Journal of Virological Methods

BackgroundComparing the in vitro fitness of dengue virus (DENV) isolates is a pivotal approach to assess the contribution of DENV strains replicative fitness to epidemiological contexts, including serotype replacements. Competition assays are the gold standard to compare the in vitro replicative fitness of viral strains. Implementing competition assays between DENV serotypes requires an experimental setup and an appropriate read-out to quantify the viral progeny of strains belonging to different serotypes. ResultsIn the current study, we optimized an existing serotyping qRT-PCR by adapting primer/probe design and multiplexing the serotype-specific qRT-PCR reactions, allowing to accurately detect and quantify all four DENV serotypes. The qRT-PCR was specific, had a limit of detection of at least 5.08x101, 5.16x101, 7.14x101 and 1.36 x101 genome copies/{micro}L, an efficiency of 1.993, 1.975, 1.902, 1.898 and a linearity (R{superscript 2}) of 0.99975, 0.99975, 0.9985, 0.99965 for DENV-1, -2, -3 and -4 respectively. Challenge of this multiplex serotype-specific qRT-PCR on mixes of viral supernatants containing known concentrations of strains from two serotypes evidenced an accurate quantification of the amount of genome copies of each serotype. We next developed an in vitro assay to compare the replicative fitness of two DENV serotypes in the human hepatic cell line HuH7: quantification of the viral progeny of each serotype in the inoculum and the supernatant using the serotype-specific multiplex qRT-PCR unveiled an enrichment of the supernatant in DENV-1 genome copies, uncovering the enhanced replicative fitness of this DENV-1 isolate. ConclusionsThis optimized qRT-PCR combined to a relevant cellular model allowed to accurately quantify the viral progeny of two DENV strains belonging to two different serotypes in a competition assay, allowing to determine which strain had a replicative advantage. This reliable experimental setup is adaptable to the comparative study of the replicative fitness of any DENV serotypes.

The World Health Organization (WHO) has declared the Coronavirus disease 2019 (COVID-19) as an international health emergency. Current diagnostic tests are based on the reverse transcription-quantitative polymerase chain reaction (RT-qPCR) method, the gold standard test that involves the amplification of viral RNA. However, the RT-qPCR assay has limitations in terms of sensitivity and quantification. In this study, we tested both qPCR and droplet digital PCR (ddPCR) to detect low amounts of viral RNA. The cycle threshold (CT) of viral RNA by RT-PCR significantly varied according to the sequence of primer and probe sets with in vitro transcript (IVT) RNA or viral RNA as templates, whereas the copy number of viral RNA by ddPCR was effectively quantified with IVT RNA, cultured viral RNA, and RNA from clinical samples. Furthermore, the clinical samples were assayed via both methods, and the sensitivity of the ddPCR was determined to be significantly higher than RT-qPCR. These findings suggest that ddPCR could be used as a highly sensitive and compatible diagnostic method for viral RNA detection.

COVID-19 (Coronavirus Disease 2019) outbreak was declared a pandemic, by World Health Organization, on March 11, 2020. Viral detection using RT-qPCR has been among the most important factors helping to control local spread of SARS-CoV-2 and it is considered the "gold standard" for diagnosis. Nevertheless, the RNA extraction step is both laborious and expensive, thus hampering the diagnosis in many places where there are not laboratory staff of funds enough to contribute for diagnosis efforts. Thus, the need to simplify procedures, reduce costs of the techniques used, and expand the capacity of the number of diagnostics of COVID-19 is imperative. In this study, detection of SARS-CoV-2 in the absence of RNA extraction has been successfully achieved through pre-treatment of the clinical sample with Proteinase K. The results show that only the use of proteinase K, without the need to perform the whole standard protocol for sample extraction and purification, can be an efficient technique for the diagnosis of COVID-19, since 91% of the samples matched the results with the standard procedure, with an average increase of 5.64 CT in the RT-qPCR.

