Multiplex microsphere immunoassays for the detection of IgM and IgG to arboviral diseases

Laboratory Testing for Powassan Virus: Past, Present, and Future

Powassan virus is a tick-borne flavivirus that can cause severe neuroinvasive disease, with areas of endemicity in the Northeast and Midwest United States, Canada, and Russia. Diagnosis is challenging and relies on a high index of suspicion and choosing the right test based on duration of infection and the patient's immune status. This review covers laboratory testing for Powassan virus, including historical considerations, modern options, and methods being developed in the research space.

Dengue: A review of laboratory diagnostics in the vaccine age

Background. Dengue is an important arboviral infection of considerable public health significance. It occurs in a wide global belt within a variety of tropical regions. The timely laboratory diagnosis of Dengue infection is critical to inform both clinical management and an appropriate public health response. Vaccination against Dengue virus is being introduced in some areas.Discussion. Appropriate diagnostic strategies will vary between laboratories depending on the available resources and skills. Diagnostic methods available include viral culture, the serological detection of Dengue-specific antibodies in using enzyme immunoassays (EIAs), microsphere immunoassays, haemagglutination inhibition or in lateral flow point of care tests. The results of antibody tests may be influenced by prior vaccination and exposure to other flaviviruses. The detection of non-structural protein 1 in serum (NS1) has improved the early diagnosis of Dengue and is available in point-of-care assays in addition to EIAs. Direct detection of viral RNA from blood by PCR is more sensitive than NS1 antigen detection but requires molecular skills and resources. An increasing variety of isothermal nucleic acid detection methods are in development. Timing of specimen collection and choice of test is critical to optimize diagnostic accuracy. Metagenomics and the direct detection by sequencing of viral RNA from blood offers the ability to rapidly type isolates for epidemiologic purposes.Conclusion. The impact of vaccination on immune response must be recognized as it will impact test interpretation and diagnostic algorithms.

Association between seroprevalence of measles virus in monkeys and degree of human-monkey contact in Bangladesh

Measles infections can cause significant morbidity and mortality in human and monkey populations. The endemicity of measles in human populations and viral circulation within populations of free-living monkeys may have important repercussions for potential zoonotic transmission events and for the long-term health of monkey populations. Yet, there has not yet been a rigorous investigation of the dynamics of measles transmission where human and monkey populations coexist. In this study, to determine the difference in seroprevalence of the measles virus across different contexts of human-monkey contact, we analyzed serum samples collected from 56 apparently healthy Macaca mulatta monkeys who occupied diverse contexts, with different degrees of human-monkey contact, in Bangladesh. This is the first report of measles virus seroprevalence in monkeys in Bangladesh. We found a clear association between measles virus seropositivity in monkeys and the context in which they interact with humans. Seroprevalence was the lowest in wild areas (0.0%) and increased in shrines (4.8%), urban areas (5.9%), and was highest among monkeys who are used as performance animals (50.0%). This work suggests that a One Health approach informed by local interspecies transmission dynamics is necessary to develop strategies that both improve measles vaccination coverage, achieve long-term surveillance in monkey populations, and prevent measles spillback to monkeys. This approach aims to inform conservation efforts and protect the long-term health of human and monkey populations.

Characterization of a monoclonal antibody specific to California serogroup orthobunyaviruses and development as a chimeric immunoglobulin M-positive control in human diagnostics

IMPORTANCE

Orthobunyaviruses in the California serogroup cause severe neurological disease in children and adults. While these viruses are known to circulate widely in North America, their occurrence is rare. Serological testing for CSGVs is hindered by the limited availability and volumes of human-positive specimens needed as controls in serologic assays. Here, we described the development of a murine monoclonal antibody cross-reactive to CSGVs engineered to contain the variable regions of the murine antibody on the backbone of human IgM. The chimeric IgM produced from the stably expressing HEK293 cell line was evaluated for use as a surrogate human-positive control in a serologic diagnostic test.

Geographical distribution and pathogenesis of ticks and tick-borne viral diseases

Ticks are obligatory hematophagous arthropods that harbor and transmit infectious pathogens to humans and animals. Tick species belonging to Amblyomma, Ixodes, Dermacentor, and Hyalomma genera may transmit certain viruses such as Bourbon virus (BRBV), Dhori virus (DHOV), Powassan virus (POWV), Omsk hemorrhagic fever virus (OHFV), Colorado tick fever virus (CTFV), Crimean-Congo hemorrhagic fever virus (CCHFV), Heartland virus (HRTV), Kyasanur forest disease virus (KFDV), etc. that affect humans and certain wildlife. The tick vectors may become infected through feeding on viraemic hosts before transmitting the pathogen to humans and animals. Therefore, it is vital to understand the eco-epidemiology of tick-borne viruses and their pathogenesis to optimize preventive measures. Thus this review summarizes knowledge on some medically important ticks and tick-borne viruses, including BRBV, POWV, OHFV, CTFV, CCHFV, HRTV, and KFDV. Further, we discuss these viruses' epidemiology, pathogenesis, and disease manifestations during infection.

Vaccine Preventable Disease Seroprevalence in a Nationwide Assessment of Timor-Leste (VASINA-TL): study protocol for a population-representative cross-sectional serosurvey

INTRODUCTION

Historic disruption in health infrastructure combined with data from a recent vaccine coverage survey suggests there are likely significant immunity gaps to vaccine preventable diseases and high risk of outbreaks in Timor-Leste. Community-based serological surveillance is an important tool to augment understanding of population-level immunity achieved through vaccine coverage and/or derived from prior infection.

