 11 kDA proteins. Infectious virus was released from cells at day 6–15, but not at day 18. Our results, providing a detailed description of B19V replication and expression profile in differentiating EPCs, highlight the very tight adaptation of B19V to a specific cellular target defined both by its erythroid lineage and its differentiation stage.

Parvovirus B19 at the culprit coronary stenosis predicts outcome after stenting

BACKGROUND

Parvovirus (PV) B19 DNA is detected in endothelial cells and may cause endothelial dysfunction, which is involved in in-stent restenosis. We aimed at performing an exploratory analysis that evaluated if PVB19 DNA at the culprit coronary stenosis would be associated with an increased rate of major adverse cardiac events (MACE) after coronary stenting.

MATERIALS AND METHODS

Consecutive patients undergoing stent implantation for stable or unstable coronary artery disease were enroled. Serology for PVB19 infection and presence of DNA for PVB19 on balloons used for predilatation were assessed in all patients. MACE rate, as a composite of cardiac death, myocardial infarction (MI) or clinically driven target lesion revascularization (TLR) was obtained at 24 month follow-up. Adjusted hazard ratio (HR) with 95% confidence interval (CI) was calculated for variables associated with MACE.

RESULTS

One hundred and nine patients [age 66 ± 10, male sex 89 (82%)] were enroled. At 24-month follow-up, 18 patients experienced a MACE. Two patients (2%) experienced MI, while 16 patients (15%) experienced clinically driven TLR. At multiple Cox regression analysis, the presence of PVB19 DNA on the balloon and the use of bare-metal stents were independent predictors of MACE [HR 3·30, 95% CI (1·12-10·08), P = 0·03 and HR 4·19, 95% CI (1·60-10·94), P = 0·003].

CONCLUSIONS

PVB19 DNA detected on the balloon used for dilatation of coronary stenosis before stent implantation is associated with MACE rate at follow-up, mainly due to clinically driven TLR. The results of this exploratory analysis should be confirmed in a larger population.

The quantitative real-time polymerase chain reaction for the analysis of plant gene expression

The quantitative real-time polymerase chain reaction is used to simultaneously amplify and quantify a targeted DNA molecule. It can be used to determine exact copy number of a molecule within a sample and/or to compare the quantity of a molecule between samples. When combined with reverse transcription, it is a powerful tool for the analysis of gene expression, and it is widely used for this purpose in plant species. Here we provide an introduction to fundamental concepts relevant for the analysis of gene expression in plants using this technique and a protocol for quantification of the relative expression of a sucrose phosphate synthase gene along the maturation gradient of a sugarcane leaf.

Keeping pace with parvovirus B19 genetic variability: a multiplex genotype-specific quantitative PCR assay

Three genotypes have been identified within the parvovirus B19 species (B19V), and such genetic diversity may have significant implications for the development of molecular detection assays. In the present study, B19V genetic variability has been examined on a subset of genomic sequences available in the NCBI nucleotide database, and a quantitative PCR (qPCR) assay able to detect, differentiate, and quantify all viral variants has been established. The designed primers and probes have been used for the development of alternative detection formats, based on a combined use of intercalating dye and genotype-specific hydrolysis probes. The qPCR assay analytical performances have been determined on the 1st WHO International Reference Panel for Parvovirus B19 Genotypes. The developed qPCR protocols allow for the detection of genotypes 1 to 3 with equal accuracy, and with a limit of detection (LOD) of 200 IU/ml. A comparison of routine performance was carried out with respect to a previously established assay specifically validated on B19V genotype 1. For 130 clinical samples analyzed, 126 showed concordant results (31 positive and 97 negative), while 4 showed discordant results. Overall, the genotype-specific qPCR assay showed a sensitivity of 93.94% and a specificity of 97.94%, with an agreement rate of 96.92%. The proposed qPCR assay and the alternative protocols developed, each with robust performance, may allow choice with respect to operational systems and diagnostic requirements and might contribute to provide a more reliable diagnostic service and epidemiological surveillance of B19 virus.

Parvovirus B19 Achievements and Challenges

Parvovirus B19 is a widespread human pathogenic virus, member of the Erythrovirus genus in the Parvoviridae family. Infection can be associated with an ample range of pathologies and clinical manifestations, whose characteristics and outcomes depend on the interplay between the pathogenetic potential of the virus, its adaptation to different cellular environments, and the physiological and immune status of the infected individuals. The scope of this review is the advances in knowledge on the biological characteristics of the virus and of virus-host relationships; in particular, the interactions of the virus with different cellular environments in terms of tropism and ability to achieve a productive replicative cycle, or, on the contrary, to establish persistence; the consequences of infection in terms of interference with the cell physiology; the process of recognition of the virus by the innate or adaptive immune system, hence the role of the immune system in controlling the infection or in the development of clinical manifestations. Linked to these issues is the continuous effort to develop better diagnostic algorithms and methods and the need for development of prophylactic and therapeutic options for B19V infections.