The current COVID-19 epidemic imposed an unpreceded challenge to the scientific community in terms of treatment, epidemiology, diagnosis, social interaction, fiscal policies and many other areas. The development of accurate and reliable diagnostic tools (high specificity and sensitivity) is crucial in the current period, the near future and in the long term. These assays should provide guidance to identify immune presumptive protected persons, potential plasma, and/or B cell donors and vaccine development among others. Also, such assays will be contributory in supporting prospective and retrospective studies to identify the prevalence and incidence of COVID-19 and to characterize the dynamics of the immune response. As of today, only thirteen serological assays have received the Emergency Use Authorization (EUA) by the U.S. Federal Drug Administration (FDA). In this work we describe the development and validation of a quantitative IgG enzyme-linked immunoassay (ELISA) using the recombinant SARS-CoV-2 Spike Protein S1 domain, containing the receptor-binding domain (RBD), showing 98% sensitivity, 98.9% specificity and positive and negative predictive values of 100% and 99.2%, respectively. The assay showed to be useful to test for SARS-CoV-2 IgG antibodies in plasma samples from COVID-19-recovered subjects as potential donors for plasmapheresis. This assay is currently under review by the Federal Drug Administration for an Emergency Use Authorization request (Submission Number EUA201115).

Effective interventions are mandatory to control the transmission and spread of SARS-CoV-2, a highly contagious virus causing devastating effects worldwide. Cost-effective approaches are pivotal tools required to increase the detection rates and escalate further in massive surveillance programs, especially in countries with limited resources that most of the efforts have focused on symptomatic cases only. Here, we compared the performance of the RT-qPCR using an intercalating dye with the probe-based assay. Then, we tested and compared these two RT-qPCR chemistries in different pooling systems: after RNA extraction (post-RNA extraction) and before RNA extraction (pre-RNA extraction) optimizing by pool size and template volume. We evaluated these approaches in 610 clinical samples. Our results show that the dye-based technique has a high analytical sensitivity similar to the probe-based detection assay used worldwide. Further, this assay may also be applicable in testing by pool systems post-RNA extraction up to 20 samples. However, the most efficient system for massive surveillance, the pre-RNA extraction pooling approach, was obtained with the probe-based assay in test up to 10 samples adding 13.5 {micro}L of RNA template. The low cost and the potential use in pre-RNA extraction pool systems, place of this assays as a valuable resource for scalable sampling to larger populations. Implementing a pool system for population sampling results in an important savings of laboratory resources and time, which are two key factors during an epidemic outbreak. Using the pooling approaches evaluated here, we are confident that it can be used as a valid alternative assay for the detection of SARS-CoV-2 in human samples.

Flow cytometry is an established method for the detection and enumeration of viruses. However, the technique is unable to target specific viral species. Here, we present OligoFlow, a novel method for the rapid detection and enumeration of viruses by incorporating flow cytometry with species specific oligonucleotide hybridization. Using Ostried herpesvirus and dengue virus as model organisms, we demonstrate high-level detection and specificity. Our results represent a significant advancement in viral flow cytometry, opening the possibilities for the rapid identification of viruses in time critical settings.

A novel coronavirus (severe acute respiratory syndrome coronavirus 2, SARS-CoV-2) emerged in late 2019, causing an outbreak of pneumonia [coronavirus disease 2019 (COVID-19)] in Wuhan, China, which then rapidly spread globally. Although the use of ready-made reaction mixes can enable more rapid PCR-based diagnosis of COVID-19, the need to transport and store these mixes at low temperatures presents challenges to already overburdened logistics networks. Here, we present an optimized freeze-drying procedure that allows SARS-CoV-2 PCR mixes to be transported and stored at ambient temperatures, without loss of activity. Additive-supplemented PCR mixes were freeze-dried. The residual moisture of the freeze-dried PCR mixes was measured by Karl-Fischer titration. We found that freeze-dried PCR mixes with [~]1.2% residual moisture are optimal for storage, transport, and reconstitution. The sensitivity, specificity, and repeatability of the freeze-dried reagents were similar to those of freshly prepared, wet reagents. The freeze-dried mixes retained activity at room temperature (18[~]25{degrees}C) for 28 days, and for 14 and 10 days when stored at 37{degrees}C and 56{degrees}C, respectively. The uptake of this approach will ease logistical challenges faced by transport networks and make more cold storage space available at diagnosis and hospital laboratories. This method can also be applied to the generation of freeze-dried PCR mixes for the detection of other pathogens.