METHODS AND ANALYSIS

This national population-representative serosurvey will take a three-stage cluster sample and aims to include 5600 individuals above 1 year of age. Serum samples will be collected by phlebotomy and analysed for measles IgG, rubella IgG, SARS-CoV-2 antispike protein IgG, hepatitis B surface antibody and hepatitis B core antigen using commercially available chemiluminescent immunoassays or ELISA. In addition to crude prevalence estimates and to account for differences in Timor-Leste's age structure, stratified age-standardised prevalence estimates will be calculated, using Asia in 2013 as the standard population. Additionally, this survey will derive a national asset of serum and dried blood spot samples which can be used for further investigation of infectious disease seroepidemiology and/or validation of existing and novel serological assays for infectious diseases.

ETHICS AND DISSEMINATION

Ethical approval has been obtained from the Research Ethics and Technical Committee of the Instituto Nacional da Saúde, Timor-Leste and the Human Research Ethics Committee of the Northern Territory Department of Health and Menzies School of Health Research, Australia. Co-designing this study with Timor-Leste's Ministry-of-Health and other relevant partner organisations will allow immediate translation of findings into public health policy, which may include changes to routine immunisation service delivery and/or plans for supplementary immunisation activities.

Human Seroprevalence for Dengue, Ross River, and Barmah Forest viruses in Australia and the Pacific: A systematic review spanning seven decades

Background

Dengue (DENV), Ross River (RRV) and Barmah Forest viruses (BFV) are the most common human arboviral infections in Australia and the Pacific Island Countries and Territories (PICTs) and are associated with debilitating symptoms. All are nationally notifiable in Australia, but routine surveillance is limited to a few locations in the PICTs. Understanding the level of human exposure to these viruses can inform disease management and mitigation strategies. To assess the historic and current seroprevalence of DENV, RRV and BFV in Australia and the PICTs we conducted a systematic literature review of all published quantitative serosurveys.

Methodology and principal findings

The Preferred Reporting of Items for Systematic Reviews and Meta-Analyses procedures were adopted to produce a protocol to systematically search for published studies reporting the seroprevalence of DENV, RRV and BFV in Australia and the PICTs. Data for author, research year, location, study population, serosurvey methods and positive tests were extracted. A total of 41 papers, reporting 78 serosurveys of DENV, RRV and BFV including 62,327 samples met the inclusion criteria for this review. Seroprevalence varied depending on the assay used, strategy of sample collection and location of the study population. Significant differences were observed in reported seropositivity depending on the sample collection strategy with clinically targeted sampling reporting the highest seroprevalence across all three viruses. Non-stratified seroprevalence showed wide ranges in reported positivity with DENV 0.0% – 95.6%, RRV 0.0% – 100.0%, and BFV 0.3% – 12.5%. We discuss some of the causes of variation including serological methods used, selection bias in sample collection including clinical or environmental associations, and location of study site. We consider the extent to which serosurveys reflect the epidemiology of the viruses and provide broad recommendations regarding the conduct and reporting of arbovirus serosurveys.

Conclusions and significance

Human serosurveys provide important information on the extent of human exposure to arboviruses across: (1) time, (2) place, and (3) person (e.g., age, gender, clinical presentation etc). Interpreting results obtained at these scales has the potential to inform us about transmission cycles, improve diagnostic surveillance, and mitigate future outbreaks. Future research should streamline methods and reduce bias to allow a better understanding of the burden of these diseases and the factors associated with seroprevalence. Greater consideration should be given to the interpretation of seroprevalence in studies, and increased rigour applied in linking seroprevalence to transmission dynamics.

Multiplex detection of antibodies to Chikungunya, O'nyong-nyong, Zika, Dengue, West Nile and Usutu viruses in diverse non-human primate species from Cameroon and the Democratic Republic of Congo

Background

Epidemic arbovirus transmission occurs among humans by mosquito bites and the sylvatic transmission cycles involving non-human primates (NHPs) still exists. However, limited data are available on the extent in NHPs infections and their role. In this study, we have developed and validated a high-throughput serological screening tool to study the circulation of multiple arboviruses that represent a significant threat to human health, in NHPs in Central Africa.

Methodology/Principal findings

Recombinant proteins NS1, envelope domain-3 (DIII) for the dengue (DENV), yellow fever (YFV), usutu (USUV), west nile (WNV) and zika (ZIKV) and envelope 2 for the chikungunya (CHIKV) and o'nyong-nyong (ONNV) were coupled to Luminex beads to detect IgG directed against these viruses. Evaluation of test performance was made using 161 human sera of known arboviral status (66 negative and 95 positive). The sensitivity and specificity of each antigen were determined by statistical methods and ROC curves (except for ONNV and USUV). All NS1 antigens (except NS1-YFV), CHIKV-E2 and WNV-DIII had sensitivities and specificities > 95%. For the other DIII antigens, the sensitivity was low, limiting the interest of their use for seroprevalence studies. Few simultaneous reactions were observed between the CHIKV+ samples and the NS1 antigens to the non-CHIKV arboviruses. On the other hand, the DENV+ samples crossed-reacted with NS1 of all the DENV serotypes (1 to 4), as well as with ZIKV, USUV and to a lesser extent with YFV. A total of 3,518 samples of 29 species of NHPs from Cameroon and the Democratic Republic of Congo (DRC) were tested against NS1 (except YFV), E2 (CHIKV/ONNV) and DIII (WNV) antigens. In monkeys (n = 2,100), the global prevalence varied between 2 and 5% for the ten antigens tested. When we stratified by monkey’s biotope, the arboreal species showed the highest reactivity. In monkeys from Cameroon, the highest IgG prevalence were observed against ONNV-E2 and DENV2-NS1 with 3.95% and 3.40% respectively and in DRC, ONNV-E2 (6.63%) and WNV-NS1 (4.42%). Overall prevalence was low in apes (n = 1,418): ranging from 0% for USUV-NS1 to 2.6% for CHIKV-E2. However, a very large disparity was observed among collection site and ape species, e.g. 18% (9/40) and 8.2% (4/49) of gorillas were reactive with CHIKV-E2 or WNV-NS1, respectively in two different sites in Cameroon.

