Detection of human anti-flavivirus antibodies with a west nile virus recombinant antigen microsphere immunoassay

Development of a novel serological assay for the detection of mpox infection in vaccinated populations

In 2022 the World Health Organization declared a Public Health Emergency for an outbreak of mpox, the zoonotic Orthopoxvirus (OPV) affecting at least 104 nonendemic locations worldwide. Serologic detection of mpox infection is problematic, however, due to considerable antigenic and serologic cross-reactivity among OPVs and smallpox-vaccinated individuals. In this report, we developed a high-throughput multiplex microsphere immunoassay using a combination of mpox-specific peptides and cross-reactive OPV proteins that results in the specific serologic detection of mpox infection with 93% sensitivity and 98% specificity. The New York State Non-Vaccinia Orthopoxvirus Microsphere Immunoassay is an important tool to detect subclinical mpox infection and understand the extent of mpox spread in the community through retrospective analysis.

Duration of Seroprotection of the live attenuated SA-14-14-2 Japanese encephalitis vaccine in children in India

BACKGROUND

Acute encephalitis syndrome (AES) is a major public health concern in India and the Japanese Encephalitis (JE) Virus is the most common cause of viral encephalitis in Asia affecting children under the age of 15 years. In India, despite the introduction of the JE vaccine (SA-14-14-2) in the immunization programme, JE continues to account for 15-20% of AES cases to date. The present study evaluates the immunogenicity of live attenuated SA-14-14-2 JE vaccine in terms of persistence of the humoral response after two doses.

METHODS

A cross-sectional study was conducted among 266 children belonging to one of the JE endemic regions of Uttar Pradesh, India. Blood samples were taken from children (2-10 years) and grouped according to the duration (in years) after two doses of the vaccine (five groups with a class interval of two years). Informed written consent was obtained from the parents/guardians. All the samples collected were tested for the presence of anti-JEV-specific IgG antibodies by enzyme-linked immunosorbent assay (ELISA) and further confirmed by micro neutralization test (MNT) and immunofluorescence assays.

RESULTS

Of the 266 samples tested by ELISA for anti-JEV-specific IgG antibodies, 260 (97.74%) were negative and six (2.26%) were equivocal. The geometric mean immune status ratio across the five groups, 0-2 years (n = 59), 2-4 years (n = 73), 4-6 years (n = 65), 6-8 years (n = 48) and 8-10 years (n = 21) post two doses of SA-14-14-2 JE vaccine was 1.143, 1.059, 1.138, 1.075 and 1.130 respectively and the geometric mean titre (GMT) obtained from MNT across the five groups were 10.77, 8.400, 8.453, 9.517 and 9.674 respectively.

CONCLUSION

The study showed a decreasing trend of anti-JEV specific IgG antibody titers across the five groups based on the duration following two doses of SA-14-14-2 vaccine. The results emphasize the significance of booster doses of vaccine for children living in endemic areas.

High-Throughput Multiplex SARS-CoV-2 IgG Microsphere Immunoassay for Dried Blood Spots: A Public Health Strategy for Enhanced Serosurvey Capacity

Early in the pandemic when diagnostic testing was not widely available, serosurveys played an important role in estimating the prevalence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in different populations. Dried blood spots (DBS), which can be collected in nonclinical settings, provide a minimally invasive alternative to serum for serosurveys. We developed a Luminex-based SARS-CoV-2 microsphere immunoassay (MIA) for DBS that detects IgG antibodies to nucleocapsid (N) and spike subunit 1 (S1) antigens. The assay uses a 384-well plate format and automated liquid handlers for high-throughput capacity. Specificity was assessed using a large collection of prepandemic DBS and well-characterized sera. Sensitivity was analyzed using serology data from New York State SARS-CoV-2 serosurvey testing and matched diagnostic test results. For DBS, the specificity was 99.5% for the individual N and S1 antigens. Median fluorescence intensity (MFI) values for DBS and paired sera showed a strong positive correlation for N (R2 = 0.91) and S1 (R2 = 0.93). Sensitivity, assessed from 1,134 DBS with prior laboratory-confirmed SARS-CoV-2 infection, ranged from 83% at 0 to 20 days to 95% at 61 to 90 days after a positive test. When stratified using coronavirus disease 2019 (COVID-19) symptom data, sensitivity ranged from 90 to 96% for symptomatic and 77 to 91% for asymptomatic individuals. For 8,367 health care workers reporting detailed symptom data, MFI values were significantly higher for all symptom categories. Our results indicate that the SARS-CoV-2 IgG DBS MIA is sensitive, specific, and well-suited for large population-based serosurveys. The ability to readily modify and multiplex antigens is important for ongoing assessment of SARS-CoV-2 antibody responses to emerging variants and vaccines. IMPORTANCE Testing for antibodies to SARS-CoV-2 has been used to estimate the prevalence of COVID-19 in different populations. Seroprevalence studies, or serosurveys, were especially useful during the early phase of the pandemic when diagnostic testing was not widely available, and the resulting seroprevalence estimates played an important role in public health decision making. To achieve meaningful results, antibody tests used for serosurveys should be accurate and accessible to diverse populations. We developed a test that detects antibodies to two different SARS-CoV-2 proteins in dried blood spots (DBS). DBS require only a simple fingerstick and can be collected in nonclinical settings. We conducted a robust validation study and have demonstrated that our test is both sensitive and specific. Furthermore, we demonstrated that our test is suitable for large-scale serosurveys by testing over 56,000 DBS collected in a variety of community-based venues in New York State during the spring of 2020.