Due to urgency and demand, numerous severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) immunoassays are rapidly being developed and placed on the market with limited validation on clinical samples. Thorough validation of serological tests are required to facilitate their use in the accurate diagnosis of SARS-CoV-2 infection, confirmation of molecular results, contact tracing, and epidemiological studies. This study evaluated the sensitivity and specificity of nine commercially available serological tests. These included three enzyme-linked immunosorbent assays (ELISAs) and six point-of-care (POC) lateral flow tests. The assays were validated using serum samples from: i) SARS-CoV-2 PCR-positive patients with a documented first day of disease; ii) archived sera obtained from healthy individuals before the emergence of SARS-CoV-2 in China; iii) sera from patients with acute viral respiratory tract infections caused by other coronaviruses or non-coronaviruses; and iv) sera from patients positive for dengue virus, cytomegalovirus and Epstein Barr virus. The results showed 100% specificity for the Wantai SARS-CoV-2 Total Antibody ELISA, 93% for the Euroimmun IgA ELISA, and 96% for the Euroimmun IgG ELISA with sensitivities of 90%, 90%, and 65%, respectively. The overall performance of the POC tests according to manufacturer were in the rank order of AutoBio Diagnostics > Dynamiker Biotechnology = CTK Biotech > Artron Laboratories > Acro Biotech [≥] Hangzhou Alltest Biotech. Overall, these findings will facilitate selection of serological assays for the detection SARS-CoV-2-specific antibodies towards diagnosis as well as sero-epidemiological and vaccine development studies.

BackgroundThe current increase in the spread of (SARS-CoV-2) critically needs a multitarget diagnostic assays to promote analytical sensitivity to facilitate the public health actions. ObjectiveThe aim of this study was to develop a new primer-probe set targeting N gene of SARS-CoV-2 to improve the sensitivity for detection of COVID-19(Corona Virus Disease 2019)in multiplex rRT-PCR (Reversetranscript Realtime PCR) and ddPCR (Droplet Digital PCR). ResultsWe designed primers/probes set N(LZU3) targeting the N gene of 2019-nCov and proved its sensitivity in both rRT-PCR and ddPCR. When the quantity of template was 105 copies/reaction, the mean Ct value of N(LZU3) was 32.563, the detection rate was 91.7%. If the quantity of template was 52.5 copies/reaction, the mean Ct value of N(LZU3) was 33.835, and the detection rate was 83.3%, which were similar with that of N(CDC) and N(USA). The calculated lower limit of detection (LOD) of the new primer-probe set N(LZU3) used in rRT-PCR was 118 copies/reaction. We also did one-step ddPCR for detection the same serial dilution of RNA template. It shows good linearity for primer/probe sets N(LZU3). The calculated lower limit of detection (LOD) of N(LZU3) was 22.4 copies/reaction, which was 1.12 copies/ul. ConclusionThe novel primer-probe set(LZU3) targeting N gene of SARS-CoV-2 could be both used in rRT-PCR and ddPCR with better sensitivity, furthermore, ddPCR method had higer sensitivity than rRT-PCR, hence it could significantly improve SARS-CoV-2 detection efficiency in low virus load and asymptomatic infection.

