Practical experience of high throughput real time PCR in the routine diagnostic virology setting

Wastewater-based epidemiology for monitoring enteric viruses: a case study in Valladolid, Spain (2020-2021)

Wastewater-based epidemiology (WBE) has been employed for decades and gained renewed significance with the emergence of SARS-CoV-2 at the end of 2019. The incidence of foodborne outbreaks has increased in recent decades, particularly those causing gastroenteritis and diarrhea, which are often of viral origin. However, because many enteric viruses are difficult or uncommon to diagnose, their frequency is often underestimated in comparison to bacterial diseases. WBE provides a valuable alternative for monitoring the presence and evolution of different enteric viruses within a population. This study monitored the major enteric viruses that are potential hazards to public health, including human noroviruses genogroup I and II (NoV GI and GII), human astroviruses (HastV), rotaviruses (RV), and hepatitis A (HAV) and E (HEV) viruses. Viral concentration was performed using an aluminum-based precipitation method, followed by RNA extraction and RT-qPCR quantification. Surveillance was conducted during the COVID-19 pandemics, from October 2020 to October 2021 in Valladolid, Spain, and its surrounding areas. The results showed that both genogroups of noroviruses exhibited the highest normalized concentration levels (5.42 ± 0.08 and 5.44 ± 0.09 Log gc/L, respectively). They were followed by RV (4.41 ± 0.07 Log gc/L) and HastV (6.00 ± 0.11 Log gc/L). Positivity rates were also greater for noroviruses, especially NoVGII (62% and 83.30%, respectively). However, in this case, RV presented a slightly higher positivity rate (46.70%) than HastV (41.30%). Meanwhile, HEV was detected only once (0.67% positivity), and HAV was absent throughout the study period. Additionally, lower concentration levels of the monitored pathogens were detected, compared to later periods, likely because of public health measures implemented during the COVID-19 pandemic. In conclusion, these findings highlight the potential of WBE for the early detection and monitoring of enteric virus outbreaks, particularly during public health crises.

Technical validation of a multiplex real-time PCR for combined detection of Rift Valley fever, chikungunya, Zika and dengue viruses

Several arthropod-borne (arbo)-viruses have overlapping symptoms, insect vectors and geographical occurrence. With little known about the importance of arboviruses as cause of acute undifferentiated fever (AUF) in East and Central Africa (ECA), there is a clear need for a multiplex-PCR allowing for multi-pathogen surveillance. A multiplex real-time RT-PCR (RDCZ-multiplex) was developed and validated for the simultaneous detection of Rift Valley fever virus (RVFV), dengue virus 1-4 (DENV), chikungunya virus (CHIKV) and Zika virus (ZIKV). Phocine distemper virus (PDV) was added to the PCR as sample extraction control. Validation was conducted following the MIQE-guidelines using a panel of retrospective clinical samples and Quality Control for Molecular Diagnostics (QCMD, https://www.qcmd.org/en/) samples with the simplex-PCR as reference. These included samples from RVFV in animals (n = 19), DENV (n = 15), CHIKV (n = 11), ZIKV (n = 2) and YFV (n = 1, QCMD), and 14 negative endemic controls. Extractions and PCRs were done with commercially available kits. Some loss of sensitivity was observed at low target concentrations for RVFV, DENV1 and DENV4, when comparing the standard curves of simplex-PCRs with the multiplex-PCR. The limit of detection of the multiplex-PCR was 2064 copies/ml for CHIKV, 3587 copies/ml for DENV1, 30,249 copies/ml for ZIKV and 73 PFU/ml for RVFV. Specificity of the multiplex-PCRs was 100 %. For 12 out of 48 positive samples with high Cq values, RVFV (n = 7), CHIKV (n = 2), DENV1 (n = 2), YFV (n = 1), the multiplex-PCRs were negative. Although PCR sensitivity of the RDCZ-multiplex is slightly lower with low target concentrations, it offers a useful tool for molecular surveillance and clinical diagnosis for arboviruses for the ECA-region.

The Impact of the Variability of RT-qPCR Standard Curves on Reliable Viral Detection in Wastewater Surveillance

Quantitative Polymerase Chain Reaction (qPCR) is a molecular technique that has become a gold standard in various disciplines, including environmental microbiology, due to its high sensitivity and specificity. In recent years, it has been extensively used in wastewater-based epidemiology to monitor the prevalence of different viruses in the population. In this study, we evaluated whether the no inclusion of a standard curve in each single experiment to reduce time and costs could have an impact on the accuracy of the results. Thirty independent RT-qPCR standard curve experiments using quantitative synthetic RNA material were conducted for seven different viruses, which include two targets of the novel SARS-CoV-2, hepatitis A and E, noroviruses genogroups I and II, human astrovirus, and rotavirus. Results showed that although all the viruses presented adequate efficiency rates (>90%), variability was also observed between them, independently of the viral concentration tested. NoVGII was the virus that presented the higher inter-assay variability in terms of efficiency while showing better sensitivity. In terms of heterogeneity in results, the two targets of SARS-CoV-2 showed the highest rates, being N2 the gene that presented the largest variability (CV 4.38-4.99%) and the lowest efficiency (90.97%). These findings indicate that including a standard curve in every experiment is recommended to obtain reliable results.

A review of nucleic acid-based detection methods for foodborne viruses: Sample pretreatment and detection techniques

Viruses are major pathogens that cause food poisoning when ingested via contaminated food and water. Therefore, the development of foodborne virus detection technologies that can be applied throughout the food distribution chain is essential for food safety. A common nucleic acid-based detection method is polymerase chain reaction (PCR), which has become the gold standard for monitoring food contamination by viruses due to its high sensitivity, and availability of commercial kits. However, PCR-based methods are labor intensive and time consuming, and are vulnerable to inhibitors that may be present in food samples. In addition, the methods are restricted with regard to site of analysis due to the requirement of expensive and large equipment for sophisticated temperature regulation and signal analysis procedures. To overcome these limitations, optical and electrical readout biosensors based on nucleic acid isothermal amplification technology and nanomaterials have emerged as alternatives for nucleic acid-based detection of foodborne viruses. Biosensors are promising portable detection tools owing to their easy integration into compact platforms and ability to be operated on-site. However, the complexity of food components necessitates the inclusion of tedious preprocessing steps, and the lack of stability studies on residual food components further restricts the practical application of biosensors as a universal detection method. Here, we summarize the latest advances in nucleic acid-based strategies for the detection of foodborne viruses, including PCR-based and isothermal amplification-based methods, gene amplification-free methods, as well as food pretreatment methods. The principles, strengths/disadvantages, and performance of each method, problems to be solved, and future prospects for the development of a universal detection method are discussed.