Development and Evaluation of Real-Time Reverse Transcription Recombinase Polymerase Amplification Assay for Rapid and Sensitive Detection of West Nile Virus in Human Clinical Samples

West Nile virus (WNV) causes West Nile fever and encephalitis worldwide. Currently, there are no effective drugs or vaccines available in the market to treat WNV infection in humans. Hence, it is of paramount importance to detect WNV early for the success of the disease control programs and timely clinical management in endemic areas. In the present paper, we report the development of real-time reverse transcription recombinase polymerase amplification (RT-RPA) assay for rapid and real-time detection of WNV targeting the envelope (env) gene of the virus. The RPA reaction was performed successfully at 39°C for 15 min in a real-time thermal cycler. The sensitivity of this assay was found similar to that of the quantitative real-time RT PCR (RT-qPCR) assay, which could detect 10 copies of the gene. The efficacy of the assay was evaluated with a panel of 110 WN suspected human samples showing the signs of retinitis, febrile illness and acute posterior uveitis. In comparison with RT-qPCR, RT-RPA showed a specificity of 100% (CI, 95.07–100%) and sensitivity of 96.15% (CI, 80.36–99.90%) with a negative (NPV) and positive predictive value (PPV) of 98.65 and 100%, respectively. The level of agreement between RT-RPA and reference RT-qPCR assay was shown to be very high. The turnaround time of real-time RPA assay is about 10-20 times faster than the RT-qPCR, which confirms its utility in the rapid and sensitive diagnosis of WNV infection. To the best of our knowledge, this is the first report which deals with the development of real-time RT-RPA assay for simple, rapid, sensitive, and specific detection of WNV in human clinical samples. The present RT-RPA assay proves to be a powerful tool that can be used for the rapid diagnosis of a large number of patient samples in endemic settings.

Evaluation of a commercially-available surrogate virus neutralization test for severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2)

There remains an urgent need for assays to quantify humoral protective immunity to SARS-CoV-2 to understand the immune responses of COVID-19 patients, evaluate efficacy of vaccine candidates in clinical trials, and conduct large-scale epidemiological studies. The plaque-reduction neutralization test (PRNT) is the reference-standard for quantifying antibodies capable of neutralizing SARS-CoV-2. However, the PRNT is logistically demanding, time-consuming, and requires containment level-3 facilities to safely work with live virus. In contrast, a surrogate virus neutralization test (sVNT) manufactured by Genscript is a quick and simple assay that detects antibodies that inhibit the RBD-ACE2 interaction, crucial for virus entry into host cells. In this study, we evaluate the sensitivity, specificity, and cross-reactivity of the sVNT compared with the PRNT using both 50% and 90% SARS-CoV-2 neutralization as a reference-standard. We found that the sVNT provides a high-throughput screening tool prior to confirmatory PRNT testing for the evaluation of SARS-CoV-2 neutralizing antibodies.

Serosurvey for dengue virus infection among pregnant women in the West Nile virus enzootic community of El Paso Texas

All 4 dengue viruses (DENV) cause sporadic outbreaks of human disease in the Rio Grande Valley along the US-Mexico border. In addition, West Nile virus (WNV) is enzootic in most border communities, and is the only arbovirus known to cause human disease in the El Paso, Texas community. In an effort to determine if DENV were also endemic in the El Paso community, a serosurvey was conducted among mothers at the time of delivery of their babies in selected hospitals. Cord-blood plasma samples obtained from mothers were tested for DENV antibody by an enzyme-linked immuno-sorbent assay (ELISA), plaque reduction neutralization test (PRNT) and a multiplex microsphere immunoassay. All DENV antibody positive plasma samples were also tested for WNV antibody by the same assays to consider the possibility that DENV antibody positive samples reflected WNV cross reactive antibody. The results indicated that 0.74% (11/1,472) of the mothers had a previous DENV infection and that 3.3% (48/1,472) had a previous WNV infection. Of these mothers, 0.20% (3/1,472) had antibody to both DENV and WNV as evidence of infection by both viruses. The results indicated that 0.2% (3/1472) of the mothers were positive for antibody to only WNV envelope, thus suggesting an undetermined flavivirus infection. Although 6 of the 11 DENV antibody positive mothers did not have a history of travel to a DENV endemic country, the findings of this survey provided further evidence of local transmission of WNV and suggested the possibility of focal autochthonous transmission of DENV in the El Paso community.

