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In December 2019, the novel betacoronavirus Severe Acute Respiratory Disease Coronavirus 2 (SARS-CoV-2) was first detected in Wuhan, China. SARS-CoV-2 has since become a pandemic virus resulting in hundreds of thousands of deaths and deep socioeconomic implications worldwide. In recent months, efforts have been directed towards detecting, tracking, and better understanding human humoral responses to SARS-CoV-2 infection. It has become critical to develop robust and reliable serological assays to characterize the abundance, neutralization efficiency, and duration of antibodies in virus-exposed individuals. Here we review the latest knowledge on humoral immune responses to SARS-CoV-2 infection, along with the benefits and limitations of currently available commercial and laboratory-based serological assays. We also highlight important serological considerations, such as antibody expression levels, stability and neutralization dynamics, as well as cross-reactivity and possible immunological back-boosting by seasonal coronaviruses. The ability to accurately detect, measure and characterize the various antibodies specific to SARS-CoV-2 is necessary for vaccine development, manage risk and exposure for healthcare and at-risk workers, and for monitoring reinfections with genetic variants and new strains of the virus. Having a thorough understanding of the benefits and cautions of standardized serological testing at a community level remains critically important in the design and implementation of future vaccination campaigns, epidemiological models of immunity, and public health measures that rely heavily on up-to-date knowledge of transmission dynamics.

Abstract Background The association between SARS-CoV-2 commercial serological assays and virus neutralization test (VNT) has been poorly explored in mild patients with COVID-19. Methods 439 serum specimens were longitudinally collected from 76 healthcare workers with RT-PCR-confirmed COVID-19. The clinical sensitivity (determined weekly) of 9 commercial serological assays were evaluated. Clinical specificity was assessed using 69 pre-pandemic sera. Correlation, agreement, and concordance with the VNT were also assessed on a subset of 170 samples. Area under the ROC curve (AUC) was estimated at 2 neutralizing antibody titers. Results The Wantai Total Ab assay targeting the receptor binding domain (RBD) within the S protein presented the best sensitivity at different times during the course of disease. The clinical specificity was greater than 95% for all tests except for the Euroimmun IgA assay. The overall agreement with the presence of neutralizing antibodies ranged from 62.2% (95%CI; 56.0–68.1) for bioMérieux IgM to 91.2% (87.0–94.2) for Siemens. The lowest negative percent agreement (NPA) was found with the Wantai Total Ab assay (NPA 33% (21.1–48.3)). The NPA for other total Ab or IgG assays targeting the S or the RBD was 80.7% (66.7–89.7), 90.3% (78.1–96.1), and 96.8% (86.8–99.3) for Siemens, bioMérieux IgG, and DiaSorin, respectively. None of the commercial assays have sufficient performance to detect a neutralizing titer of 80 (AUC < 0.76). Conclusions Although some assays show a better agreement with VNT than others, the present findings emphasize that commercialized serological tests, including those targeting the RBD, cannot substitute a VNT for the assessment of functional antibody response.

One of the key challenges of the recent COVID-19 pandemic is the ability to accurately estimate the number of infected individuals, particularly asymptomatic and/or early-stage patients. We herewith report the proof-of-concept development of a biosensor able to detect the SARS-CoV-2 S1 spike protein expressed on the surface of the virus. The biosensor is based on membrane-engineered mammalian cells bearing the human chimeric spike S1 antibody. We demonstrate that the attachment of the protein to the membrane-bound antibodies resulted in a selective and considerable change in the cellular bioelectric properties measured by means of a Bioelectric Recognition Assay. The novel biosensor provided results in an ultra-rapid manner (3 min), with a detection limit of 1 fg/mL and a semi-linear range of response between 10 fg and 1 μg/mL. In addition, no cross-reactivity was observed against the SARS-CoV-2 nucleocapsid protein. Furthermore, the biosensor was configured as a ready-to-use platform, including a portable read-out device operated via smartphone/tablet. In this way, we demonstrate that the novel biosensor can be potentially applied for the mass screening of SARS-CoV-2 surface antigens without prior sample processing, therefore offering a possible solution for the timely monitoring and eventual control of the global coronavirus pandemic.