A one-step reverse transcription and real-time PCR (RT-qPCR) test was developed for rapid screening (40 minutes) of the Spike N501Y and HV69-70del mutations in SARS-CoV-2 positive samples. The test also targets a conserved region of SARS-CoV-2 Orf1ab as an internal control. The samples containing both the N501Y and HV69-70del mutations are concluded as VOC-202012/01 positive. Samples suspected to be positive for B.1.351 or P.1 are the N501Y positive and HV69-70del negative cases. Limit of detection (LOD) of the kit for Orf1ab target is 500 copies/mL, while that of the N501, Y501 and HV69-70del targets are 5000 copies/mL. The developed assay was applied to 165 clinical samples containing SARS-CoV-2 from 32 different lineages. The SARS-CoV-2 lineages were determined via the next-generation sequencing (NGS). The RT-qPCR results were in 100% agreement with the NGS results that 19 samples were N501Y and HV69-70del positive, 10 samples were N501Y positive and HV69-70del negative, 1 sample was N501Y negative and HV69-70del positive, and 135 samples were N501Y and HV69-70del negative. All the VOC-202012/01 positive samples were detected in people who have traveled from England to Turkey. The RT-qPCR test and the Sanger sequencing was further applied to 1000 SARS-CoV-2 positive clinical samples collected in Jan2021 from the 81 different provinces of Turkey. The RT-qPCR results were in 100% agreement with the Sanger sequencing results that 32 samples were N501Y positive and HV69-70del negative, 4 samples were N501Y negative and HV69-70del positive, 964 samples were N501Y and HV69-70del negative. The specificity of the 40 minutes RT-qPCR assay relative to the sequencing-based technologies is 100%. The developed assay is an advantageous tool for timely and representative estimation of the N501Y positive variants prevalence because it allows testing a much higher portion of the SARS-CoV-2 positives in much lower time compared to the sequencing-based technologies.

Lassa fever is a severe, often fatal febrile illness endemic to West Africa caused by Lassa virus (LASV). The viral nucleoprotein (NP) is a target antigen for serological assays to identify previous exposure to LASV. To our knowledge, there is no commercially available assay that reliably quantifies anti-LASV-NP IgG antibodies in human serum. We report the development and qualification of an ELISA designed to detect and quantify anti-LASV-NP IgG in human serum samples. The assay employs recombinant Lineage IV LASV-NP immobilized on microwells to capture NP-specific IgG antibodies, which are then detected using horseradish peroxidase-conjugated anti-human IgG followed by TMB substrate and reading of optical densities. Optimal assay reagent concentrations, incubation times and temperature were determined along with assay positivity criteria and dynamic range. A reference standard prepared from pooled sera from donors in endemic Lassa fever regions was established and calibrated to the first WHO international standard for LASV antibodies. High and low positive controls for assay quality control were generated. Naive human serum was used as a negative control. Following assay optimization, performance was assessed through assay qualification. The assay positivity criteria, lower limit of detection, upper and lower limits of quantitation, inter-assay precision, selectivity and dilutional linearity were determined. Our anti-LASV-NP IgG ELISA was shown to reliably measure anti-LASV-NP IgG levels in human serum. The method demonstrated sensitivity, intra- and inter-assay precision, dilution linearity across its analytical range and specificity for anti-LASV-NP IgG. Establishing this assay represents an essential step toward strengthening LASV epidemiology research and supporting urgently needed development of a vaccine to prevent Lassa Fever.

The world is currently facing an unprecedented pandemic caused by the novel coronavirus SARS-CoV-2 (COVID-19) which was first reported in late 2019 by China to the World Health Organization (WHO). The containment strategy for COVID-19, which has non-specific flu-like symptoms and where upwards of 80% of the affected has either mild or no symptoms, is critically centered upon diagnostic testing, tracking and isolation. Thus, the development of specific and sensitive diagnostic tests for COVID-19 is key towards the first successful step of disease management. Public health organizations like the WHO and the US-based Centers for Disease Control and Prevention (CDC) have developed real-time PCR (RT-PCR) based diagnostic tests to aid in the detection of acute infection. In this study we sought to modify the CDC RT-PCR diagnostic assay protocol to increase its sensitivity and to make the assay directly portable to health care providers in a community-based hospital setting. A number of modifications to the original protocol were tested. Increasing the RT-PCR annealing temperature by 7{degrees}C to 62{degrees}C was associated with the most significant improvement in sensitivity, wherein the cycle-threshold (Ct) value for the N2 assay was reduced by [~]3 units, in effect both reducing the overall number of inconclusive results and yielding N1/N2 assays to have similar Ct values. The limit of detection of the modified assay was also improved (0.86 RNA copies/{micro}l for both nCoV 2019_N1/N2 assays) compared to the CDC RT-PCR diagnostic assay (1 and 3.16 RNA copies/{micro}l for nCoV 2019_N1 and N2 assay, respectively). Using this modification, there was no significant effect on SARS-CoV-2 detection rate when viral RNA extraction was performed either manually or through an automated extraction method. We believe this modified protocol allows for more sensitive detection of the virus which in turn will be useful for pandemic management.