CoVaccine HT™ Adjuvant Potentiates Robust Immune Responses to Recombinant SARS-CoV-2 Spike S1 Immunization

The current COVID-19 pandemic has claimed hundreds of thousands of lives and its causative agent, SARS-CoV-2, has infected millions, globally. The highly contagious nature of this respiratory virus has spurred massive global efforts to develop vaccines at record speeds. In addition to enhanced immunogen delivery, adjuvants may greatly impact protective efficacy of a SARS-CoV-2 vaccine. To investigate adjuvant suitability, we formulated protein subunit vaccines consisting of the recombinant S1 domain of SARS-CoV-2 Spike protein alone or in combination with either CoVaccine HT™ or Alhydrogel. CoVaccine HT™ induced high titres of antigen-binding IgG after a single dose, facilitated affinity maturation and class switching to a greater extent than Alhydrogel and elicited potent cell-mediated immunity as well as virus neutralizing antibody titres. Data presented here suggests that adjuvantation with CoVaccine HT™ can rapidly induce a comprehensive and protective immune response to SARS-CoV-2.

Clinical features and laboratory diagnosis of emerging arthropod-transmitted viruses: A Report from the Pan American Society for Clinical Virology Clinical Practice Committee

Arthropod-borne viruses (arboviruses) are an increasing global threat due to their ability to cause human disease and their expanding geographical distribution. They circulate in nature between arthropod vectors and vertebrate hosts. Infection of susceptible human hosts leads to harmful developmental and neurological manifestations. Arboviruses have caused recent outbreaks with significant public health implications, such as the Zika virus outbreak in the western hemisphere which caused fetal abnormalities in some infected pregnant women, or Eastern Equine Encephalitis which caused 15 deaths in 2019. This review discusses several arboviral infections and their clinical manifestations while highlighting the importance of laboratory diagnostics to detect infections and current attempts at vaccine development. The ability to accurately diagnose an arbovirus infection is critical for initiating a timely response to infections in order to improve patient outcomes.

A recombinant platform for flavivirus vaccines and diagnostics using chimeras of a new insect-specific virus

Flaviviruses such as dengue, yellow fever, Zika, West Nile, and Japanese encephalitis virus present substantial global health burdens. New vaccines are being sought to address safety and manufacturing issues associated with current live attenuated vaccines. Here, we describe a new insect-specific flavivirus, Binjari virus, which was found to be remarkably tolerant for exchange of its structural protein genes (prME) with those of the aforementioned pathogenic vertebrate-infecting flaviviruses (VIFs). Chimeric BinJ/VIF-prME viruses remained replication defective in vertebrate cells but replicated with high efficiency in mosquito cells. Cryo-electron microscopy and monoclonal antibody binding studies illustrated that the chimeric BinJ/VIF-prME virus particles were structurally and immunologically similar to their parental VIFs. Pilot manufacturing in C6/36 cells suggests that high yields can be reached up to 10^9.5 cell culture infectious dose/ml or ≈7 mg/liter. BinJ/VIF-prME viruses showed utility in diagnostic (microsphere immunoassays and ELISAs using panels of human and equine sera) and vaccine applications (illustrating protection against Zika virus challenge in murine IFNAR^-/- mouse models). BinJ/VIF-prME viruses thus represent a versatile, noninfectious (for vertebrate cells), high-yield technology for generating chimeric flavivirus particles with low biocontainment requirements.

CoVaccine HT™ adjuvant potentiates robust immune responses to recombinant SARS-CoV-2 Spike S1 immunisation

The current COVID-19 pandemic has claimed hundreds of thousands of lives and its causative agent, SARS-CoV-2, has infected millions, globally. The highly contagious nature of this respiratory virus has spurred massive global efforts to develop vaccines at record speeds. In addition to enhanced immunogen delivery, adjuvants may greatly impact protective efficacy of a SARS-CoV-2 vaccine. To investigate adjuvant suitability, we formulated protein subunit vaccines consisting of the recombinant S1 domain of SARS-CoV-2 Spike protein alone or in combination with either CoVaccine HT™ or Alhydrogel. CoVaccine HT™ induced high titres of antigen-binding IgG after a single dose, facilitated affinity maturation and class switching to a greater extent than Alhydrogel and elicited potent cell-mediated immunity as well as virus neutralising antibody titres. Data presented here suggests that adjuvantation with CoVaccine HT™ can rapidly induce a comprehensive and protective immune response to SARS-CoV-2.

Comparative specificity and sensitivity of NS1-based serological assays for the detection of flavivirus immune response

Flaviviruses are relevant animal and human pathogens of increasing importance worldwide. The similarities of the initial clinical symptoms and the serological cross-reactivity of viral structural antigens make a laboratory diagnosis of flavivirus infection problematic. The main aim of the present study was the comparative specificity and sensitivity analysis of the non-structural protein NS1 as an antigen to detect flavivirus antibodies in sera from exposed individuals. A strategy for the purification of native recombinant non-structural protein 1 of representative flaviviruses including tick-borne encephalitis, West Nile, Zika and dengue virus was developed. The immunological properties of the purified antigens were analyzed using sera of immunized mice and of infected individuals in comparison with standard commercial assays. Recombinant NS1 protein was confirmed as a valuable option for the detection of flavivirus antibodies with reduced cross-reactivity and high sensitivity offering additional advantages for the detection of vaccine breakthrough cases.