Development, Evaluation, and Clinical Application of PRRSV-2 Vaccine-like Real-Time RT-PCR Assays

In this study, we developed and validated (1) singleplex real-time RT-PCR assays for specific detection of five PRRSV-2 MLV vaccine viruses (Ingelvac MLV, Ingelvac ATP, Fostera, Prime Pac, and Prevacent) and (2) a four-plex real-time RT-PCR assay (IngelvacMLV/Fostera/Prevacent/XIPC) including the internal positive control XIPC for detecting and distinguishing the three most commonly used vaccines in the USA (Prevacent, Ingelvac MLV, and Fostera). The singleplex and 4-plex vaccine-like PCRs and the reference PCR (VetMAXTM PRRSV NA&EU, Thermo Fisher Scientific, Waltham, MA, USA) did not cross-react with non-PRRSV swine viral and bacterial pathogens. The limits of detection of vaccine-like PCRs ranged from 25 to 50 genomic copies/reactions. The vaccine-like PCRs all had excellent intra-assay and inter-assay repeatability. Based on the testing of 531 clinical samples and in comparison to the reference PCR, the diagnostic sensitivity, specificity, and agreement were in the respective range of 94.67-100%, 100%, and 97.78-100% for singleplex PCRs and 94.94-100%, 100%, and 97.78-100% for the 4-plex PCR, with a CT cutoff of 37. In addition, 45 PRRSV-2 isolates representing different genetic lineages/sublineages were tested with the vaccine-like PCRs and the results were verified with sequencing. In summary, the vaccine-like PCRs specifically detect the respective vaccine-like viruses with comparable performances to the reference PCR, and the 4-plex PCR allows to simultaneously detect and differentiate the three most commonly used vaccine viruses in the same sample. PRRSV-2 vaccine-like PCRs provide an additional tool for detecting and characterizing PRRSV-2.

Diagnostic Approaches For COVID-19: Lessons Learned and the Path Forward

Coronavirus disease 2019 (COVID-19) is a transmitted respiratory disease caused by the infection of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Although humankind has experienced several outbreaks of infectious diseases, the COVID-19 pandemic has the highest rate of infection and has had high levels of social and economic repercussions. The current COVID-19 pandemic has highlighted the limitations of existing virological tests, which have failed to be adopted at a rate to properly slow the rapid spread of SARS-CoV-2. Pandemic preparedness has developed as a focus of many governments around the world in the event of a future outbreak. Despite the largely widespread availability of vaccines, the importance of testing has not diminished to monitor the evolution of the virus and the resulting stages of the pandemic. Therefore, developing diagnostic technology that serves as a line of defense has become imperative. In particular, that test should satisfy three criteria to be widely adopted: simplicity, economic feasibility, and accessibility. At the heart of it all, it must enable early diagnosis in the course of infection to reduce spread. However, diagnostic manufacturers need guidance on the optimal characteristics of a virological test to ensure pandemic preparedness and to aid in the effective treatment of viral infections. Nanomaterials are a decisive element in developing COVID-19 diagnostic kits as well as a key contributor to enhance the performance of existing tests. Our objective is to develop a profile of the criteria that should be available in a platform as the target product. In this work, virus detection tests were evaluated from the perspective of the COVID-19 pandemic, and then we generalized the requirements to develop a target product profile for a platform for virus detection.

Standardization of an in-house multiplex real-time polymerase chain reaction for the simultaneous detection of Toxoplasma gondii, Rubella virus, cytomegalovirus, herpes simplex Virus 1 and 2, and Treponema pallidum infection among pregnant women

Background

An in-house multiplex real-time polymerase chain reaction (PCR) was developed in two cocktails for the identification of six Toxoplasma gondii, Rubella virus, cytomegalovirus, herpes simplex virus (1 and 2), and Treponema pallidum (syphilis) (TORCH-S) agents, which causes congenital infection among pregnant women.

Objective

Standardization and validation of an in-house multiplex real-time PCR assay for the detection of TORCH-S infection.

Methods

This study was conducted from February 2017 to February 2019. Primers specific for T. gondii, Rubella virus, cytomegalovirus, herpes simplex virus (1 and 2), and T. pallidum were designed using Primer3 software (https://bioinfo.ut.ee/primer3-0.4.0/). The primer sequences obtained were subjected to BLAST analysis using BLAST database. Synthetic DNA was obtained to use as positive control templates for all the six TORCH-S agents. The lower limit of the detection was performed using plasmid construct for each virus serially diluted from 10^-1 to 10^-9.

Results

An in-house multiplex real-time PCR was standardized and validated in two cocktails for TORCH-S agents, cocktail-1 (HSV1, rubella, and T. gondii), and cocktail-2 (HSV2, CMV, and T. pallidum). The lower limit of the detection for HSV1, rubella, and Toxoplasma were 60.7 copies/10 μl input, 76.4 copies/10 μl input, and 34.4 copies/10 μl input and for HSV2, CMV, and T. pallidum were 80.8 copies/10 μl input, 166 copies/10 μl input, and 43.7 copies/10 μl input, respectively.

Conclusion

TORCH-S infection is one of the significant reasons for irregular pregnant outcomes. It is absolutely important to screen TORCH-S infection for women who had the histories of abnormal pregnancies to prevent birth defects and perinatal complications. This multiplex real-time PCR assay provides a rapid, sensitive, and specific technique to detect these six TORCH-S agents.

Development and Validation of Two Diagnostic Real-Time PCR (TaqMan) Assays for the Detection of Bordetella avium from Clinical Samples and Comparison to the Currently Available Real-Time TaqMan PCR Assay

Bordetella avium (BA) is one of many pathogens that cause respiratory diseases in turkeys. However, other bacterial species can easily overgrow it during isolation attempts. This makes confirming the diagnosis of BA as the causative agent of turkey coryza more difficult. Currently, there are two PCR assays for the molecular detection of BA. One is conventional gel-based PCR and the other is TaqMan real-time PCR (qPCR) assay. However, multiple pitfalls were detected in both assays regarding their specificity, sensitivity, and efficiency, which limits their utility as diagnostic tools. In this study, we developed and validated two TaqMan qPCR assays and compared their performance to the currently available TaqMan qPCR. The two assays were able to correctly identify all BA isolates and showed negative results against a wide range of different microorganisms. The two assays were found to have high efficiency with a detection limit of approximately 1 × 10³ plasmid DNA Copies/mL with high repeatability and reproducibility. In comparison to the currently available TaqMan qPCR assay, the newly developed assays showed significantly higher PCR efficiencies due to superior primers and probes design. The new assays can serve as a reliable tool for the sensitive, specific, and efficient diagnosis of BA.

A comprehensive review on plasmonic-based biosensors used in viral diagnostics

The proliferation and transmission of viruses has become a threat to worldwide biosecurity, as exemplified by the current COVID-19 pandemic. Early diagnosis of viral infection and disease control have always been critical. Virus detection can be achieved based on various plasmonic phenomena, including propagating surface plasmon resonance (SPR), localized SPR, surface-enhanced Raman scattering, surface-enhanced fluorescence and surface-enhanced infrared absorption spectroscopy. The present review covers all available information on plasmonic-based virus detection, and collected data on these sensors based on several parameters. These data will assist the audience in advancing research and development of a new generation of versatile virus biosensors.

Comparative Evaluation of In-House and Commercial Real-Time PCR Methods for the Detection of the BK and JC Viruses in Clinical Samples

Aim  The two most common human polyomaviruses are the BK (BKV) and JC viruses (JCV). Diseases associated with polyomavirus usually occur in cases of severe cellular immunosuppression. BKV and JCV can cause many diseases, especially if they are reactivated in an immunosuppressed host. The aim of this study is to compare and evaluate the results of real-time polymerase chain reaction (PCR) methods targeting the small and large T gene regions of the viral genome, considering polymorphisms occurring in the viral genome of BKV and JCV.

Materials and Methods  Urinary specimens of 82 patients were taken from immunosuppressed patient and sent to molecular microbiology laboratory of Meram Medical Faculty. The small t gene was investigated using a commercial kit (LightMix, Roche) by real-time PCR method. Large T gene was investigated by using the optimized in-house real-time PCR method. Sequence analysis was accepted as the standard method.