Conclusions/Significance

We have developed a serological assay based on Luminex technology, with high specificity and sensitivity for simultaneous detection of antibodies to 10 antigens from 6 different arboviruses. This is the first study that evaluated on a large scale the presence of antibodies to arboviruses in NHPs to evaluate their role in sylvatic cycles. The overall low prevalence (<5%) in more than 3,500 NHPs samples from Cameroon and the DRC does not allow us to affirm that NHP are reservoirs, but rather, intermediate hosts of these viruses.

In the last decades, chikungunya, zika, yellow fever, usutu and dengue viruses have (re)-emerged in different parts of the world and many of these outbreaks occur in resource-limited countries with limited or under-equipped health facilities and where endemic malaria with very similar clinical symptoms confounds surveillance. Most arboviruses that circulate today likely originated in Africa where sporadic human outbreaks occur. In this work, we developed a serological tool that allows simultaneous detection of IgG antibodies to multiple arbovirus in a biological sample. With this highly sensitive and specific multiplex assay, we screened more than 3,500 samples collected from 29 species of monkeys and apes in Africa. We found a global IgG antibody prevalence of less than 5%. However, this seroprevalence varied by collection site, NPHs species and virus type. Given these findings, we concluded that African non-human primates are most likely not the reservoirs, but rather are intermediate hosts.

Comparison of Zika virus inactivation methods for reagent production and disinfection methods

Zika virus (ZIKV) infection remains a public health concern necessitating demand for long-term virus production for diagnostic assays and R&D activities. Inactivated virus constitutes an important component of the Trioplex rRT-PCR assay and serological IgM assay (MAC-ELISA). The aim of our study is to establish standard methods of ZIKV inactivation while maintaining antigenicity and RNA integrity. We tested viral supernatants by four different inactivation methods: 1. Heat inactivation at 56 °C and 60 °C; 2. Gamma-Irradiation; 3. Chemical inactivation by Beta-propiolactone (BPL) and 4. Fast-acting commercial disinfecting agents. Effectivity was measured by cytopathic effect (CPE) and plaque assay. RNA stability and antigenicity were measured by RT-PCR and MAC-ELISA, respectively. Results: Heat inactivation: Low titer samples, incubated at 56 °C for 2 h, showed neither CPE or plaques compared to high titer supernatants that required 2.5 h. Inactivation occurred at 60 °C for 60 min with all virus titers. Gamma irradiation: Samples irradiated at ≥3 Mrad for low virus concentrations and ≥5Mrad for high virus titer completely inactivated virus. Chemical Inactivation: Neither CPE nor plaques were observed with ≥0.045 % BPL inactivation of ZIKV. Disinfectant: Treatment of viral supernatants with Micro-Chem Plus™, inactivated virus in 2 min, whereas, Ethanol (70 %) and STERIS Coverage® Spray TB inactivated the virus in 5 min.

Development of diagnostic microsphere-based immunoassays for Heartland virus

BACKGROUND

Heartland virus (HRTV), a recently reclassified member of the genus Bandavirus, family Phenuiviridae, was first isolated in 2009 from a Missouri farmer exhibiting leukopenia and thrombocytopenia with suspected ehrlichiosis. Since then, more HRTV cases have been diagnosed, and firstline laboratory diagnostic assays are needed to identify future infections Objectives. We sought to develop rapid and reliable IgM and IgG microsphere immunoassays (MIAs) to test sera of patients suspected of having HRTV infection, and to distinguish between recent and past infections.

STUDY DESIGN

Heartland virus antigen was captured by an anti-HRTV monoclonal antibody covalently bound to microspheres. Antibodies in human sera from confirmed HRTV-positive and negative cases were reacted with the microsphere complexes and detected using a BioPlex® 200 instrument. Assay cutoffs were determined by receiver operator characteristic analysis of the normalized test output values, equivocal zones for each assay were defined, and sensitivities, specificities, accuracies, and imprecision values were calculated.

RESULTS

Sensitivities, specificities and accuracies of the IgM and IgG MIAs were all >95 %. Both tests were precise within and between assay plates, and cross-reactivity with other arboviruses was not observed.

CONCLUSIONS

HRTV IgM and IgG MIAs are accurate and rapid first-line methods to serologically identify recent and past HRTV infections.