Accurate identification of individuals infected with SARS-CoV-2 is crucial for efforts to control the ongoing COVID-19 pandemic. Polymerase chain reaction (PCR)-based assays are the gold standard for detecting viral RNA in patient samples and are used extensively in clinical settings. Most currently used quantitative PCR (RT-qPCRs) rely upon real-time detection of PCR product using specialized laboratory equipment. To enable the application of PCR in resource-poor or non-specialist laboratories, we have developed and evaluated a nested PCR method for SARS-CoV-2 RNA using simple agarose gel electrophoresis for product detection. Using clinical samples tested by conventional qPCR methods and RNA transcripts of defined RNA copy number, the nested PCR based on the RdRP gene demonstrated high sensitivity and specificity for SARS-CoV-2 RNA detection in clinical samples, but showed variable and transcript length-dependent sensitivity for RNA transcripts. Samples and transcripts were further evaluated in an additional N protein real-time quantitative PCR assay. As determined by 50% endpoint detection, the sensitivities of three RT-qPCRs and nested PCR methods varied substantially depending on the transcript target with no method approaching single copy detection. Overall, these findings highlight the need for assay validation and optimization and demonstrate the inability to precisely compare viral quantification from different PCR methodologies without calibration.

The COVID-19 pandemic caused by the SARS-CoV-2 virus has placed extensive strain on RNA isolation and RT-qPCR reagents. Rapid development of new test kits has helped to alleviate these shortages. However, comparisons of these new detection systems are largely lacking. Here, we compare indirect methods that require RNA extraction, and direct RT-qPCR on patient samples. For RNA isolation we compared four different companies (Qiagen, Invitrogen, BGI and Norgen Biotek). For detection we compared two recently developed Taqman-based modules (BGI and Norgen Biotek), a SYBR green-based approach (NEB Luna Universal One-Step Kit) with published and newly-developed primers, and clinical results (Seegene STARMag RNA extraction system and Allplex 2019-nCoV RT-qPCR assay). Most RNA isolation procedures performed similarly, and while all RT-qPCR modules effectively detected purified viral RNA, the BGI system proved most sensitive, generating comparable results to clinical diagnostic data, and identifying samples ranging from 65 copies - 2.1x105 copies of viral Orf1ab/l. However, the BGI detection system is [~]4x more expensive than other options tested here. With direct RT-qPCR we found that simply adding RNase inhibitor greatly improved sensitivity, without need for any other treatments (e.g. lysis buffers or boiling). The best direct methods were [~]10 fold less sensitive than indirect methods, but reduce sample handling, as well as assay time and cost. These studies will help guide the selection of COVID-19 detection systems and provide a framework for the comparison of additional systems.