Results  BKV positivity was detected in 9 samples and JCV positivity in 61 samples by real-time PCR method specific to small t gene region; BKV positivity in 21 samples and JCV positivity in 67 samples were determined by real-time PCR method specific to the large T gene region. Statistically, there was a significant difference for BKV, but not significant difference for JCV detection between the two methods.

Conclusion  Different polymorphisms in the target gene regions were responsible for the different outcomes obtained from this study. With this sensitivity and specificity, in-house PCR method which we used is a candidate for routine diagnosis.

Primer design for quantitative real-time PCR for the emerging Coronavirus SARS-CoV-2

In December 2019, a new coronavirus disease (COVID-19) outbreak occurred in Wuhan, China. Severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2), which is the seventh coronavirus known to infect humans, is highly contagious and has rapidly expanded worldwide since its discovery. Quantitative nucleic acid testing has become the gold standard for diagnosis and guiding clinical decisions regarding the use of antiviral therapy. However, the RT-qPCR assays targeting SARS-CoV-2 have a number of challenges, especially in terms of primer design. Primers are the pivotal components of a RT-qPCR assay. Once virus mutation and recombination occur, it is difficult to effectively diagnose viral infection by existing RT-qPCR primers. Some primers and probes have also been made available on the WHO website for reference. However, no previous review has systematically compared the previously reported primers and probes and described how to design new primers in the event of a new coronavirus infection. This review focuses on how primers and probes can be designed methodically and rationally, and how the sensitivity and specificity of the detection process can be improved. This brief review will be useful for the accurate diagnosis and timely treatment of the new coronavirus pneumonia.

Human metapneumovirus prevalence and patterns of subgroup persistence identified through surveillance of pediatric pneumonia hospital admissions in coastal Kenya, 2007-2016

BACKGROUND

Human metapneumovirus (HMPV) is an important respiratory pathogen that causes seasonal epidemics of acute respiratory illness and contributes significantly to childhood pneumonia. Current knowledge and understanding on its patterns of spread, prevalence and persistence in communities in low resource settings is limited.

METHODS

We present findings of a molecular-epidemiological analysis of nasal samples from children < 5 years of age admitted with syndromic pneumonia between 2007 and 2016 to Kilifi County Hospital, coastal Kenya. HMPV infection was detected using real-time RT-PCR and positives sequenced in the fusion (F) and attachment (G) genes followed by phylogenetic analysis. The association between disease severity and HMPV subgroup was assessed using Fisher's exact test.

RESULTS

Over 10 years, 274/6756 (4.1%) samples screened were HMPV positive. Annual prevalence fluctuated between years ranging 1.2 to 8.7% and lowest in the recent years (2014-2016). HMPV detections were most frequent between October of one year to April of the following year. Genotyping was successful for 205/274 (74.8%) positives revealing clades A2b (41.0%) and A2c (10.7%), and subgroups B1 (23.4%) and B2 (24.9%). The dominance patterns were: clade A2b between 2007 and 11, subgroup B1 between 2012 and 14, and clade A2c in more recent epidemics. Subgroup B2 viruses were present in all the years. Temporal phylogenetic clustering within the subgroups for both local and global sequence data was seen. Subgroups occurring in each epidemic season were comprised of multiple variants. Pneumonia severity did not vary by subgroup (p = 0.264). In both the F and G gene, the sequenced regions were found to be predominantly under purifying selection.

CONCLUSION

Subgroup patterns from this rural African setting temporally map with global strain distribution, suggesting a well-mixed global virus transmission pool of HMPV. Persistence in the local community is characterized by repeated introductions of HMPV variants from the global pool. The factors underlying the declining prevalence of HMPV in this population should be investigated.

Rapid diagnosis of human adenovirus B, C and E in the respiratory tract using multiplex quantitative polymerase chain reaction

Human adenovirus (HAdV) is increasingly recognized as a major cause of human respiratory tract viral infections. Its outbreaks and epidemics in various populations resulted in considerable morbidity and mortality. Therefore, a rapid and specific assay for HAdV in clinical samples is of crucial importance to diagnosing HAdV infections. The present study aimed to develop and evaluate a multiplex quantitative polymerase chain reaction (qPCR) assay for the rapid detection and accurate quantification of HAdV B, C and E. The lower limit of detection for this assay was two genomic copies per reaction, and quantitative linearity ranged from 2 to 2×10⁶ copies per reaction of the input viral DNA. Furthermore, 3,160 throat swab samples that tested HAdV negative by the immunofluorescence assay were collected and retested using the multiplex qPCR assay. The results showed that 2,906 samples were HAdV negative and the other 254 samples were HAdV positive. The HAdV species identified included B (184 samples), C (51 samples), and E (39 samples). Among the three HAdV species, HAdV B and E were detected from 8 samples, and HAdV C and E were detected from other 12 samples. The overall results demonstrated that the sensitivity and specificity of the proposed assay were 100% (254/254) and 99.6% (2894/2906), respectively. From the perspective of routine clinical diagnosis, this assay represented a rapid (≤1.5 h) and economic strategy, and had the potential to be used for the rapid and accurate diagnosis of human respiratory infections caused by HAdV B, C and E.

Virus detection by PCR following vaccination of naive calves with intranasal or injectable multivalent modified-live viral vaccines

We evaluated duration of PCR-positive results following administration of modified-live viral (MLV) vaccines to beef calves. Twenty beef calves were randomly assigned to either group 1 and vaccinated intranasally with a MLV vaccine containing bovine alphaherpesvirus 1 (BoHV-1), bovine respiratory syncytial virus (BRSV), and bovine parainfluenza virus 3 (BPIV-3), or to group 2 and vaccinated subcutaneously with a MLV vaccine containing bovine viral diarrhea virus 1 and 2 (BVDV-1, -2), BoHV-1, BRSV, and BPIV-3. Deep nasopharyngeal swabs (NPS) and transtracheal washes (TTW) were collected from all calves, and whole blood was collected from group 2 calves and tested by PCR. In group 1, the proportions of calves that tested PCR-positive to BVDV, BoHV-1, BRSV, and BPIV-3 on any sample at any time were 0%, 100%, 100%, and 10%, respectively. In group 1 calves, 100% of calves became PCR-positive for BoHV-1 by day 3 post-vaccination and 100% of calves became PCR-positive for BRSV by day 7 post-vaccination. In group 2, the proportions of calves that tested positive to BVDV, BoHV-1, BRSV, and BPIV-3 on any sample at any time were 50%, 40%, 10%, and 0%, respectively. All threshold cycle (Ct) values were >30 in group 2 calves, irrespective of virus; however, Ct values <25 were observed in group 1 calves from PCR-positive results for BoHV-1 and BRSV. All calves were PCR-negative for all viruses after day 28. Following intranasal MLV viral vaccination, PCR results and Ct values for BRSV and BoHV-1 suggest that attempts to differentiate vaccine virus from natural infection is unreliable.

Recent sequence variation in probe binding site affected detection of respiratory syncytial virus group B by real-time RT-PCR

BACKGROUND

Direct immuno-fluorescence test (IFAT) and multiplex real-time RT-PCR have been central to RSV diagnosis in Kilifi, Kenya. Recently, these two methods showed discrepancies with an increasing number of PCR undetectable RSV-B viruses.