Diagnostic Approach for Arboviral Infections in the United States

Domestic arthropod-borne viruses (arboviruses) are single-stranded RNA viruses, the most common of which include the mosquito-borne West Nile virus, St. Louis encephalitis virus, La Crosse virus, Jamestown Canyon virus, and eastern equine encephalitis virus, as well as the tick-borne Powassan virus. Previously considered rare infections, they have been detected with increasing frequency over the past 2 decades. Here, we present an overview of the domestic arboviruses listed above and describe the modalities employed to diagnose infection. Global arboviruses, including dengue virus, Zika virus, and chikungunya virus, have also been increasingly detected in the United States within the last 5 years but are not a focus of this minireview. Typical manifestations of arbovirus infection range from no symptoms, to meningitis or encephalitis, to death. Serologies are the standard means of diagnosis in the laboratory, since most viruses have a short period of replication, limiting the utility of molecular tests. The interpretation of serologies is confounded by antibody cross-reactivity with viruses belonging to the same serogroup and by long-lasting antibodies from prior infections. Next-generation assays have improved performance by increasing antigen purity, selecting optimal epitopes, and improving interpretive algorithms, but challenges remain. Due to cross-reactivity, a positive first-line serology test requires confirmation by either a plaque reduction neutralization test or detection of seroconversion or a 4-fold rise in virus-specific IgM or IgG antibody titers from acute- and convalescent-phase sera. The use of molecular diagnostics, such as reverse transcription PCR or unbiased metagenomic sequencing, is limited to the minority of patients who present with ongoing viremia or central nervous system replication. With the continued expansion of vector range, the diagnosis of domestic arboviruses will become an increasingly important task for generalists and specialists alike.

Evaluation for Arboviral Infection Among Children Hospitalized in Colorado With Aseptic Meningitis and Encephalitis

Among 39 children hospitalized in Colorado with aseptic meningitis or encephalitis, 16 (41%) had an etiology identified, including 2 (5%) with West Nile virus infection. Despite extensive testing, no other arboviral infections were identified. Arboviral infection should be considered in children with neuroinvasive disease during arboviral season with testing directed toward viruses endemic to the region and type of exposure.

Development of a multiplex microsphere immunoassay for the detection of antibodies against highly pathogenic viruses in human and animal serum samples

Surveillance of highly pathogenic viruses circulating in both human and animal populations is crucial to unveil endemic infections and potential zoonotic reservoirs. Monitoring the burden of disease by serological assay could be used as an early warning system for imminent outbreaks as an increased seroprevalance often precedes larger outbreaks. However, the multitude of highly pathogenic viruses necessitates the need to identify specific antibodies against several targets from both humans as well as from potential reservoir animals such as bats. In order to address this, we have developed a broadly reactive multiplex microsphere immunoassay (MMIA) for the detection of antibodies against several highly pathogenic viruses from both humans and animals. To this aim, nucleoproteins (NP) of Ebola virus (EBOV), Marburg virus (MARV) and nucleocapsid proteins (NP) of Crimean-Congo haemorrhagic fever virus, Rift Valley fever virus and Dobrava-Belgrade hantavirus were employed in a 5-plex assay for IgG detection. After optimisation, specific binding to each respective NP was shown by testing sera from humans and non-human primates with known infection status. The usefulness of our assay for serosurveillance was shown by determining the immune response against the NP antigens in a panel of 129 human serum samples collected in Guinea between 2011 and 2012 in comparison to a panel of 88 sera from the German blood bank. We found good agreement between our MMIA and commercial or in-house reference methods by ELISA or IIFT with statistically significant higher binding to both EBOV NP and MARV NP coupled microspheres in the Guinea panel. Finally, the MMIA was successfully adapted to detect antibodies from bats that had been inoculated with EBOV- and MARV- virus-like particles, highlighting the versatility of this technique and potentially enabling the monitoring of wildlife as well as human populations with this assay. We were thus able to develop and validate a sensitive and broadly reactive high-throughput serological assay which could be used as a screening tool to detect antibodies against several highly pathogenic viruses.

Improved Detection of Antibodies against SARS-CoV-2 by Microsphere-Based Antibody Assay

Currently available COVID-19 antibody tests using enzyme immunoassay (EIA) or immunochromatographic assay have variable sensitivity and specificity. Here, we developed and evaluated a novel microsphere-based antibody assay (MBA) for detecting immunoglobulin G (IgG) against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) nucleoprotein (NP) and spike protein receptor binding domain (RBD). The seropositive cutoff value was set using a cohort of 294 anonymous serum specimens collected in 2018. The specificity was assessed using serum specimens collected from organ donors or influenza patients before 2020. Seropositive rate was determined among COVID-19 patients. Time-to-seropositivity and signal-to-cutoff (S/CO) ratio were compared between MBA and EIA. MBA had a specificity of 100% (93/93; 95% confidence interval (CI), 96-100%) for anti-NP IgG, 98.9% (92/93; 95% CI 94.2-100%) for anti-RBD IgG. The MBA seropositive rate for convalescent COVID-19 patients was 89.8% (35/39) for anti-NP IgG and 79.5% (31/39) for anti-RBD IgG. The time-to-seropositivity was shorter with MBA than EIA. MBA could better differentiate between COVID-19 patients and negative controls with higher S/CO ratio for COVID-19 patients, lower S/CO ratio with negative controls and fewer specimens in the equivocal range. MBA is robust, simple and is suitable for clinical microbiology laboratory for the accurate determination of anti-SARS-CoV-2 antibodies for diagnosis, serosurveillance, and vaccine trials.