We aimed to review the existing literature on the different types of neutralization assays and international standards for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). We comprehensively summarized the serological assays for detecting neutralizing antibodies against SARS-CoV-2 and demonstrated the importance of an international standard for calibrating the measurement of neutralizing antibodies. Following the coronavirus disease outbreak in December 2019, there was an urgent demand to detect neutralizing antibodies in patients or vaccinated people to monitor disease outcomes and determine vaccine efficacy. Therefore, many approaches were developed to detect neutralizing antibodies against SARS-CoV-2, such as microneutralization assay, SARS-CoV-2 pseudotype virus assay, enzyme-linked immunosorbent assay (ELISA), and rapid lateral flow assay. Given the many types of serological assays for quantifying the neutralizing antibody titer, the comparison of different assay results is a challenge. In 2020, the World Health Organization proposed the first international standard as a common unit to define neutralizing antibody titer and antibody responses against SARS-CoV-2. These standards are useful for comparing the results of different assays and laboratories.

More than three years ago, the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) caused the unforeseen COVID-19 pandemic with millions of deaths. In the meantime, SARS-CoV-2 has become endemic and is now part of the repertoire of viruses causing seasonal severe respiratory infections. Due to several factors, among them the development of SARS-CoV-2 immunity through natural infection, vaccination and the current dominance of seemingly less pathogenic strains belonging to the omicron lineage, the COVID-19 situation has stabilized. However, several challenges remain and the possible new occurrence of highly pathogenic variants remains a threat. Here we review the development, features and importance of assays measuring SARS-CoV-2 neutralizing antibodies (NAbs). In particular we focus on in vitro infection assays and molecular interaction assays studying the binding of the receptor binding domain (RBD) with its cognate cellular receptor ACE2. These assays, but not the measurement of SARS-CoV-2-specific antibodies per se, can inform us of whether antibodies produced by convalescent or vaccinated subjects may protect against the infection and thus have the potential to predict the risk of becoming newly infected. This information is extremely important given the fact that a considerable number of subjects, in particular vulnerable persons, respond poorly to the vaccination with the production of neutralizing antibodies. Furthermore, these assays allow to determine and evaluate the virus-neutralizing capacity of antibodies induced by vaccines and administration of plasma-, immunoglobulin preparations, monoclonal antibodies, ACE2 variants or synthetic compounds to be used for therapy of COVID-19 and assist in the preclinical evaluation of vaccines. Both types of assays can be relatively quickly adapted to newly emerging virus variants to inform us about the magnitude of cross-neutralization, which may even allow us to estimate the risk of becoming infected by newly appearing virus variants. Given the paramount importance of the infection and interaction assays we discuss their specific features, possible advantages and disadvantages, technical aspects and not yet fully resolved issues, such as cut-off levels predicting the degree of in vivo protection.

Newcastle disease (ND) is an acute and highly contagious disease caused by the Newcastle disease virus (NDV) infecting poultry, which has caused great harm to the poultry industry around the world. Rapid diagnosis of NDV is important to early treatment and early institution of control measures. In this review, we comprehensively summarize the most recent research into NDV, including historical overview, molecular structure, and infection mechanism. We then focus on detection strategies for NDV, including virus isolation, serological assays (such as hemagglutination and hemagglutination-inhibition tests, enzyme linked immunosorbent assay, reporter virus neutralization test, Immunofluorescence assay, and Immune colloidal gold technique), molecular assays (such as reverse transcription polymerase chain reaction, real-time quantitative PCR, and loop-mediated isothermal amplification) and other assays. The performance of the different serological and molecular biology assays currently available was also analyzed. To conclude, we examine the limitations of currently available strategies for the detection of NDV to lay the groundwork for new detection assays.

The existence of a substantial but unclear number of asymptomatic SARS-COV-2 patients worldwide has raised concerns among global public health authorities. In this review, according to the published literature, we provided the evidence that asymptomatic infections can result in person-to-person transmission. Four studies suggested that the virus can be transmitted by asymptomatic patients for at least two consecutive generations, indicating its strong infectivity. Asymptomatic infection tends to be, but is not only, identified among young people (<20 years old). The majority of asymptomatic patients appear to have a milder clinical course during hospitalization, but the severity of the symptoms of the secondary patients infected by SARS-COV-2 from asymptomatic patients varies with their physical constitution. The proportion of asymptomatic individuals among all confirmed cases widely differed (from 1.95% to 87.9%) according to the study setting and the populations studied. The increasing large-scale tests are expected to give more information about the true number of asymptomatic infections in the population. In China and other countries, various guidelines for management of asymptomatic cases have been issued. Importantly, early detection, early reporting, early isolation and early treatment of asymptomatic patients require the joint efforts of policy makers, clinicians, technicians, epidemiologists, virologists and patients.