OBJECTIVES

Establish if mismatches in the primer and probe binding sites could have reduced real-time RT-PCR sensitivity.

STUDY DESIGN

Nucleoprotein (N) and glycoprotein (G) genes were sequenced for real-time RT-PCR positive and negative samples. Primer and probe binding regions in N gene were checked for mismatches and phylogenetic analyses done to determine molecular epidemiology of these viruses. New primers and probe were designed and tested on the previously real-time RT-PCR negative samples.

RESULTS

N gene sequences revealed 3 different mismatches in the probe target site of PCR negative, IFAT positive viruses. The primers target sites had no mismatches. Phylogenetic analysis of N and G genes showed that real-time RT-PCR positive and negative samples fell into distinct clades. Newly designed primers-probe pair improved detection and recovered previous PCR undetectable viruses.

CONCLUSIONS

An emerging RSV-B variant is undetectable by a quite widely used real-time RT-PCR assay due to polymorphisms that influence probe hybridization affecting PCR accuracy.

Ten years of R&D and full automation in molecular diagnosis

A 10-year experience of our automated molecular diagnostic platform that carries out 91 different real-time PCR is described. Progresses and future perspectives in molecular diagnostic microbiology are reviewed: why automation is important; how our platform was implemented; how homemade PCRs were developed; the advantages/disadvantages of homemade PCRs, including the critical aspects of troubleshooting and the need to further reduce the turnaround time for specific samples, at least for defined clinical settings such as emergencies. The future of molecular diagnosis depends on automation, and in a novel perspective, it is time now to fully acknowledge the true contribution of molecular diagnostic and to reconsider the indication for PCR, by also using these tests as first-line assays.

Quantification of Hepatitis E Virus in Naturally-Contaminated Pig Liver Products

Hepatitis E virus (HEV), the cause of self-limiting acute hepatitis in humans, is widespread and endemic in many parts of the world. The foodborne transmission of HEV has become of concern due to the identification of undercooked pork products as a risk factor for infection. Foodborne enteric viruses are conventionally processed by quantitative RT-PCR (RT-qPCR), which gives sensitive and quantitative detection results. Recently, digital PCR (dPCR) has been described as a novel approach to genome quantification with no need for a standard curve. The performance of microfluidic digital RT-PCR (RT-dPCR) was compared to RT-qPCR when detecting HEV in pig liver products. The sensitivity of the RT-dPCR assay was similar to that of RT-qPCR, and quantitative data obtained by both detection methods were not significantly different for almost all samples. This absolute quantification approach may be useful for standardizing quantification of HEV in food samples and may be extended to quantifying other human pathogens in food samples.

A novel multiplex RT-qPCR method based on dual-labelled probes suitable for typing all known genotypes of viral haemorrhagic septicaemia virus

Viral haemorrhagic septicaemia (VHS) is a notifiable fish disease, whose causative agent is a rhabdovirus isolated from a wide range of fish species, not only in fresh but also in marine and brackish waters. Phylogenetic studies have identified four major genotypes, with a strong geographical relationship. In this study, we have designed and validated a new procedure--named binary multiplex RT-qPCR (bmRT-qPCR)--for simultaneous detection and typing of all four genotypes of VHSV by real-time RT-PCR based on dual-labelled probes and composed by two multiplex systems designed for European and American/Asiatic isolates, respectively, using a combination of three different fluorophores. The specificity of the procedure was assessed by including a panel of 81 VHSV isolates covering all known genotypes and subtypes of the virus, and tissue material from experimentally infected rainbow trout, resulting in a correct detection and typing of all strains. The analytical sensitivity was evaluated in a comparative assay with titration in cell culture, observing that both methods provided similar limits of detection. The proposed method can be a powerful tool for epidemiological analysis of VHSV by genotyping unknown samples within a few hours.

Design of primers and probes for quantitative real-time PCR methods

Design of primers and probes is one of the most crucial factors affecting the success and quality of quantitative real-time PCR (qPCR) analyses, since an accurate and reliable quantification depends on using efficient primers and probes. Design of primers and probes should meet several criteria to find potential primers and probes for specific qPCR assays. The formation of primer-dimers and other non-specific products should be avoided or reduced. This factor is especially important when designing primers for SYBR(®) Green protocols but also in designing probes to ensure specificity of the developed qPCR protocol. To design primers and probes for qPCR, multiple software programs and websites are available being numerous of them free. These tools often consider the default requirements for primers and probes, although new research advances in primer and probe design should be progressively added to different algorithm programs. After a proper design, a precise validation of the primers and probes is necessary. Specific consideration should be taken into account when designing primers and probes for multiplex qPCR and reverse transcription qPCR (RT-qPCR). This chapter provides guidelines for the design of suitable primers and probes and their subsequent validation through the development of singlex qPCR, multiplex qPCR, and RT-qPCR protocols.

Development and deployment of a rapid recombinase polymerase amplification Ebola virus detection assay in Guinea in 2015

In the absence of a vaccine or specific treatments for Ebola virus disease (EVD), early identification of cases is crucial for the control of EVD epidemics. We evaluated a new extraction kit (SpeedXtract (SE), Qiagen) on sera and swabs in combination with an improved diagnostic reverse transcription recombinase polymerase amplification assay for the detection of Ebola virus (EBOV-RT-RPA). The performance of combined extraction and detection was best for swabs. Sensitivity and specificity of the combined SE and EBOV-RT-RPA were tested in a mobile laboratory consisting of a mobile glovebox and a Diagnostics-in-a-Suitcase powered by a battery and solar panel, deployed to Matoto Conakry, Guinea as part of the reinforced surveillance strategy in April 2015 to reach the goal of zero cases. The EBOV-RT-RPA was evaluated in comparison to two real-time PCR assays. Of 928 post-mortem swabs, 120 tested positive, and the combined SE and EBOV-RT-RPA yielded a sensitivity and specificity of 100% in reference to one real-time RT-PCR assay. Another widely used real-time RT-PCR was much less sensitive than expected. Results were provided very fast within 30 to 60 min, and the field deployment of the mobile laboratory helped improve burial management and community engagement.

Molecular confirmation of infectious spleen and kidney necrosis virus (ISKNV) in farmed and imported ornamental fish in Australia

Viruses of the genus Megalocytivirus have not been detected in wild populations of fish in Australia but circulate in imported ornamental fish. In 2012, detection of a megalocytivirus in healthy platys Xiphophorus maculatus was reported from a farm in Australia during surveillance testing as part of a research project undertaken at the University of Sydney. Confirmatory testing of the original samples at the AAHL Fish Diseases Laboratory verified the presence of an infectious spleen and kidney necrosis virus (ISKNV)-like virus. Additional sampling at the positive farm confirmed the persistence of the virus in the platys, with 39 of 265 (14.7%) samples testing positive. Comparison of 3 separate gene regions of the virus with those of ISKNV confirmed the detection of a virus indistinguishable from ISKNV. Subsequently, ISKNV was also detected in a range of imported ornamental fish from several countries between 2013 and 2014, by screening with real-time PCR and confirmation by conventional PCR and sequence analysis. Accordingly, the current importation of live ornamental fish acts as a potential perpetual source for the establishment of ISKNV viruses within Australia. The testing of the farmed and imported ornamental fish verified the utility of the probe-based real-time PCR assay for screening of ornamental fish for Megalocytivirus.