Serological Diagnosis of Flavivirus-Associated Human Infections

Arthropod-borne viruses (arboviruses) belonging to the Flavivirus genus of the Flaviviridae family, are a major public health threat in tropical and subtropical regions, and have recently become a medical concern in temperate zones. Most flaviviruses are classified as zoonotic viruses. Human flavivirus infections can be asymptomatic, responsible for unspecific symptoms in the first few days following infection, or responsible for severe complications potentially resulting in death. During the first days following symptom onset, laboratory diagnosis of acute human flavivirus infection is mainly based on molecular detection of the viral genome by RT-PCR methods, followed by the capture of specific antibodies using serological tests after the first week of infection. The detection of antibodies that have virus neutralizing activity can be used to confirm flavivirus infection. However, human flavivirus infections induce the production of cross-reactive antibodies, often making serology inconclusive. Indeed, serological diagnosis of flavivirus infection can be hampered by a patient's history of flavivirus exposure, particularly in regions where multiple antigenically related flaviviruses co-circulate. We focus our mini review on conventional immunoassays that allow the diagnosis of major flavivirus-associated human infections in basic, routine and high-profile central health centers; and the interpretation of diagnostic serology tests for patients living within different epidemiological situations.

Optimisation and standardisation of a multiplex immunoassay of diverse Plasmodium falciparum antigens to assess changes in malaria transmission using sero-epidemiology

Background: Antibody responses have been used to characterise transmission and exposure history in malaria-endemic settings for over a decade. Such studies have typically been conducted on well-standardised enzyme-linked immunosorbent assays (ELISAs). However, recently developed quantitative suspension array technologies (qSAT) are now capable of high-throughput and multiplexed screening of up to hundreds of analytes at a time. This study presents a customised protocol for the Luminex MAGPIX © qSAT using a diverse set of malaria antigens. The aim is to develop a standardised assay for routine serological surveillance that is implementable across laboratories and epidemiological settings. Methods: A panel of eight Plasmodium falciparum recombinant antigens, associated with long- and short-lived antibody responses, was designed for the Luminex MAGPIX © platform. The assay was optimised for key steps in the protocol: antigen-bead coupling concentration, buffer composition, serum sample dilution, and bead storage conditions. Quality control procedures and data normalisation methods were developed to address high-throughput assay processing.  Antigen-specific limits of quantification (LOQs) were also estimated using both in-house and WHO reference serum as positive controls. Results: Antigen-specific bead coupling was optimised across five serum dilutions and two positive controls, resulting in concentrations operational within stable analytical ranges. Coupled beads were stable after storage at room temperature (22⁰C) for up to eight weeks. High sensitivity and specificity for distinguishing positive and negative controls at serum sample dilutions of 1:500 (AUC 0.94 95%CI 0.91-0.96) and 1:1000 (AUC 0.96 95%CI 0.94-0.98) were observed. LOQs were also successfully estimated for all analytes but varied by antigen and positive control. Conclusions: This study demonstrates that developing a standardised malaria-specific qSAT protocol for a diverse set of antigens is achievable, though further optimisations may be required. Quality control and data standardisation methods may also be useful for future analysis of large sero-epidemiological surveys.

Optimisation and standardisation of a multiplex immunoassay of diverse Plasmodium falciparum antigens to assess changes in malaria transmission using sero-epidemiology

Background: Antibody responses have been used to characterise transmission and exposure history in malaria-endemic settings for over a decade. Such studies have typically been conducted on well-standardised enzyme-linked immunosorbent assays (ELISAs). However, recently developed quantitative suspension array technologies (qSAT) are now capable of high-throughput and multiplexed screening of up to hundreds of analytes at a time. This study presents a customised protocol for the Luminex MAGPIX ^© qSAT using a diverse set of malaria antigens. The aim is to develop a standardised assay for routine serological surveillance that is implementable across laboratories and epidemiological settings.

Methods: A panel of eight Plasmodium falciparum recombinant antigens, associated with long- and short-lived antibody responses, was designed for the Luminex MAGPIX ^© platform. The assay was optimised for key steps in the protocol: antigen-bead coupling concentration, buffer composition, serum sample dilution, and bead storage conditions. Quality control procedures and data normalisation methods were developed to address high-throughput assay processing.  Antigen-specific limits of quantification (LOQs) were also estimated using both in-house and WHO reference serum as positive controls.

Results: Antigen-specific bead coupling was optimised across five serum dilutions and two positive controls, resulting in concentrations operational within stable analytical ranges. Coupled beads were stable after storage at room temperature (22⁰C) for up to eight weeks. High sensitivity and specificity for distinguishing positive and negative controls at serum sample dilutions of 1:500 (AUC 0.94 95%CI 0.91-0.96) and 1:1000 (AUC 0.96 95%CI 0.94-0.98) were observed. LOQs were also successfully estimated for all analytes but varied by antigen and positive control.

Conclusions: This study demonstrates that developing a standardised malaria-specific qSAT protocol for a diverse set of antigens is achievable, though further optimisations may be required. Quality control and data standardisation methods may also be useful for future analysis of large sero-epidemiological surveys.

Development of a bead-based immunoassay using virus-like particles for detection of alphaviral humoral response

There is a pressing need for sustainable and sensitive immunodiagnostics for use in public health efforts to understand and combat the threat of endemic and emerging infectious diseases. In this proof-of-concept work, we describe an immunodiagnostic approach based on the utilization of virus-like particles (VLPs) in a magnetic bead-based platform for multiplexed detection of antiviral humoral response. A retroviral-based VLP, that presents Venezuelan equine encephalitis virus E1/E2 glycoprotein antigen on its surface, was synthesized and coupled to magnetic beads to create VLP-conjugated microspheres (VCMs). Using these VCMs, IgM and IgG antibodies were detectable in nonhuman primate (NHP) and human clinical serum samples at dilutions of 1 × 10 Basile et al. [4] and greater. We also extended the VCM methodology to an Old World alphavirus, chikungunya virus, demonstrating the flexibility of this approach toward different VLP architectures. When multiplexed on the MAGPIX® platform, this method provided differential detection between Old World and New World alphaviral IgM. This flexible, immunodiagnostic method, based on the MAGPIX® platform, demonstrates compatibility of particulate antigens with bead-based assays, improves sensitivity by up to 2-logs, and has faster sample-to-answer time over traditional methods.