Use of the rSpaA415 antigen indicates low rates of Erysipelothrix rhusiopathiae infection in farmed cattle from the United States of America and Great Britain

Background

Clinical cases of Erysipelothrix rhusiopathiae, a zoonotic gram-positive bacterium, have been reported in many ruminant species, including in cattle, deer, moose and muskoxen. Fatal cases have been repeatedly reported in cattle over the years but to date there is only one Japanese study investigating the seroprevalence of this bacterium in cattle using the growth agglutination test (GAT). This technique is subjective, time-consuming, expensive and hazardous compared to modern serological tests such as enzyme-linked immunosorbent assays (ELISA) or the newly developed fluorescent microbead-based immunoassays (FMIA).

Results

The FMIA based on the surface protein SpaA (rSpaA415) antigen of E. rhusiopathiae developed in this study had an almost perfect agreement with the GAT (k = 0.83) and showed a sensitivity of 89.7% and a specificity of 92.9% when compared to the GAT. Overall, detection rates of E. rhusiopathiae antibody positive samples were 13.8% (51/370) in British herds and 6% (12/200) in US herds. Positive cattle were present in 34.3% (24/70) of the investigated British farms and in 34.7% (8/23) of the US farms with an on-farm prevalence of 7.1 to 100% for the British farms and 8.3–30% for the US farms.

Conclusions

FMIA is a fast, safe and economic alternative to the GAT for the diagnosis of E. rhusiopathiae in cattle. This work is the first seroprevalence study of E. rhusiopathiae in healthy farmed cattle in Great Britain and the US and revealed that infection occurs at a low level. Further investigations to evaluate risks of zoonotic transmission when handling cattle are needed.

Serological evidence of Ebola virus exposure in dogs from affected communities in Liberia: A preliminary report

Filoviruses such as Ebola virus (EBOV) cause outbreaks of viral hemorrhagic fevers for which no FDA-approved vaccines or drugs are available. The 2014-2016 EBOV outbreak in West Africa infected approximately 30,000 people, killing more than 11,000 and affecting thousands more in areas still suffering from the effects of civil wars. Sierra Leone and Liberia reported EBOV cases in every county demonstrating the efficient spread of this highly contagious virus in the well-connected societies of West Africa. In communities, canines are often in contact with people while scavenging for food, which may include sickly bush animals or, as reported from the outbreak, EBOV infected human bodies and excrement. Therefore, dogs may serve as sentinel animals for seroprevalence studies of emerging infectious viruses. Further, due to their proximity to humans, they may have important One Health implications while offering specimens, which may be easier to obtain than human serum samples. Previous reports on detecting EBOV exposure in canines have been limited. Herein we describe a pilot project to detect IgG-responses directed against multiple filovirus and Lassa virus (LASV) antigens in dogs from EBOV affected communities in Liberia. We used a multiplex Luminex-based microsphere immunoassay (MIA) to detect dog IgG binding to recombinant filovirus antigens or LASV glycoprotein (GP) in serum from dogs that were old enough to be present during the EBOV outbreak. We identified 47 (73%) of 64 dog serum samples as potentially exposed to filoviruses and up to 100% of the dogs from some communities were found to have elevated levels of EBOV antigen-binding IgG titers. The multiplex MIA described in this study provides evidence for EBOV IgG antibodies present in dogs potentially exposed to the virus during the 2014-16 outbreak in Liberia. These data support the feasibility of canines as EBOV sentinels and provides evidence that seroprevalence studies in dogs can be conducted using suitable assays even under challenging field conditions. Further studies are warranted to collect data and to define the role canines may play in transmission or detection of emerging infectious diseases.

Use of the immunoglobulin G avidity assay to differentiate between recent Zika and past dengue virus infections

Zika (ZIKV) and dengue (DENV) virus infections elicit a robust but cross-reactive antibody response against the viral envelope protein, while antibody responses against non-structural proteins (NS) are more virus specific. Building on this premise, we have previously developed a flavivirus multiplex microsphere immunoassay (MIA) for the serologic diagnosis of ZIKV and DENV infections. This assay significantly improved diagnostic accuracy; however, MIA could not differentiate more recent from past infections, which still represents a major diagnostic challenge. Therefore, an immunoglobulin G (IgG) based avidity assay was developed and its diagnostic performance evaluated. Specimens from New York State residents were submitted to the Wadsworth Center New York State Department of Health (NYSDOH) for routine clinical testing by Zika IgM ELISA and plaque reduction neutralization test (PRNT). Using our previously developed flavivirus MIA as a platform, we developed an IgG avidity assay to discriminate recent ZIKV from past DENV infections. Zika IgM positive specimens had an average Zika IgG avidity index of 14.8% (95% CI: 11.0-18.4%), while Zika IgM negative but flavivirus MIA and PRNT positive samples had an average Zika IgG avidity index of 34.9% (95% CI: 31.1-38.7%). Specimens positive for dengue antibodies by flavivirus MIA and PRNT had an average dengue IgG avidity index of 68.7% (95% CI: 62.7-75.0%). The IgG avidity assay accurately distinguished recent ZIKV from past DENV infections in patients who traveled to dengue endemic regions. This assay could be very useful in patients with high risk of Zika complications such as pregnant women and monitoring immune responses in vaccine trials.