The recent outbreak of a novel Coronavirus (SARS-CoV-2) and its rapid spread across the continents has generated an urgent need for assays to detect the neutralising activity of human sera or human monoclonal antibodies against SARS-CoV-2 spike protein and to evaluate the serological immunity in humans. Since the accessibility of live virus microneutralisation (MN) assays with SARS-CoV-2 is limited and requires enhanced bio-containment, the approach based on “pseudotyping” can be considered a useful complement to other serological assays. After fully characterising lentiviral pseudotypes bearing the SARS-CoV-2 spike protein, we employed them in pseudotype-based neutralisation assays in order to profile the neutralising activity of human serum samples from an Italian sero-epidemiological study. The results obtained with pseudotype-based neutralisation assays mirrored those obtained when the same panel of sera was tested against the wild type virus, showing an evident convergence of the pseudotype-based neutralisation and MN results. The overall results lead to the conclusion that the pseudotype-based neutralisation assay is a valid alternative to using the wild-type strain, and although this system needs to be optimised and standardised, it can not only complement the classical serological methods, but also allows serological assessments to be made when other methods cannot be employed, especially in a human pandemic context.

Toxoplasma gondii is an intracellular parasite capable of crossing the placenta in pregnancy and infecting the developing fetus, leading to various congenital anomalies and even abortion. Acute Toxoplasma infection is responsible for almost all cases of congenital toxoplasmosis in immunocompetent pregnant women. Prenatal screening for acute toxoplasmosis primarily involves maternal serology and fetal ultrasound imaging. When serological or ultrasound findings suggest acute infection, further diagnostic tests are necessary to confirm fetal infection. Currently, molecular methods to detect the parasite’s DNA, including polymerase chain reaction-based methods, on amniotic fluid are the gold standard tests for the diagnosis of congenital toxoplasmosis. In this review, we aim to discuss various aspects of screening and diagnostic methods for toxoplasmosis in pregnancy, including (i) current serological assays, screening approaches, and future perspectives; (ii) the role of imaging techniques, with an emphasis on ultrasound; (iii) principles and recent advances in diagnostic molecular methods; (iv) emerging techniques, such as point-of-care-based tests and biosensors, and microRNAs as novel biomarkers of acute infection; and (v) an overview of screening programs in different countries, important epidemiological determinants, and recommendations for Toxoplasma screening health policies.

The in-house ELISA SARS-CoV-2 serological assay, developed by the Armauer Hansen Research Institute (AHRI) in Ethiopia, measures anti-SARS-CoV-2 receptor binding domain (RBD) antibodies. This study aimed to compare the performance of our cost-effective in-house ELISA with two established commercially available SARS-CoV-2 antibody detection assays during the pre-Omicron COVID-19 pandemic. In April 2021, serum samples were collected from 1441 students across 60 schools in Oromia, from 15 hotspot districts and towns. Socio-demographic data were gathered using CSentryCSProDataEntry7.2.1. Performance agreements between AHRI’s in-house ELISA and the two commercial assays were analyzed in these serum samples. Statistical analyses, including Cohen’s kappa (κ), overall percentage agreement, positive percent agreement (PPA), and negative percent agreement (NPA), were performed using STATA software. Diagnostic parameters were presented with 95% confidence intervals (CI), calculated using the Clopper-Pearson method. The performance comparison of the in-house ELISA showed substantial agreement with the two commercial assays. The overall concordance rate between in-house ELISA and Elecsys CLIA was 80.8% (95% CI 75.0–86.5), while the agreement between in-house ELISA and the Rapid LFA test (IgG + IgM) was 75.8% (95% CI 70.1–81.5). The kappa coefficients were: in-house ELISA vs. Elecsys CLIA (κ = 0.61, 95% CI 0.55–0.67), in-house ELISA vs. Rapid LFA test (IgG + IgM) (κ = 0.52, 95% CI 0.46–0.58), and Elecsys CLIA vs. Rapid LFA test (IgG + IgM) (κ = 0.73, 95% CI 0.67–0.78). The in-house ELISA demonstrated strong agreement with the Elecsys CLIA, showing a PPA of 81.7% and an NPA of 80.1%. Compared to the Rapid LFA test (IgG + IgM), which had a PPA of 83% and an NPA of 70.4%, the in-house ELISA exhibited better overall agreement with Elecsys CLIA. This study’s findings indicate substantial agreement between the in-house ELISA and Elecsys. However, only modest agreement was observed between the in-house ELISA and the rapid test (IgG + IgM). Together, these results suggest the utility of the in-house ELISA as a cost-effective tool for sero surveillance studies and monitoring the effect of interventions in resource-poor settings.