Development and Evaluation of a Multiplexed Immunoassay for Simultaneous Detection of Serum IgG Antibodies to Six Human Coronaviruses

Known human coronaviruses (hCoV) usually cause mild to moderate upper-respiratory tract illnesses, except SARS-CoV and MERS-CoV, which, in addition to mild illness can also be associated with severe respiratory diseases and high mortality rates. Well-characterized multiplexed serologic assays are needed to aid in rapid detection and surveillance of hCoVs. The present study describes development and evaluation of a multiplexed magnetic microsphere immunoassay (MMIA) to simultaneously detect immunoglobulin G (IgG) antibodies specific for recombinant nucleocapsid proteins (recN) from hCoVs 229E, NL63, OC43, HKU1, SARS-CoV, and MERS-CoV. We used paired human sera to screen for IgG with reactivity against six hCoVs to determine assay sensitivity, specificity and reproducibility. We found no signal interference between monoplex and multiplex assay formats (R² range = 0.87–0.97). Screening of paired human sera using MMIA, resulted in 92 of 106 (sensitivity: 86%) as positive and 68 of 80 (specificity: 84%) as negative. This study serves as a proof of concept that it is feasible to develop and use a multiplexed microsphere immunoassay as a next generation screening tool for use in large scale seroprevalence studies of hCoVs.

Development and validation of magnetic bead pentaplex immunoassay for simultaneous quantification of murine serum IgG antibodies to acellular pertussis, diphtheria and tetanus antigens used in combination vaccines

We describe here a magnetic bead-based multiplex (pentaplex) immunoassay (MIA) platform developed as an alternative to enzyme-linked immunosorbent assays (ELISA) used in immunogenicity testing of DTaP/TdaP vaccine in animals. MIA simultaneously measures the concentration of serum (IgG) antibodies against B. Pertussis antigens; pertussis toxin, filamentous hemagglutinin (FHA), pertactin (PRN) and tetanus (T) and diphtheria (D) toxoid in the Tdap vaccine immunized animals. Assay validation experiments were done using a panel of serum samples. The results are expressed in IU/ml using WHO reference mice serum. The standard curve was linear with 4PL logistic fit over an eight 2-fold dilution range with LOQ of 0.003, 0.022, 0.005 IU/ml for PT, FHA and PRN and 0.016 U/ml for T and D antigens indicating sensitivity. No interference was observed in monoplex versus multiplex measurements. Specificity was demonstrated by ≥90% homologous and ≤15% heterologous inhibition for all the antigens. The assay was reproducible, with a mean coefficient of variation (CV) of ≤10% for intra-assay duplicates and ≤25% for interassays using different lots of beads and analyst. Accuracy was demonstrated wherein the ratio of observed vs. assigned unitages were within 80-120%. The study suggests that the Pentaplex (MIA) platform meets all the criteria for the serological assay combination vaccines with additional advantages of high throughput, reduced sample volumes, faster analysis with reduced manpower in contrast to conventional monoplex ELISA.

Tick-Borne Flaviviruses, with a Focus on Powassan Virus

The tick-borne pathogen Powassan virus is a rare cause of encephalitis in North America and the Russian Far East. The number of documented cases described since the discovery of Powassan virus in 1958 may be <150, although detection of cases has increased over the past decade. In the United States, the incidence of Powassan virus infections expanded from the estimated 1 case per year prior to 2005 to 10 cases per year during the subsequent decade. The increased detection rate may be associated with several factors, including enhanced surveillance, the availability of improved laboratory diagnostic methods, the expansion of the vector population, and, perhaps, altered human activities that lead to more exposure. Nonetheless, it remains unclear whether Powassan virus is indeed an emerging threat or if enzootic cycles in nature remain more-or-less stable with periodic fluctuations of host and vector population sizes. Despite the low disease incidence, the approximately 10% to 15% case fatality rate of neuroinvasive Powassan virus infection and the temporary or prolonged sequelae in >50% of survivors make Powassan virus a medical concern requiring the attention of public health authorities and clinicians. The medical importance of Powassan virus justifies more research on developing specific and effective treatments and prevention and control measures.

Yellow fever in the diagnostics laboratory

Yellow fever (YF) remains a public health issue in endemic areas despite the availability of a safe and effective vaccine. In 2015–2016, urban outbreaks of YF were declared in Angola and the Democratic Republic of Congo, and a sylvatic outbreak has been ongoing in Brazil since December 2016. Of great concern is the risk of urban transmission cycles taking hold in Brazil and the possible spread to countries with susceptible populations and competent vectors. Vaccination remains the cornerstone of an outbreak response, but a low vaccine stockpile has forced a sparing-dose strategy, which has thus far been implemented in affected African countries and now in Brazil. Accurate laboratory confirmation of cases is critical for efficient outbreak control. A dearth of validated commercial assays for YF, however, and the shortcomings of serological methods make it challenging to implement YF diagnostics outside of reference laboratories. We examine the advantages and drawbacks of existing assays to identify the barriers to timely and efficient laboratory diagnosis. We stress the need to develop new diagnostic tools to meet current challenges in the fight against YF.