Clinical Problem-Solving: Fever and Rapidly Progressive Weakness in an Immunocompromised Patient

Here we report the challenging case of a 41-year-old man with HIV complicated by AIDS and a history of prior neurologic injury from progressive multifocal leukoencephalopathy who presented with headache, fevers, lower extremity weakness, hyperreflexic upper extremities, and diminished lower extremity reflexes. We review the clinical decision-making and differential diagnosis for this presentation as the physical examination evolved and diagnostic testing changed over time.

Development of Zika Virus Serological Testing Strategies in New York State

The recent outbreak of Zika virus (ZIKV) in the Americas has challenged diagnostic laboratory testing strategies. At the Wadsworth Center, ZIKV serological testing was performed for over 10,000 specimens, using a combination of an enzyme-linked immunosorbent assay (ELISA) for IgM antibodies (Abs) to ZIKV, a polyvalent microsphere immunoassay (MIA) to detect Abs broadly reactive with flaviviruses, and a plaque reduction neutralization test (PRNT) for further testing. Overall, 42% of patients showed serological evidence of flavivirus infection (primarily past dengue virus [DENV] infection), while 7% possessed IgM Abs to ZIKV and/or DENV. ZIKV IgM Abs typically arose within 3 to 4 days, with only one instance of duration beyond 100 days after reported symptoms. PRNT analysis of 826 IgM-positive specimens showed 7% positive neutralization to ZIKV alone, 9% to DENV alone, and 85% to both ZIKV and DENV. Thus, the extensive Ab cross-reactivity among flaviviruses significantly reduced the value of performing PRNT analysis, especially when a traditional paired serum algorithm with viral neutralization titering was used. Nevertheless, the finding of a negative ZIKV result by PRNT was invaluable for reassuring both physicians and patients. The MIA detected both IgM and IgG, which enabled us to identify patients who presented without IgM anti-ZIKV Abs but still had ZIKV-specific neutralizing Abs. On the basis of these results, a new algorithm, which included an IgM Ab capture (MAC)-ELISA to detect recent infection, a flavivirus MIA to identify patients no longer producing IgM, and a single-dilution PRNT for ZIKV exclusion and occasional discrimination of ZIKV and DENV, was implemented.

Recombinant Zika Virus Subunits Are Immunogenic and Efficacious in Mice

The recent outbreaks of Zika virus (ZIKV) infection in French Polynesia, the Caribbean, and the Americas have highlighted the severe neuropathological sequelae that such an infection may cause. The development of a safe, effective ZIKV vaccine is critical for several reasons: (i) the difficulty in diagnosing an active infection due to common nonspecific symptoms, (ii) the lack of a specific antiviral therapy, and (iii) the potentially devastating pathological effects of in utero infection. Moreover, a vaccine with an excellent safety profile, such as a nonreplicating, noninfectious vaccine, would be ideal for high-risk people (e.g., pregnant women, immunocompromised patients, and elderly individuals). This report describes the development of a recombinant subunit protein vaccine candidate derived from stably transformed insect cells expressing the ZIKV envelope protein in vitro, the primary antigen to which effective virus-neutralizing antibodies are engendered by immunized animals for several other flaviviruses; the vaccine candidate elicits effective virus-neutralizing antibodies against ZIKV and provides protection against ZIKV infection in mice.

Following the 2015 Zika virus (ZIKV) outbreaks in the South Pacific, Caribbean, and Americas, ZIKV has emerged as a serious threat due to its association with infantile microcephaly and other neurologic disorders. Despite an international effort to develop a safe and effective vaccine to combat congenital Zika syndrome and ZIKV infection, only DNA and mRNA vaccines encoding the precursor membrane (prM) and envelope (E) proteins, an inactivated-ZIKV vaccine, and a measles virus-based ZIKV vaccine are currently in phase I or II (prM/E DNA) clinical trials. A ZIKV vaccine based on a nonreplicating, recombinant subunit platform offers a higher safety profile than other ZIKV vaccine candidates but is still highly immunogenic, inducing high virus-neutralizing antibody titers. Here, we describe the production and purification of Drosophila melanogaster S2 insect cell-derived, soluble ZIKV E protein and evaluate its immunogenicity and efficacy in three different mouse strains. As expected, significant virus-specific antibody titers were observed when using formulations containing clinically relevant adjuvants. Immunized mice challenged with live virus demonstrate inhibition of virus replication. Importantly, plaque reduction neutralization tests (PRNTs) indicate the high-titer production of neutralizing antibodies, a correlate of protection in the defense against ZIKV infection. ZIKV challenge of immunocompetent mice led to full protection against viremia with two doses of adjuvanted vaccine candidates. These data demonstrate a proof of concept and establish recombinant subunit immunogens as an effective vaccine candidate against ZIKV infection.