"ISA-Lation" of Single-Stranded Positive-Sense RNA Viruses from Non-Infectious Clinical/Animal Samples

Isolation of viral pathogens from clinical and/or animal samples has traditionally relied on either cell cultures or laboratory animal model systems. However, virus viability is notoriously susceptible to adverse conditions that may include inappropriate procedures for sample collection, storage temperature, support media and transportation. Using our recently described ISA method, we have developed a novel procedure to isolate infectious single-stranded positive-sense RNA viruses from clinical or animal samples. This approach, that we have now called "ISA-lation", exploits the capacity of viral cDNA subgenomic fragments to re-assemble and produce infectious viral RNA in susceptible cells. Here, it was successfully used to rescue enterovirus, Chikungunya and Tick-borne encephalitis viruses from a variety of inactivated animal and human samples. ISA-lation represents an effective option to rescue infectious virus from clinical and/or animal samples that may have deteriorated during the collection and storage period, but also potentially overcomes logistic and administrative difficulties generated when complying with current health and safety and biosecurity guidelines associated with shipment of infectious viral material.

Analysis of Coinfections with A/H1N1 Strain Variants among Pigs in Poland by Multitemperature Single-Strand Conformational Polymorphism

Monitoring and control of infections are key parts of surveillance systems and epidemiological risk prevention. In the case of influenza A viruses (IAVs), which show high variability, a wide range of hosts, and a potential of reassortment between different strains, it is essential to study not only people, but also animals living in the immediate surroundings. If understated, the animals might become a source of newly formed infectious strains with a pandemic potential. Special attention should be focused on pigs, because of the receptors specific for virus strains originating from different species, localized in their respiratory tract. Pigs are prone to mixed infections and may constitute a reservoir of potentially dangerous IAV strains resulting from genetic reassortment. It has been reported that a quadruple reassortant, A(H1N1)pdm09, can be easily transmitted from humans to pigs and serve as a donor of genetic segments for new strains capable of infecting humans. Therefore, it is highly desirable to develop a simple, cost-effective, and rapid method for evaluation of IAV genetic variability. We describe a method based on multitemperature single-strand conformational polymorphism (MSSCP), using a fragment of the hemagglutinin (HA) gene, for detection of coinfections and differentiation of genetic variants of the virus, difficult to identify by conventional diagnostic.

Simultaneous detection of five notifiable viral diseases of cattle by single-tube multiplex real-time RT-PCR

Multiplexed real-time PCR (qPCR) assays enable the detection of several target genes in a single reaction, which is applicable for simultaneous testing for the most important viral diseases in samples obtained from ruminants with unspecific clinical symptoms. Here, reverse transcription qPCR (RT-qPCR) systems for the detection of bovine viral diarrhoea virus (BVDV) and bluetongue virus (BTV) were combined with an internal control system based on the beta-actin gene. Additionally, a background screening for three further major pathogens of cloven-hoofed animals reportable to the World Organisation for Animal Health, namely foot-and-mouth disease virus, epizootic haemorrhagic disease virus, and Rift Valley fever virus, was integrated using the identical fluorophore for the respective RT-qPCR assays. Every pathogen-specific assay had an analytical sensitivity of at least 100 genome copies per reaction within the multiplex approach, and a series of reference samples and clinical specimens obtained from cattle, but also from small ruminants, were detected reliably. The qPCR systems integrated in the background screening were even not influenced by the simultaneous amplification of very high BVDV and BTV genome copy numbers. The newly developed multiplex qPCR allows the specific and sensitive detection of five of the most important diseases of ruminants and could be used in the context of monitoring programs or for differential diagnostics.

Single-channel multiplexing without melting curve analysis in real-time PCR

Multiplex real-time PCR with quantification of targets in a single fluorescence channel has been the demand in biotechnology industry. Here, we develop a novel analytical real-time PCR technique to detect multiple targets in a single fluorescence channel without melting curve analysis. In this technique, we show the intensity of the fluorescence signals of two discrete Tm targets is different at certain temperatures called detection temperatures, by which a high Tm target can be detected regardless of a low Tm target. We then identify the low Tm target by utilizing a change of the fluorescence signals between two different detection temperatures. Furthermore, it enables us to determine quantification of each target in a single channel, possibly facilitating convenient patient care for drug treatment in clinics.

Use of molecular assays for the diagnosis of influenza

Respiratory infections are the third highest cause of death worldwide and influenza has the highest mortality rate among lower respiratory tract infections (LRTIs). Diagnosis of LRTIs relies mostly on clinical symptoms and is not fully satisfactory. Influenza laboratory diagnosis improves the efficiency of prophylaxis or treatment of influenza by antiviral molecules and has a strong impact on the cost-effectiveness of curative treatment. Inappropriate treatment of patients may result in spreading of resistant strains. Molecular diagnostics play a central role in the surveillance and response of pandemic influenza due to highly pathogenic strains. Real-time assays can be used for diagnosis or surveillance purposes in humans and animals, and microarrays can be used to identify and monitor the spread of dangerous variants. Molecular assays are also useful to identify and distinguish influenza, other respiratory viruses and bacteria, although their cost-effectiveness must be proven on a large scale. As new antiviral options will be available to clinicians, a better treatment choice will benefit the patient and community. Recent progress in molecular techniques will be reviewed. Examples of real-time assays for the detection of influenza viruses, including the highly pathogenic influenza A strains H5N1 and H7N7, will be discussed. Promising new techniques that allow detailed genotyping of viruses or multiplex detection of several respiratory pathogens from a unique specimen will also be discussed. These techniques will, in the near future, significantly improve the quality of diagnosis and surveillance of respiratory pathogens.

The use of dried cerebrospinal fluid filter paper spots as a substrate for PCR diagnosis of the aetiology of bacterial meningitis in the Lao PDR

We investigated whether dried cerebrospinal fluid (CSF) conserved on filter paper can be used as a substrate for accurate PCR diagnosis of important causes of bacterial meningitis in the Lao PDR. Using mock CSF, we investigated and optimized filter paper varieties, paper punch sizes, elution volumes and quantities of DNA template to achieve sensitive and reliable detection of bacterial DNA from filter paper specimens. FTA Elute Micro Card™ (Whatman, Maidstone, UK) was the most sensitive, consistent and practical variety of filter paper. Following optimization, the lower limit of detection for Streptococcus pneumoniae from dried mock CSF spots was 14 genomic equivalents (GE)/μL (interquartile range 5.5 GE/μL) or 230 (IQR 65) colony forming units/mL. A prospective clinical evaluation for S. pneumoniae, S. suis and Neisseria meningitidis was performed. Culture and PCR performed on fresh liquid CSF from patients admitted with a clinical diagnosis of meningitis (n = 73) were compared with results derived from dried CSF spots. Four of five fresh PCR-positive CSF samples also tested PCR positive from dried CSF spots, with one patient under the limit of detection. In a retrospective study of S. pneumoniae samples (n = 20), the median (IQR; range) CSF S. pneumoniae bacterial load was 1.1 × 10(4) GE/μL (1.2 × 10(5) ; 1 to 6.1 × 10(6) DNA GE/μL). Utilizing the optimized methodology, we estimate an extrapolated sensitivity of 90%, based on the range of CSF genome counts found in Laos. Dried CSF filter paper spots could potentially help us to better understand the epidemiology of bacterial meningitis in resource-poor settings and guide empirical treatments and vaccination policies.