Human Cytomegalovirus (HCMV) infection represents a life-threating pathogen for immunocompromised patients. Molecular quantitative testing on whole blood or plasma represents the gold standard for diagnosis of invasive HCMV infection and for monitoring antiviral treatment in individuals at risk of CMV disease. For these reasons, accurate standardization towards the 1st WHO International standard between different centres and diagnostic kits represent an effort for a better clinical management of CMV-positive patients. Herein, we evaluate for the first time the performance of a new TMA (Transcription Mediated Amplification) kit towards qPCR chemistry, used as routine method, on whole blood samples. 755 clinical whole blood specimens were collected and simultaneously tested with TMA and qPCR assays. Data showed 99.27% agreement for positive quantified samples and 89.39% agreement for those not detected between two tested methods. Evaluation of viraemia in positive samples highlighted a good correlation for TMA and qPCR chemistries in terms of International Units ({Delta}Log10 IU/ml: - 0.29 {+/-} 0.40). TMA assay showed a significant correlation with qPCR also in monitored patients until three months, thus allowing accurate evaluation of viraemia in transplanted patients. Moreover, preliminary data about analytical sensitivity of TMA chemistry onto DBS samples showed 86.54% correlation with whole blood specimens. Thus, TMA chemistry showed a good agreement with qPCR assay, used as current diagnostic routine, and offers important advantages: FDA and IVD approval on plasma and whole blood, automated workflow with minimal hands-on time, random access loading, thus enabling a rapid and reliable diagnostics in HCMV-infected patients.

Dengue virus (DENV) is the cause of dengue / severe dengue and a virus of the Flaviviridae family, furthermore, dengue fever has rapidly spread in the world in recent decades. DENV is transmitted by female mosquitoes, mainly of the specie Aedes aegypti. The main method to control or prevent the transmission of DENV is to combat the mosquito vectors. Among these, one of important methods is to monitor the DENVs in the mosquito vectors. For the detection of DENV, nucleic acid amplification tests (NAAT) were recommended, of which criterion standard is real-time RT-PCR with highly sensitive and specific. However, it takes long time as to judge the result per a reaction, besides the necessity of the treatment of RNA in advance, example of extraction, concentration and purification. It was our object in this time to develop the method of real-time RT-PCR detecting DENVs in shorter time, moreover without especial treatment of RNA from the mosquito in advance. Besides, this work was performed with combing the mobile real-time PCR device with the one-step RT-PCR reagent. Firstly, we succeeded in shortening the time of real-time RT-PCR for the detection of DENV per one reaction, so that the judgement needed less than 20 minutes if genomic RNA treated in advance. Moreover, each value on the real-PCR device was quantitatively correlated with the positive control RNA from 1.0 x 10 ^ 3 copies to 1.0 x 10 ^ 0 copies per reaction (This correlation coefficient R2 > 0.95). Additionally, it made sure that this method could be applied to each DENV serotype. Secondly, we established the basis of procedure for the real-time RT-PCR without the treatment in advance so-called "direct". As the result that the positive control RNA additive was utilized instead of the real DENV, spiked into the mosquito homogenized and sampled the supernatant without treatment, it was possible to detect on the real-time RT-PCR even if mosquitoes immediately after blood-feeding. For this reason, this method might be able to utilize in human sera, too. According to the results of this work, we could suggest the method is possible to detect DENV more quickly and more simply than heretofore. The Real-time "direct" RT-PCR, especially, could be performed with mobile real-time PCR PCR1100 device and one step RT-PCR reagent only. This method must help to detect some viruses other than DENV, too.

AimTo develop a rapid and easy diagnostic assay for detection of SARS-CoV-2 RNA presented in saliva samples. MethodThe color-based RT-LAMP was used to detect nucleocapsid (N) gene of SARS-CoV-2 without RNA extraction from saliva. ResultsRNA spiked saliva can be used directly for cDNA synthesis after heat inactivation of the saliva and diluted 2-fold with either water or PBS. For both PCR and LAMP, 20% of saliva did not have obvious effect on the reaction. Saliva did not interfere with RT-LAMP when the volume of saliva was less than 20% of the total volume. The sensitivity of the RT-LAMP reached to 1.034x10-5 ng/{micro}l (475 copies/l). The RT-LAMP assay was validated by testing 20 RNA spiked saliva samples. The assay specificity was similar to that of data without saliva. ConclusionsThe RT-LAMP colorimetric assay can be used as a screening method with the advantages of being rapid, easy to use than the qRT-PCR.