IMPORTANCE The recent outbreaks of Zika virus (ZIKV) infection in French Polynesia, the Caribbean, and the Americas have highlighted the severe neuropathological sequelae that such an infection may cause. The development of a safe, effective ZIKV vaccine is critical for several reasons: (i) the difficulty in diagnosing an active infection due to common nonspecific symptoms, (ii) the lack of a specific antiviral therapy, and (iii) the potentially devastating pathological effects of in utero infection. Moreover, a vaccine with an excellent safety profile, such as a nonreplicating, noninfectious vaccine, would be ideal for high-risk people (e.g., pregnant women, immunocompromised patients, and elderly individuals). This report describes the development of a recombinant subunit protein vaccine candidate derived from stably transformed insect cells expressing the ZIKV envelope protein in vitro, the primary antigen to which effective virus-neutralizing antibodies are engendered by immunized animals for several other flaviviruses; the vaccine candidate elicits effective virus-neutralizing antibodies against ZIKV and provides protection against ZIKV infection in mice.

Utility of Japanese encephalitis virus subgenomic replicon-based single-round infectious particles as antigens in neutralization tests for Zika virus and three other flaviviruses

The introduction of a foreign virus into an area may cause an outbreak, as with the Zika virus (ZIKV) outbreak in the Americas. Preparedness for handling a viral outbreak involves the development of tests for the serodiagnosis of foreign virus infections. We previously established a gene-based technology to generate some flaviviral antigens useful for functional antibody assays. The technology utilizes a Japanese encephalitis virus subgenomic replicon to generate single-round infectious particles (SRIPs) that possess designed surface antigens. In the present study, we successfully expanded the capacity of SRIPs to four human-pathogenic mosquito-borne flaviviruses that could potentially be introduced from endemic to non-endemic countries: ZIKV, Sepik virus, Wesselsbron virus, and Usutu virus. Flavivirus-crossreactive monoclonal antibodies dose-dependently neutralized these SRIPs. ZIKV-SRIPs also produced antibody-dose-dependent neutralization curves equivalent to those shown by authentic ZIKV particles using sera from a Zika fever patient. The faithful expression of designed surface antigens on SRIPs will allow their use in neutralization tests to diagnose foreign flaviviral infections.

Microbeads preparation with reversed-phase microemulsion and ultraviolet light curing for digital encoding suspension array

Microbeads preparation with reversed-phase microemulsion and ultraviolet light curing for digital encoding suspension array.

Digital barcodes of suspension array using laser induced breakdown spectroscopy

We show a coding method of suspension array based on the laser induced breakdown spectroscopy (LIBS), which promotes the barcodes from analog to digital. As the foundation of digital optical barcodes, nanocrystals encoded microspheres are prepared with self-assembly encapsulation method. We confirm that digital multiplexing of LIBS-based coding method becomes feasible since the microsphere can be coded with direct read-out data of wavelengths, and the method can avoid fluorescence signal crosstalk between barcodes and analyte tags, which lead to overall advantages in accuracy and stability to current fluorescent multicolor coding method. This demonstration increases the capability of multiplexed detection and accurate filtrating, expanding more extensive applications of suspension array in life science.

Development and in-use evaluation of a novel Luminex MicroPlex microsphere-based (TRIOL) assay for simultaneous identification of Mycobacterium tuberculosis and detection of first-line and second-line anti-tuberculous drug resistance in China

AIMS

Rapid and accurate diagnostic assays with simultaneous microbial identification and drug resistance detection are essential for optimising treatment and control of tuberculosis.

METHODS

We developed a novel multiplex (TRIOL, Tuberculosis-Rifampicin-Isoniazid-Ofloxacin-Luminex) assay using the Luminex xMAP system that simultaneously identifies Mycobacterium tuberculosis and detects resistance to first-line and second-line anti-tuberculous drugs, and compared its performance with that by PCR sequencing, using phenotypic drug susceptibility testing as the gold standard.

RESULTS

Identification of M. tuberculosis by the TRIOL assay was highly sensitive (100%) and specific (100%). The overall drug-specific specificities were excellent (100%). The overall sensitivity of the TRIOL assay was lower than that of the PCR-sequencing assays (72.4% vs 82.8%) because of a lower sensitivity of detecting rifampicin resistance (71.4% vs 92.9%). The sensitivity of detecting isoniazid and ofloxacin resistance was as good as the PCR-sequencing assays. Importantly, the TRIOL assay did not miss any mutations that were included in the assay. All of the resistant isolates that were missed had uncommon mutations or unknown resistance mechanisms that were not included in the assay.

CONCLUSIONS

The TRIOL assay has higher throughput, lower cost and is less labour intensive than the PCR-sequencing assays. The TRIOL assay is advantageous in having the capability to detect resistance to multiple drugs and an open-architecture system that allows addition of more specific primers to detect uncommon mutations. Inclusion of additional primers for the identification of non-tuberculous mycobacteria, spoligotyping and improvement of rifampicin resistance detection would enhance the use of the TRIOL assay in future clinical and epidemiological studies.