Detection of Specific ZIKV IgM in Travelers Using a Multiplexed Flavivirus Microsphere Immunoassay

Zika virus (ZIKV) has spread widely in the Pacific and recently throughout the Americas. Unless detected by RT-PCR, confirming an acute ZIKV infection can be challenging. We developed and validated a multiplexed flavivirus immunoglobulin M (IgM) microsphere immunoassay (flaviMIA) which can differentiate ZIKV-specific IgM from that due to other flavivirus infections in humans. The flaviMIA bound 12 inactivated flavivirus antigens, including those from ZIKV and yellow fever virus (YFV), to distinct anti-flavivirus antibody coupled beads. These beads were used to interrogate sera from patients with suspected ZIKV infection following travel to relevant countries. FlaviMIA results were validated by comparison to the ZIKV plaque reduction neutralization test (PRNT). The results highlight the complexity of serological ZIKV diagnosis, particularly in patients previously exposed to, or vaccinated against, other flaviviruses. We confirmed 99 patients with ZIKV infection by a combination of RT-PCR and serology. Importantly, ZIKV antibodies could be discriminated from those ascribed to other flavivirus infections. Serological results were sometimes confounded by the presence of pre-existing antibodies attributed to previous flavivirus infection or vaccination. Where RT-PCR results were negative, testing of appropriately timed paired sera was necessary to demonstrate seroconversion or differentiation of recent from past infection with or exposure to ZIKV.

Development of quantitative suspension array assays for six immunoglobulin isotypes and subclasses to multiple Plasmodium falciparum antigens

BACKGROUND

Quantitative suspension arrays are powerful immunoassays to measure antibodies against multiple antigens in large numbers of samples in a short time and using few microliters. To identify antigen targets of immunity for vaccine development against complex microbes like Plasmodium falciparum, such technology allows the characterization of the magnitude and antigenic specificity of Ig isotypes and subclasses that are important for functional responses. However, standardized assays are not widely available.

METHODS

We developed six quantitative suspension array assays to measure IgG1, IgG2, IgG3, IgG4, IgM and IgE specific to multiple P. falciparum antigens. Secondary and tertiary antibodies, as well as human purified antibodies for standard curves, were tested among several commercially available sources. Positive and negative controls included plasmas from malaria hyper-immune African adults and from malaria-naïve European adults, respectively. Reagents were selected and optimal antibody and test sample dilutions established according to sensitivity, specificity and performance of the standard curves. The variability between replicates and plates was assessed with 30 test samples and controls.

RESULTS

Assays were able to detect P. falciparum antigen-specific antibodies for all isotypes and subclasses in samples from malaria-exposed individuals, with low background signal in blank wells. Levels detected in malaria-naïve individuals were overall low except for IgM. For the IgG2 and IgE assays, a triple sandwich was required for sensitivity. Standard curves with 5-parameter logistic fit were successfully obtained in all assays. The coefficients of variation for measurements performed in different days were all <30%, and <5% when comparing duplicates from the same plate.

CONCLUSION

The isotype/subclass assays developed here were sensitive, specific, reproducible and of adequate quantification dynamic range. They allow performing detailed immuno-profiling to large panels of P. falciparum antigens to address naturally- and vaccine-induced Ig responses and elucidate correlates of malaria protection, and could also be applied to other antigenic panels.

Advances in Diagnosis, Surveillance, and Monitoring of Zika Virus: An Update

Zika virus (ZIKV) is associated with numerous human health-related disorders, including fetal microcephaly, neurological signs, and autoimmune disorders such as Guillain-Barré syndrome (GBS). Perceiving the ZIKA associated losses, in 2016, the World Health Organization (WHO) declared it as a global public health emergency. In consequence, an upsurge in the research on ZIKV was seen around the globe, with significant attainments over developing several effective diagnostics, drugs, therapies, and vaccines countering this life-threatening virus at an early step. State-of-art tools developed led the researchers to explore virus at the molecular level, and in-depth epidemiological investigations to understand the reason for increased pathogenicity and different clinical manifestations. These days, ZIKV infection is diagnosed based on clinical manifestations, along with serological and molecular detection tools. As, isolation of ZIKV is a tedious task; molecular assays such as reverse transcription-polymerase chain reaction (RT-PCR), real-time qRT-PCR, loop-mediated isothermal amplification (LAMP), lateral flow assays (LFAs), biosensors, nucleic acid sequence-based amplification (NASBA) tests, strand invasion-based amplification tests and immune assays like enzyme-linked immunosorbent assay (ELISA) are in-use to ascertain the ZIKV infection or Zika fever. Herein, this review highlights the recent advances in the diagnosis, surveillance, and monitoring of ZIKV. These new insights gained from the recent advances can aid in the rapid and definitive detection of this virus and/or Zika fever. The summarized information will aid the strategies to design and adopt effective prevention and control strategies to counter this viral pathogen of great public health concern.

Diagnosis of Viral Infections

Accurate diagnosis of viral infections enhances the ability of the clinician to make decisions on appropriate treatment of patients, evaluate disease progression and prevent misuse of antibiotics. Knowledge of the pathogen involved also allow implementation of infection control and monitoring of success of antiviral treatments that may affect the prognosis of patients. Epidemiological data collected through accurate diagnostics play an important role in public health through identification and control of outbreaks, implementation of appropriate diagnostic tests, vaccination programs and treatment but also to recognize common and emerging pathogens in a community. It is key that the clinician have an understanding of appropriate specimens to send to the laboratory and the value of specific nucleic acid and serological testing for different viral pathogens. Molecular techniques have revolutionized viral diagnoses over the past decade and enhanced both the sensitivity and specificity of tests and the speed by which a diagnosis can be made and new tests be developed. The continued use of serology for viruses with a short viremia, or for chronic infections should however complement these tests. This chapter aims to provide an overview of the available tests, the principles of testing and appropriate tests to select for different viruses and syndromes. Also provided is a glimpse of new developments in diagnostics that may further enhance the capacity to make a conclusive diagnosis in the near future.