Development of a primer-probe energy transfer based real-time PCR for the detection of Swine influenza virus

Swine influenza virus (SIV) causes a contagious and requiring official notification disease of pigs and humans. In this study, a real-time reverse transcription-polymerase chain reaction (RT-PCR) assay based on primer-probe energy transfer (PriProET) for the detection of SIV RNA was developed. The assay uses matrix gene-specific primers and an Oregon Green-labeled fluorescent probe and was employed for the detection of SIV in clinical samples to identify outbreaks and to monitor the prevalence of disease. The PriProET technology was used to obtain a probe melting profile for confirmation of the specific product amplification. The assay is specific for influenza virus with a sensitivity of detection limit of approximately 10 copies of RNA by PCR. Based on serial dilutions of SIV, the detection limit of the assay was approximately 0.003 TCID(50)/ml for H1N1 A/Swine/Poland/KPR9/2004 virus. The PriProET RT-PCR was suitable for the detection of SIV RNA isolated directly from clinical samples. The assay detected SIV RNA in pre-clinical swab samples as early as 2 days post-infection (dpi). The PriProET RT-PCR assay is an alternative to the existing diagnostic assays and could have enhanced applicability for clinical diagnosis.

Development of a panel of recombinase polymerase amplification assays for detection of biothreat agents

Syndromic panels for infectious disease have been suggested to be of value in point-of-care diagnostics for developing countries and for biodefense. To test the performance of isothermal recombinase polymerase amplification (RPA) assays, we developed a panel of 10 RPAs for biothreat agents. The panel included RPAs for Francisella tularensis, Yersinia pestis, Bacillus anthracis, variola virus, and reverse transcriptase RPA (RT-RPA) assays for Rift Valley fever virus, Ebola virus, Sudan virus, and Marburg virus. Their analytical sensitivities ranged from 16 to 21 molecules detected (probit analysis) for the majority of RPA and RT-RPA assays. A magnetic bead-based total nucleic acid extraction method was combined with the RPAs and tested using inactivated whole organisms spiked into plasma. The RPA showed comparable sensitivities to real-time RCR assays in these extracts. The run times of the assays at 42°C ranged from 6 to 10 min, and they showed no cross-detection of any of the target genomes of the panel nor of the human genome. The RPAs therefore seem suitable for the implementation of syndromic panels onto microfluidic platforms.

Laboratory detection of respiratory viruses by automated techniques

Advances in clinical virology for detecting respiratory viruses have been focused on nucleic acids amplification techniques, which have converted in the reference method for the diagnosis of acute respiratory infections of viral aetiology. Improvements of current commercial molecular assays to reduce hands-on-time rely on two strategies, a stepwise automation (semi-automation) and the complete automation of the whole procedure. Contributions to the former strategy have been the use of automated nucleic acids extractors, multiplex PCR, real-time PCR and/or DNA arrays for detection of amplicons. Commercial fully-automated molecular systems are now available for the detection of respiratory viruses. Some of them could convert in point-of-care methods substituting antigen tests for detection of respiratory syncytial virus and influenza A and B viruses. This article describes laboratory methods for detection of respiratory viruses. A cost-effective and rational diagnostic algorithm is proposed, considering technical aspects of the available assays, infrastructure possibilities of each laboratory and clinic-epidemiologic factors of the infection.

Early HHV-6 replication is associated with morbidity non-related to CMV infection after kidney transplantation

Human herpesvirus type 6-(HHV-6) has been associated with morbidity after liver transplantation.

OBJECTIVE

The aim of this study was to determine the HHV-6 seroprevalence among donor-recipient pairs, analyze the incidence of early active infection, its clinical manifestation, interaction with CMV, and the related morbidity in the first year after kidney transplantation.

METHODS

46 donor-recipient pairs had IgG evaluated by ELISA before transplantation: HHV-6(Pambio - USA) and CMV-(Roche - USA). A frozen whole blood sample collected weekly (from the 1st to the 6th week) was retrospectively tested for HHV-6 viral load (VL) determination by real time quantitative PCR (qPCR, Nanogen - Italy). Patients were preemptively surveyed for CMV by pp65 antigenemia (Ag, APAAP, immunohistochemistry, Biotest - Germany) from the 4th to the 12th week after transplantation. Active infection was defined as qPCR-HHV6+ (viral-load/mL-VL) and Ag+ (+cells/100.000 granulocytes), for HHV-6 and CMV, respectively. DCMV was defined as simultaneous positive antigenemia and suggestive signs/symptoms. Concerning +qPCR-HHV6, associated factors, clinical manifestation, interaction with CMV and morbidity were searched.

RESULTS

Pre-transplant HHV-6 seroprevalence was significantly higher among kidney recipients compared to their donors (82.6x54.8%; p = 0.005 [3.9 (1.4-10.4)]). Active infection by this virus occurred in 26.1% (12/46), with no association with previous IgG (p = 0.412). Median VL was 125 copies/mL (53-11.264), and the median Ag was 21 +cells (2-740). There was no association between HHV-6 and CMV activation after transplantation (p = 0.441), neither concerning DCMV (p = 0.596). Median highest Ag+ and days of ganciclovir treatment were similar between qPCR-HHV6 + or - (p = 0.206 and p = 0.124, respectively). qPCR-HHV6+ was associated with higher incidence of bacterial (p = 0.009) and fungal (p = 0.001) infections, and higher number (p = 0.001) of hospital admission and longer duration of hospitalization over the first 6 and 12 months post-transplantation (p = 0.033 and p = 0.001).

CONCLUSION

Latent HHV-6 infection is more common among recipients than donors before transplantation. Early active infection by this pathogen after transplantation does not increase DCMV incidence or severity during the first 3 months of follow-up. However, early HHV-6 replication is associated with other infections and hospitalizations in the first year.

One-step multiplex real time RT-PCR for the detection of bovine respiratory syncytial virus, bovine herpesvirus 1 and bovine parainfluenza virus 3

Background

Detection of respiratory viruses in veterinary species has traditionally relied on virus detection by isolation or immunofluorescence and/or detection of circulating antibody using ELISA or serum neutralising antibody tests. Multiplex real time PCR is increasingly used to diagnose respiratory viruses in humans and has proved to be superior to traditional methods. Bovine respiratory disease (BRD) is one of the most common causes of morbidity and mortality in housed cattle and virus infections can play a major role. We describe here a one step multiplex reverse transcriptase quantitative polymerase chain reaction (mRT-qPCR) to detect the viruses commonly implicated in BRD.

Results

A mRT-qPCR assay was developed and optimised for the simultaneous detection of bovine respiratory syncytial virus (BRSV), bovine herpes virus type 1 (BoHV-1) and bovine parainfluenza virus type 3 (BPI3 i & ii) nucleic acids in clinical samples from cattle. The assay targets the highly conserved glycoprotein B gene of BoHV-1, nucleocapsid gene of BRSV and nucleoprotein gene of BPI3. This mRT-qPCR assay was assessed for sensitivity, specificity and repeatability using in vitro transcribed RNA and recent field isolates. For clinical validation, 541 samples from clinically affected animals were tested and mRT-qPCR result compared to those obtained by conventional testing using virus isolation (VI) and/or indirect fluorescent antibody test (IFAT).

Conclusions

The mRT-qPCR assay was rapid, highly repeatable, specific and had a sensitivity of 97% in detecting 10² copies of BRSV, BoHV-1 and BPI3 i & ii. This is the first mRT-qPCR developed to detect the three primary viral agents of BRD and the first multiplex designed using locked nucleic acid (LNA), minor groove binding (MGB) and TaqMan probes in one reaction mix. This test was more sensitive than both VI and IFAT and can replace the aforesaid methods for virus detection during outbreaks of BRD.