Detection of Antibodies to West Nile Virus in Equine Sera Using Microsphere Immunoassay

One hundred and ninety-one sera from horses that recently were exposed to West Nile virus (WNV) by either vaccination or natural infection or that were not vaccinated and remained free of infection were used to evaluate fluorescent microsphere immunoassays (MIAs) incorporating recombinant WNV envelope protein (rE) and recombinant nonstructural proteins (rNS1, rNS3, and rNS5) for detection of equine antibodies to WNV. The rE MIA had a diagnostic sensitivity and specificity, respectively, of 99.3% and 97.4% for detection of WNV antibodies in the serum of horses that were recently vaccinated or naturally infected with WNV, as compared to the plaque reduction neutralization test (PRNT). The positive rE MIA results were assumed to be WNV-specific because of the close agreement between this assay and the PRNT and the fact that unvaccinated control horses included in this study were confirmed to be free of exposure to the related St Louis encephalitis virus. The NS protein–based MIA were all less sensitive than either the rE MIA or PRNT (sensitivity 0–48.0), although the rNS1 MIA distinguished horses vaccinated with the recombinant WNV vaccine from those that were immunized with the inactivated WNV vaccine ( P < 0.0001) or naturally infected with WNV ( P < 0.0001). The rE MIA would appear to provide a rapid, convenient, inexpensive, and accurate test for the screening of equine sera for the presence of antibodies to WNV.

Microsphere integrated microfluidic disk: synergy of two techniques for rapid and ultrasensitive dengue detection

The application of microfluidic devices in diagnostic systems is well-established in contemporary research. Large specific surface area of microspheres, on the other hand, has secured an important position for their use in bioanalytical assays. Herein, we report a combination of microspheres and microfluidic disk in a unique hybrid platform for highly sensitive and selective detection of dengue virus. Surface engineered polymethacrylate microspheres with carefully designed functional groups facilitate biorecognition in a multitude manner. In order to maximize the utility of the microspheres' specific surface area in biomolecular interaction, the microfluidic disk was equipped with a micromixing system. The mixing mechanism (microballoon mixing) enhances the number of molecular encounters between spheres and target analyte by accessing the entire sample volume more effectively, which subsequently results in signal amplification. Significant reduction of incubation time along with considerable lower detection limits were the prime motivations for the integration of microspheres inside the microfluidic disk. Lengthy incubations of routine analytical assays were reduced from 2 hours to 5 minutes while developed system successfully detected a few units of dengue virus. Obtained results make this hybrid microsphere-microfluidic approach to dengue detection a promising avenue for early detection of this fatal illness.

A High-Performance Multiplex Immunoassay for Serodiagnosis of Flavivirus-Associated Neurological Diseases in Horses

West Nile virus (WNV), Japanese encephalitis virus (JEV), and tick-borne encephalitis virus (TBEV) are flaviviruses responsible for severe neuroinvasive infections in humans and horses. The confirmation of flavivirus infections is mostly based on rapid serological tests such as enzyme-linked immunosorbent assays (ELISAs). These tests suffer from poor specificity, mainly due to antigenic cross-reactivity among flavivirus members. Robust diagnosis therefore needs to be validated through virus neutralisation tests (VNTs) which are time-consuming and require BSL3 facilities. The flavivirus envelope (E) glycoprotein ectodomain is composed of three domains (D) named DI, DII, and DIII, with EDIII containing virus-specific epitopes. In order to improve the serological differentiation of flavivirus infections, the recombinant soluble ectodomain of WNV E (WNV.sE) and EDIIIs (rEDIIIs) of WNV, JEV, and TBEV were synthesised using the Drosophila S2 expression system. Purified antigens were covalently bonded to fluorescent beads. The microspheres coupled to WNV.sE or rEDIIIs were assayed with about 300 equine immune sera from natural and experimental flavivirus infections and 172 nonimmune equine sera as negative controls. rEDIII-coupled microspheres captured specific antibodies against WNV, TBEV, or JEV in positive horse sera. This innovative multiplex immunoassay is a powerful alternative to ELISAs and VNTs for veterinary diagnosis of flavivirus-related diseases.

Immune markers associated with host susceptibility to infection with West Nile virus

Infections with West Nile virus (WNV) are typically asymptomatic, but some patients experience severe neurological disease and even death. Over 1500 fatalities have resulted from the more than 37,000 WNV cases in the USA between 1999 and 2012. While it is clear that age is a significant risk factor, markers of immune status associated with susceptibility to severe infections are incompletely defined. We have taken advantage of stable characteristics of individual status to profile immune markers from a stratified cohort of healthy subjects with a history of asymptomatic or severe infection with WNV. We characterized individual variations in antibody and serum cytokine levels and genome-wide transcriptional profiles of peripheral blood cells (PBMCs). While antibody levels were not significantly different between cohorts, we found that subjects with a history of severe infection had significantly lower levels of serum IL-4, and that these changes in IL-4 levels were associated with altered gene expression patterns in PBMCs. In addition, we identified a signature of 105 genes that displayed altered expression levels when comparing subjects with a history of asymptomatic or severe infection. These results suggest that systems-level analysis of immune system status can be used to identify factors relevant for susceptibility to severe infections, and specifically point to an important contribution for IL-4 in resistance to WNV infection.