Mayaro virus: a forest virus primed for a trip to the city?

Mayaro virus (MAYV) is an emerging arthropod-borne virus (arbovirus). Infection by MAYV can produce Mayaro virus disease (MAYVD) which is usually a clinically diagnosed, acute, febrile illness associated with prolonged and painful joint inflammation and swelling. MAYVD may be clinically indistinguishable from dengue, chikungunya fever, malaria, rabies, measles or other arboviral diseases. The full spectrum of disease, sequelae, routes of infection, virus shedding and any rarer means of transmission remain undefined. MAYVD cases in humans have so far been localised to Central and South America, particularly regions in and around the Amazon basin. MAYV usually circulates in a sylvan cycle of forest mosquitoes and vertebrates, however it has also been found in more urban locations alongside anthropophilic (preferring humans) insect vectors. If transmission via anthropophilic mosquitoes becomes more efficient following viral change, or existing vectors change their habitat and biting habits, the risk of urban establishment and further spread into non-forested areas will grow. Surveillance, testing and vector control remain key to monitoring and preventing global spread and establishment. The possibility of MAYV becoming further urbanized is worthy of note, consideration and action to ensure MAYV does not spread beyond the forests and establish in the world's cities.

Production of a Sindbis/Eastern Equine Encephalitis chimeric virus inactivated cell culture antigen

Eastern Equine Encephalitis virus (EEEV) is a medically important pathogen that can cause severe encephalitis in humans, with mortality rates ranging from 30 to 80%. Unfortunately there are no antivirals or licensed vaccines available for human use, and laboratory diagnosis is essential to differentiate EEEV infection from other pathogens with similar clinical manifestations. The Arboviral Diseases Branch (ADB) reference laboratory at the CDC Division of Vector-Borne Diseases (DVBD) produces reference antigens used in serological assays such as the EEEV immunoglobulin M antibody-capture enzyme-linked immunosorbent assay (MAC-ELISA). However, EEEV is classified as a HHS select agent and requires biosafety level (BSL) three containment, limiting EEEV antigen production in non-select agent and BSL-2 laboratories. A recombinant Sindbis virus (SINV)/EEEV has been constructed for use under BSL-2 conditions and is not regulated as a select agent. Cell culture production of inactivated EEEV antigen from SINV/EEEV for use in the EEEV MAC-ELISA is reported here. Cell culture conditions and inactivation procedures were analyzed for SINV/EEEV using a recently developed antigen production algorithm, with the MAC-ELISA as the performance indicator.

Dengue laboratory diagnosis: still some room for improvement

Dengue is the most important and widely distributed arthropod-borne viral disease affecting humans. The number of dengue virus infections has steadily grown and more than 100 countries survey dengue incidence every year. Due to the lack of an approved antiviral treatment or licensed preventative vaccine, accurate and opportune diagnosis is commended for efficient dengue epidemiological surveillance, to propose control measures in order to curtail outbreaks timely and treat patients satisfactorily. In this review, the basis, application and indications for different diagnostic tests are described, and their advantages and limitations considered. At the end of this piece, we speculate what the future may hold for the diagnosis of dengue infections.

Rodents and risk in the Mekong Delta of Vietnam: seroprevalence of selected zoonotic viruses in rodents and humans

In the Mekong Delta in southern Vietnam, rats are commonly traded in wet markets and sold live for food consumption. We investigated seroprevalence to selected groups of rodent-borne viruses among human populations with high levels of animal exposure and among co-located rodent populations. The indirect fluorescence antibody test (IFAT) was used to determine seropositivity to representative reference strains of hantaviruses (Dobrava virus [DOBV], Seoul virus [SEOV]), cowpox virus, arenaviruses (lymphocytic choriomeningitis virus [LCMV]), flaviviruses (tick-borne encephalitis virus [TBEV]), and rodent parechoviruses (Ljungan virus), using sera from 245 humans living in Dong Thap Province and 275 rodents representing the five common rodent species sold in wet markets and present in peridomestic and farm settings. Combined seropositivity to DOBV and SEOV among the rodents and humans was 6.9% (19/275) and 3.7% (9/245), respectively; 1.1% (3/275) and 4.5% (11/245) to cowpox virus; 5.4% (15/275) and 47.3% (116/245) for TBEV; and exposure to Ljungan virus was 18.8% (46/245) in humans, but 0% in rodents. Very little seroreactivity was observed to LCMV in either rodents (1/275, 0.4%) or humans (2/245, 0.8%). Molecular screening of rodent liver tissues using consensus primers for flaviviruses did not yield any amplicons, whereas molecular screening of rodent lung tissues for hantavirus yielded one hantavirus sequence (SEOV). In summary, these results indicate low to moderate levels of endemic hantavirus circulation, possible circulation of a flavivirus in rodent reservoirs, and the first available data on human exposures to parechoviruses in Vietnam. Although the current evidence suggests only limited exposure of humans to known rodent-borne diseases, further research is warranted to assess public health implications of the rodent trade.