Standardized one-step real-time reverse transcription-PCR assay for universal detection and quantification of hepatitis delta virus from clinical samples in the presence of a heterologous internal-control RNA

As for other chronic viral diseases, quantification of hepatitis delta virus (HDV) loads may be useful for patient management. We describe a one-step quantitative reverse transcription-PCR assay that is reliable and automatable and meets the regulatory authorities' standards for accurate quantification of the major HDV genotypes. It includes an internal control and uses in vitro-transcribed RNAs as standards. Its linearity range is 500 to 1.7 × 10(11) copies/ml, its sensitivity is around 150 copies/ml, its repeatability is around 15%, and its reproducibility is below 0.25 log(10) copies/ml.

Respiratory viruses involved in influenza-like illness in a Greek pediatric population during the winter period of the years 2005-2008

Viruses are the major cause of pediatric respiratory tract infection and yet many suspected cases of illness remain uncharacterized. This study aimed to determine the distribution of several respiratory viruses in children diagnosed as having influenza‐like illness, over the winter period of 2005–2008. Molecular assays including conventional and real time PCR protocols, were employed to screen respiratory specimens, collected by clinicians of the Influenza sentinel system and of outpatient pediatric clinics, for identification of several respiratory viruses. Of 1,272 specimens tested, 814 (64%) were positive for at least one virus and included 387 influenza viruses, 160 rhinoviruses, 155 respiratory syncytial viruses, 95 adenoviruses, 81 bocaviruses, 47 parainfluenza viruses, 44 metapneumoviruses, and 30 coronaviruses. Simultaneous presence of two or three viruses was observed in 173 of the above positive cases, 21% of which included influenza virus and rhinovirus. The majority of positive cases occurred during January and February. Influenza virus predominated in children older than 1 year old, with type B being the dominant type for the first season and subtypes A/H3N2 and A/H1N1 the following two winter seasons, respectively. Respiratory syncytial virus prevailed in children younger than 2 years old, with subtypes A and B alternating from year to year. This is the most comprehensive study of the epidemiology of respiratory viruses in Greece, indicating influenza, rhinovirus and respiratory syncytial virus as major contributors to influenza‐like illness in children. J. Med. Virol. 83:1841–1848, 2011. © 2011 Wiley‐Liss, Inc.

Multiplex detection and SNP genotyping in a single fluorescence channel

Probe-based PCR is widely used for SNP (single nucleotide polymorphism) genotyping and pathogen nucleic acid detection due to its simplicity, sensitivity and cost-effectiveness. However, the multiplex capability of hydrolysis probe-based PCR is normally limited to one target (pathogen or allele) per fluorescence channel. Current fluorescence PCR machines typically have 4–6 channels. We present a strategy permitting the multiplex detection of multiple targets in a single detection channel. The technique is named Multiplex Probe Amplification (MPA). Polymorphisms of the CYP2C9 gene (cytochrome P450, family 2, subfamily C, polypeptide 9, CYP2C9*2) and human papillomavirus sequences HPV16, 18, 31, 52 and 59 were chosen as model targets for testing MPA. The allele status of the CYP2C9*2 determined by MPA was entirely concordant with the reference TaqMan® SNP Genotyping Assays. The four HPV strain sequences could be independently detected in a single fluorescence detection channel. The results validate the multiplex capacity, the simplicity and accuracy of MPA for SNP genotyping and multiplex detection using different probes labeled with the same fluorophore. The technique offers a new way to multiplex in a single detection channel of a closed-tube PCR.

Rapid and Real-time Detection of Human Viral Infections: Current Trends and Future Perspectives

The development of technologies with rapid and sensitive detection capabilities and increased throughput have become crucial for responding to greater number of threats posed by emerging and re-emerging viruses in the recent past. The conventional identification methods require time-consuming culturing, and/or detection of antibodies, which are not very sensitive and specific. The recent advances in molecular biology techniques in the field of genomics and proteomics greatly facilitate the rapid identification with more accuracy. The real-time assays viz; SYBR green I based real time RT-PCR and RT-LAMP have been developed for rapid detection as well as typing of some of the emerging arboviruses of biomedical importance viz; Dengue, Japanese Encephalitis, Chikungunya, West Nile, SARS and Swine Flu etc. Both these techniques are capable of detection and differentiation as well as quantifying viral load with higher sensitivity, rapidity and specificity. One of the most important advantages of RT-LAMP is its field applicability, without requirement of any sophisticated equipments. The establishment of these real time molecular assays will certainly facilitate the rapid detection of viruses with high degree of precision and accuracy in future.

An appraisal of PCR-based technology in the detection of Mycobacterium tuberculosis

Tuberculosis is an under-recognized yet catastrophic health problem, particularly in developing countries. The HIV pandemic has served to increase the number of susceptible individuals, and multidrug-resistance and poor socioeconomic conditions also augment the prevalence and the consequences of the disease. To control the disease and its spread, it is vital that tuberculosis diagnostics are accurate and rapid. Whereas microscopy and culture have several limitations (low sensitivity is a problem for the former, while the latter has a delayed turnaround time), PCR-based techniques targeting regions of the Mycobacterium tuberculosis genome such as IS6110 have proved to be useful. The purpose of this review is to assess the use of PCR-RFLP, nested PCR and real-time PCR protocols and the choice of target regions for the detection of M. tuberculosis. Real-time PCR for the detection of M. tuberculosis target genes in clinical specimens has contributed to improving diagnosis and epidemiologic surveillance in the past decade. However, targeting one genome sequence such as IS6110 may not by itself be sufficiently sensitive to reach 100% diagnosis, especially in the case of pulmonary tuberculosis. Additional testing for target genome sequences such as hsp65 seems encouraging. An interesting approach would be a multiplex real-time PCR targeting both IS6110 and hsp65 to achieve comprehensive and specific molecular diagnosis. This technology needs development and adequate field testing before it becomes the acceptable gold standard for diagnosis.

Comparison of a conventional polymerase chain reaction with real-time polymerase chain reaction for the detection of neurotropic viruses in cerebrospinal fluid samples

PURPOSE

To compare a conventional polymerase chain reaction (PCR) and real-time PCR for the detection of neurotropic DNA viruses.

MATERIALS AND METHODS

A total of 147 cerebrospinal fluid (CSF) samples was collected from patients attending a tertiary care hospital in South India for a period from 2005 to 2008. All these samples were tested using a conventional multiplex/uniplex PCR and a real-time multiplex/uniplex PCR. This technique was used to detect a large number of herpes viruses responsible for central nervous system infections, including HSV-1, HSV-2, VZV, CMV and EBV and the polyoma virus JCV.

RESULTS

Overall, in the entire set of samples, the real-time PCR yielded 88 (59.9%) positives and conventional PCR had six (4.1%) positives.

CONCLUSION

Our results suggest that the real-time PCR assay was more sensitive compared with the conventional PCR. The advantage of real-time PCR is that it can be performed much faster than conventional PCR. Real-time PCR is less time-consuming, less labour-intensive and also reduces the chance of contamination as there is no post-amplification procedure. In the entire study population, the major viruses detected using real-time PCR were EBV (34%), HSV-2 (10.8%) and VZV (6.8%).