Parvovirus b19 DNA CpG dinucleotide methylation and epigenetic regulation of viral expression

CpG DNA methylation is one of the main epigenetic modifications playing a role in the control of gene expression. For DNA viruses whose genome has the ability to integrate in the host genome or to maintain as a latent episome, a correlation has been found between the extent of DNA methylation and viral quiescence. No information is available for Parvovirus B19, a human pathogenic virus, which is capable of both lytic and persistent infections. Within Parvovirus B19 genome, the inverted terminal regions display all the characteristic signatures of a genomic CpG island; therefore we hypothesised a role of CpG dinucleotide methylation in the regulation of viral genome expression.

The analysis of CpG dinucleotide methylation of Parvovirus B19 DNA was carried out by an aptly designed quantitative real-time PCR assay on bisulfite-modified DNA. The effects of CpG methylation on the regulation of viral genome expression were first investigated by transfection of either unmethylated or in vitro methylated viral DNA in a model cell line, showing that methylation of viral DNA was correlated to lower expression levels of the viral genome. Then, in the course of in vitro infections in different cellular environments, it was observed that absence of viral expression and genome replication were both correlated to increasing levels of CpG methylation of viral DNA. Finally, the presence of CpG methylation was documented in viral DNA present in bioptic samples, indicating the occurrence and a possible role of this epigenetic modification in the course of natural infections.

The presence of an epigenetic level of regulation of viral genome expression, possibly correlated to the silencing of the viral genome and contributing to the maintenance of the virus in tissues, can be relevant to the balance and outcome of the different types of infection associated to Parvovirus B19.

Gestational and fetal outcomes in B19 maternal infection: a problem of diagnosis

Parvovirus B19 infection during pregnancy is a potential hazard to the fetus because of the virus' ability to infect fetal erythroid precursor cells and fetal tissues. Fetal complications range from transitory fetal anemia and nonimmune fetal hydrops to miscarriage and intrauterine fetal death. In the present study, 72 pregnancies complicated by parvovirus B19 infection were followed up: fetal and neonatal specimens were investigated by serological and/or virological assays to detect fetal/congenital infection, and fetuses and neonates were clinically evaluated to monitor pregnancy outcomes following maternal infection. Analysis of serological and virological maternal B19 markers of infection demonstrated that neither B19 IgM nor B19 DNA detected all maternal infections. IgM serology correctly diagnosed 94.1% of the B19 infections, while DNA testing correctly diagnosed 96.3%. The maximum sensitivity was achieved with the combined detection of both parameters. B19 vertical transmission was observed in 39% of the pregnancies, with an overall 10.2% rate of fetal deaths. The highest rates of congenital infections and B19-related fatal outcomes were observed when maternal infections occurred by the gestational week 20. B19 fetal hydrops occurred in 11.9% of the fetuses, and 28.6% resolved the hydrops with a normal neurodevelopment outcome at 1- to 5-year follow-up. In conclusion, maternal screening based on the concurrent analysis of B19 IgM and DNA should be encouraged to reliably diagnose maternal B19 infection and correctly manage pregnancies at risk.

Gastrointestinal lesions in parvovirus B19 infection

A 13-year-old girl with persistent fever, pharyngitis, acute anaemia, peripheral blood and bone marrow positive for parvovirus B19 DNA.Microscopic findings of gastrointestinal biopsy showed diffuse vacuolar alteration of the cytoplasma of duodenal enterocytes and virological analysis demonstrated the presence of parvovirus in lymphocytes of the duodenal wall's epithelial layer.In unexplained gastrointestinal pathologies, the role of parvovirus B19 infection should be investigated.

Parvovirus b19 infection localized in the intestinal mucosa and associated with severe inflammatory bowel disease

Infection by human parvovirus B19 is widespread and can be associated with a wide range of different pathologies and clinical manifestations. We provide the first evidence of localization of an active parvovirus B19 infection in the intestinal mucosa and its association with a severe inflammatory bowel disease, characterized by duodenal villous atrophy with increased intraepithelial lymphocytes and inflammatory infiltrates in the colonic mucosa. Virus in the intestinal mucosa was detected in cells of the inflammatory infiltrate, identified as T lymphocytes and selectively localized in sites of active tissue degeneration.