BackgroundThe colloidal gold immunochromatography assay (GICA) is a rapid diagnostic tool for novel coronavirus disease 2019 (COVID-19) infections. However, with significant numbers of false negatives, improvements to GICA are needed. MethodsSix recombinant HCoV-19 nucleocapsid and spike proteins were prepared and evaluated. The optimal proteins were employed to develop a sandwich-format GICA strip to detect total antibodies (IgM and IgG) against HCoV-19. GICAs performance was assessed with comparison of viral RNA detection. ResultsRecombinant HCoV-19 proteins were obtained, including three prokaryotically expressed rN, rN1, rN2 nucleocapsid proteins, and three eukaryotically expressed rS1, rS-RBD, rS-RBD-mFc spike proteins. The recombinant proteins with the highest ELISA titers (rS1 and rS-RBD-mFc) against coronavirus-specific IgM and IgG were chosen for GICA development. The GICA has a sensitivity and specificity of 86.89% (106/122) and 99.39% (656/660), respectively. Furthermore, 65.63% (21/32) of the clinically confirmed but RT-PCR negative samples were GICA positive. ConclusionsThe eukaryotically-expressed spike proteins (rS1and rS-RBD-mFc) are more suitable than the prokaryotically expressed nucleocapsid proteins for HCoV-19 serological diagnosis. The GICA sandwich used to detect total antibodies is a powerful complement to the current standard RNA-based tests.

Quick and accurate detection of neutralizing antibodies (nAbs) against yellow fever is essential in serodiagnosis during outbreaks, for surveillance and to evaluate vaccine efficacy in population-wide studies. All this requires serological assays that can process a large number of samples in a highly standardized format. Albeit being laborious, time-consuming and limited in throughput, classical plaque reduction neutralization test (PRNT) is still considered gold standard for the detection and quantification of nAbs due to its sensitivity and specificity. Here we report the development of an alternative fluorescence-based serological assay (SNTFLUO) with an equally high sensitivity and specificity that is fit for high-throughput testing with the potential for automation. Finally, our novel SNTFLUO was cross-validated in several reference laboratories and against international WHO standards showing its potential to be implemented in clinical use. SNTFLUO assays with similar performance are available for the Japanese encephalitis, Zika and dengue viruses amenable for differential diagnostics. IMPORTANCEFast and accurate detection of neutralizing antibodies (nAbs) against yellow fever virus (YFV) is key in yellow fever serodiagnosis, outbreak surveillance and monitoring of vaccine efficacy. Although classical PRNT still remains gold standard for measuring YFV nAbs, this methodology suffers from inherent limitations such as a low throughput and an overall high labor intensity. We present a novel fluorescence-based serum neutralization test (SNTFLUO) with equally high sensitivity and specificity that is fit for processing large number of samples in a highly standardized manner and has the potential to be implemented in clinical use. In addition, we present SNTFLUO assays with similar performance for Japanese encephalitis, Zika and dengue viruses opening new avenues for differential diagnostics.

The COVID-19 pandemic resulted in lockdowns all over the world thus affecting nearly all aspects of social life and also had a huge impact on global economies. Since vaccines and therapies are still not available for the population, prevention becomes desperately needed. One important aspect for prevention is the identification and subsequent isolation of contagious specimens. The currently used methods for diagnostics are time consuming and also hindered by the limited availability of reagents and reaction costs, thus presenting a bottle neck for prevention of COVID-19 spread. Here, we present a new ultra-fast test method which is ten times faster than conventional diagnostic tests using real time quantitative PCR (RT-qPCR). In addition, this ultra-fast method is easy to handle as well as cost effective. We translated published SARS-CoV-2 testing protocols from the Centers of Disease Control and Prevention (Atlanta, Georgia, USA) and the Charite Berlin (Germany) to the NEXTGENPCR (NGPCR) machine and combined it with a fluorescence-based endpoint measurement. Fluorescence was measured with a commercial blue light scanner. We confirmed the NEXTGENPCR results with commercially available positive controls. In addition, we isolated RNA from SARS-CoV-2 infected patients and achieved similar results to clinical RT-qPCR assays. Here, we could show correlation between the results obtained by NEXTGENPCR and conventional RT-qPCR.