Quantitative polymerase chain reaction (PCR) for detection of aquatic animal pathogens in a diagnostic laboratory setting

Real-time, or quantitative, polymerase chain reaction (qPCR) is quickly supplanting other molecular methods for detecting the nucleic acids of human and other animal pathogens owing to the speed and robustness of the technology. As the aquatic animal health community moves toward implementing national diagnostic testing schemes, it will need to evaluate how qPCR technology should be employed. This review outlines the basic principles of qPCR technology, considerations for assay development, standards and controls, assay performance, diagnostic validation, implementation in the diagnostic laboratory, and quality assurance and control measures. These factors are fundamental for ensuring the validity of qPCR assay results obtained in the diagnostic laboratory setting.

One-step RT-qPCR with an internal control system for the detection of turkey rotaviruses in faecal samples

Turkey rotaviruses are one of the major pathogens responsible for the poult enteritis syndrome (PES). In this study a one step real-time reverse transcription polymerase chain reaction (RT-qPCR) assay targeting the rotaviral non-structural protein 4 (NSP4) was developed. The NSP4 is a highly conserved gene inside the turkey rotavirus genome and contains an internal control system to monitor any potential RT-qPCR inhibitors. The detection limit of the optimized NSP4-RT-qPCR assay ranged from 8.15 to 8.15 × 10(5) copy numbers. In total 149 faecal samples were collected from eight different flocks of commercial turkey farms. Faecal samples from hens and toms were collected separately at 2-week intervals from the 2nd week of age through the 16th and 20th week of age (age of slaughter for female and male, respectively) and tested. One farm reared only hens. The samples were tested previously using conventional RT-PCR targeting the same gene. When the conventional RT-PCR was compared with the developed NSP4-RT-qPCR, the results revealed that 11% of the samples of the conventional RT-PCR were false negative. The results indicate that this NSP4-RT-qPCR is highly sensitive for the detection of turkey rotaviruses in faeces. In addition, it could be suitable for the development of high-throughput screening.

Rapid simultaneous detection of enterovirus and parechovirus RNAs in clinical samples by one-step real-time reverse transcription-PCR assay

Enteroviruses (EVs) are recognized as the major etiological agent in meningitis in children and young adults. The use of molecular techniques, such as PCR, has substantially improved the sensitivity of enterovirus detection compared to that of virus culture methods. PCR-based methods also can detect a much wider range of EV variants, including those within species A, as well as human parechoviruses (HPeVs) that often grow poorly in vitro and which previously have been underdiagnosed by traditional methods. To exploit these developments, we developed a real-time one-step reverse transcription-PCR (RT-PCR) for the rapid and sensitive detection of EV and HPeV in clinical specimens. Two commercially available RT-PCR kits were used (method I, Platinum one-step kit; method II, Express qPCR one-step kit) with primers and probes targeting the EV and HPeV 5'-untranslated regions (5'UTR). Amplification dynamics (threshold cycle [C(T)]values and efficiencies) of absolutely quantified full-length RNA transcripts representative of EV species A to D and HPeV were similar, demonstrating the effectiveness of both assays across the range of currently described human EV and HPeV variants. Probit analysis of multiple endpoint replicates demonstrated comparable sensitivities of the assays for EV and HPeV (method I, approximately 10 copies per reaction for both targets; method II, 20 copies per reaction). C(T) values were highly reproducible on repeat testing of positive controls within assays and between assay runs. Considering the sample turnaround time of less than 3 h, the multiplexed one-step RT-PCR method provides rapid diagnostic testing for EV and HPeV in cases of suspected central nervous system infections in a clinically relevant time frame.

Detection and differentiation of bovine herpesvirus 1 and 5 using a multiplex real-time polymerase chain reaction

A multiplex real-time PCR was developed for the detection and differentiation of two closely related bovine herpesviruses 1 (BoHV-1) and 5 (BoHV-5). The multiplex real-time PCR combines a duplex real-time PCR that targets the DNA polymerase gene of BoHV-1 and BoHV-5 and a real-time PCR targeting mitochondrial DNA, as a house-keeping gene, described previously by Cawthraw et al. (2009). The assay correctly identified 22 BoHV-1 and six BoHV-5 isolates from the Biosecurity Sciences Laboratory virus collection. BoHV-1 and BoHV-5 were also correctly identified when incorporated in spiked semen and brain tissue samples. The detection limits of the duplex assay were 10 copies of BoHV-1 and 45 copies of BoHV-5. The multiplex real-time PCR had reaction efficiencies of 1.04 for BoHV-1 and 1.08 for BoHV-5. Standard curves relating Ct value to template copy number had correlation coefficients of 0.989 for BoHV-1 and 0.978 for BoHV-5. The assay specificity was demonstrated by testing bacterial and viral DNA from pathogens commonly isolated from bovine respiratory and reproductive tracts. The validated multiplex real-time PCR was used to detect and differentiate BoHV-1 and BoHV-5 in bovine clinical samples with known histories.

Reevaluating and optimizing polyomavirus BK and JC real-time PCR assays to detect rare sequence polymorphisms

PCR-based molecular assays have a central role in polyomavirus diagnostics. To assure optimal performance, target sequences should be regularly updated according to newly available sequences. The aim of this study was to review our in-house polyomavirus BK (BKV) and JC (JCV) real-time PCR assays. Database analysis revealed variations in the BKV target region which might affect the assay performance, while no significant changes were found in the JCV target region. We compared two degenerate versions of our BKV primers which accommodated at least 95% of all published genetic variants. Dilutions of cloned viral genomic DNA and probit analysis indicated an analytical sensitivity of the updated BKV assay of 4.15 copies/reaction and that of the JCV assay was 3.37 copies/reaction. The specificity was assessed by testing JCV- and BKV-positive samples that showed no cross-reactivity. The performance of the original and updated BKV assay was compared in 101 urine and 200 plasma samples submitted to our routine diagnostic laboratory revealed similar quantitative results. We conclude that our JCV and updated BKV real-time PCR assays are robust and detect rare variants possibly encountered in the clinical routine.

TaqMan real-time reverse transcription-PCR assay for universal detection and quantification of avian hepatitis E virus from clinical samples in the presence of a heterologous internal control RNA

Avian hepatitis E virus (HEV) isolates could be separated into at least three genotypes. In this study, the development of the first duplex TaqMan real-time reverse transcription-PCR (RT-PCR) assay for detection and quantification of avian HEV is presented. Primers and probes binding within relatively conserved open reading frame 3 (ORF3) were designed. Tenfold dilution series of in vitro-transcribed avian HEV RNA were used as the standard for quantification. A 712-bp region of the green fluorescent protein gene was transcribed in vitro and used as a heterologous internal control for both RNA isolation and real-time RT-PCR. The duplex real-time RT-PCR for avian HEV had an efficiency of 1.04, a regression squared value of 0.996, and a sensitivity of approximately 3.6 × 10(3) copies per reaction mixture when in vitro-transcribed RNA was used as the template. The presence of in vitro-transcribed heterologous internal control RNA did not affect amplification of avian HEV RNA compared to that achieved by the single assay. The sensitivity of the real-time RT-PCR assay was comparable to that of conventional RT-PCR, and it was shown to be highly specific, as tissues from uninfected chickens, mammalian HEVs, and other viral genomes did not produce positive signals. All tested field samples with virus belonging to different avian HEV genotypes were successfully detected with this new duplex TaqMan real-time RT-PCR assay.