HepG2 hepatocellular carcinoma cells are a non-permissive system for B19 virus infection

Parvovirus B19 has been associated with liver dysfunction and has been considered a potential aetiological agent of fulminant hepatitis and hepatitis-associated aplastic anaemia. The possible effects of B19 virus infection on the liver have been investigated using HepG2 hepatocellular carcinoma cells as a model system, but the reported results are inconsistent. To investigate this relationship further, this study followed the course of B19 virus infection of HepG2 cells in terms of viral DNA, RNA and protein production by quantitative PCR, RT-PCR and immunofluorescence assays. The data showed that B19 virus is able to bind and possibly enter HepG2 cells, but that viral genome replication or transcription is not supported and that viral proteins are not produced. As far as HepG2 cells can be considered a representative model system, any possible pathogenic role of B19 virus on the liver cannot be ascribed to infection or to a direct cytopathic effect on hepatocytes.

Meningoencephalitis with persistent parvovirus B19 infection in an apparently healthy woman

A case of meningoencephalitis, associated with persistent parvovirus B19 infection, is described in a 36-year-old immunocompetent woman. Parvovirus B19 DNA was detected in samples of cerebrospinal fluid and serum; no parvovirus B19-specific clinical symptoms were seen, but neurological episodes were observed in the presence of parvovirus B19 infection and despite the onset of a specific immune response.

Competitive PCR-ELISA protocols for the quantitative and the standardized detection of viral genomes

Competitive PCR-ELISA combines competitive PCR with an ELISA to allow quantitative detection of PCR products. It is based on the inclusion of an internal standard competitor molecule that is designed to differ from the target by a short sequence of nucleotides. Once such a competitor molecule has been designed and constructed, target and competitor sequences are concurrently PCR-amplified, before hybridization to two different specific probes and determination of their respective OD values by ELISA. The target can be quantified in relation to a titration curve of different dilutions of the competitor. The competitor can alternatively be used at a unique optimal concentration to allow for standardized detection of the target sequence. PCR-ELISA can be performed in 1 d in laboratories without access to a real-time PCR thermocycler. This technique is applied in diagnostics to monitor the course of infections and drug efficacy. Competitive PCR-ELISA protocols for the quantitative and for the standardized detection of parvovirus B19 are detailed here as an example of the technique.

Parvovirus B19 genome as a single, two-state replicative and transcriptional unit

The variation in the amount of parvovirus B19 DNA and different classes of RNA in permissive and non-permissive infected cells was analysed by means of quantitative real-time PCR and RT-PCR assays. In the permissive bone marrow mononuclear cells, UT7/Epo and KU812Ep6 cells, viral DNA usually increased within 48 hpi, rarely exceeding 2 Logs with respect to input DNA. Viral RNA was always present within 2-6 hpi, its increase paralleled that of viral DNA up to 36-48 hpi, and all the different classes of viral RNA were constantly represented in stable relative amounts throughout the infection cycle. In the non-permissive TF-1 cells, viral DNA did not increase and only one most represented single class of viral RNA was detected. Our data do not support the current model for B19 virus replication and transcription, consisting in different early and late expression patterns, but suggest an alternative model, indicating that the B19 virus genome should be considered a single, two-state replicative and transcriptional unit.

Detection and monitoring of virus infections by real-time PCR

The employment of polymerase chain reaction (PCR) techniques for virus detection and quantification offers the advantages of high sensitivity and reproducibility, combined with an extremely broad dynamic range. A number of qualitative and quantitative PCR virus assays have been described, but commercial PCR kits are available for quantitative analysis of a limited number of clinically important viruses only. In addition to permitting the assessment of viral load at a given time point, quantitative PCR tests offer the possibility of determining the dynamics of virus proliferation, monitoring of the response to treatment and, in viruses displaying persistence in defined cell types, distinction between latent and active infection. Moreover, from a technical point of view, the employment of sequential quantitative PCR assays in virus monitoring helps identifying false positive results caused by inadvertent contamination of samples with traces of viral nucleic acids or PCR products. In this review, we provide a survey of the current state-of-the-art in the application of the real-time PCR technology to virus analysis. Advantages and limitations of the RQ-PCR methodology, and quality control issues related to standardization and validation of diagnostic assays are discussed.

Slow clearance of human parvovirus B19 viremia following acute infection

Parvovirus B19 is a common, clinically significant pathogen. Reassessment of the viral kinetics after acute infection showed that the virus is not rapidly cleared from healthy hosts, despite early resolution of symptoms. These findings challenge our current conception of the virus' pathogenesis and have implications for the management of the infection.

Recurrent Erythema in Patients with Long-Term Parvovirus B19 Infection

We describe 3 patients with long-term parvovirus B19 infection (defined as detectable parvovirus B19 DNA load for >6 months after the onset of symptoms), which we monitored by serial testing for parvovirus B19 load and the presence of parvovirus B19-specific antibodies in blood. The patients showed recurrent erythema at intervals of several months.