George K, Chatterjee D, Prusinski M, Wormser GP, Wong SJ. Potential role of deer tick virus in Powassan encephalitis cases in Lyme disease-endemic areas of New York, U.S.A

TOC Summary: The epidemiologic pattern and limited laboratory testing indicate that this virus lineage might account for most of these illnesses.

Powassan virus, a member of the tick-borne encephalitis group of flaviviruses, encompasses 2 lineages with separate enzootic cycles. The prototype lineage of Powassan virus (POWV) is principally maintained between Ixodes cookei ticks and the groundhog (Marmota momax) or striped skunk (Mephitis mephitis), whereas the deer tick virus (DTV) lineage is believed to be maintained between Ixodes scapularis ticks and the white-footed mouse (Peromyscus leucopus). We report 14 cases of Powassan encephalitis from New York during 2004–2012. Ten (72%) of the patients were residents of the Lower Hudson Valley, a Lyme disease–endemic area in which I. scapularis ticks account for most human tick bites. This finding suggests that many of these cases were caused by DTV rather than POWV. In 2 patients, DTV infection was confirmed by genetic sequencing. As molecular testing becomes increasingly available, more cases of Powassan encephalitis may be determined to be attributable to the DTV lineage.

Development of an algorithm for production of inactivated arbovirus antigens in cell culture

Arboviruses are medically important pathogens that cause human disease ranging from a mild fever to encephalitis. Laboratory diagnosis is essential to differentiate arbovirus infections 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 virus-specific immunoglobulin M antibody-capture enzyme-linked immunosorbent assay (MAC-ELISA). Antigen production in cell culture has largely replaced the use of suckling mice; however, the methods are not directly transferable. The development of a cell culture antigen production algorithm for nine arboviruses from the three main arbovirus families, Flaviviridae, Togaviridae, and Bunyaviridae, is described here. Virus cell culture growth and harvest conditions were optimized, inactivation methods were evaluated, and concentration procedures were compared for each virus. Antigen performance was evaluated by the MAC-ELISA at each step of the procedure. The antigen production algorithm is a framework for standardization of methodology and quality control; however, a single antigen production protocol was not applicable to all arboviruses and needed to be optimized for each virus.

Systematic reference sample generation for multiplexed serological assays

Quality controls of serological assays have to contain defined amounts of human antibodies specific for the targeted antigen. A prevailing issue for array-based antigen assays is that dozens of antigens are targeted within the same assay. Commonly different patient sera are combined and optimal pools are empirically identified. Here, we report a mathematical approach how an optimal sample pool composition can be systematically calculated and accurately compiled. The approach was used to compose suitable quality controls for a 71 plex Tuberculosis antigen bead array using a limited number of positive human sera.

Predicted and observed mortality from vector-borne disease in small songbirds

Numerous diseases of wildlife have recently emerged due to trade and travel. However, the impact of disease on wild animal populations has been notoriously difficult to detect and demonstrate, due to problems of attribution and the rapid disappearance of bodies after death. Determining the magnitude of avian mortality from West Nile virus (WNV) is emblematic of these challenges. Although correlational analyses may show population declines coincident with the arrival of the virus, strong inference of WNV as a cause of mortality or a population decline requires additional evidence. We show how integrating field data on mosquito feeding patterns, avian abundance, and seroprevalence can be used to predict relative mortality from vector-borne pathogens. We illustrate the method with a case study on WNV in three species of small songbirds, tufted titmouse (Baeolophus bicolor), Carolina wrens (Thryothorus ludovicianus), and northern cardinals (Cardinalis cardinalis). We then determined mortality, infectiousness, and behavioral response of wrens and titmouse following infection with WNV in laboratory experiments and compared them to a previous study on WNV mortality in cardinals. In agreement with predictions, we found titmouse had the highest mortality from WNV infection, with 100% of eleven birds perishing within seven days after infection. Mortality in wrens was significantly lower at 27% (3/11), but still substantial. Viremia profiles indicated that both species were highly infectious for WNV and could play roles in WNV amplification. These findings suggest that WNV may be killing many small-bodied birds, despite the absence of large numbers of dead birds testing positive for WNV. More broadly, they illustrate a framework for predicting relative mortality in hosts from vector-borne disease.

Domestic cat microsphere immunoassays: detection of antibodies during feline immunodeficiency virus infection

Microsphere immunoassays (MIAs) allow rapid and accurate evaluation of multiple analytes simultaneously within a biological sample. Here we describe the development and validation of domestic cat-specific MIAs for a) the quantification of total IgG and IgA levels in plasma, and b) the detection of IgG and IgA antibodies to feline immunodeficiency virus (FIV) capsid (CA) and surface (SU) proteins, and feline CD134 in plasma. These assays were used to examine the temporal antibody response of domestic cats infected with apathogenic and pathogenic FIVs, and domestic cats infected with parental and chimeric FIVs of varying pathogenicity. The results from these studies demonstrated that a) total IgG antibodies increase over time after infection; b) α-CA and α-SU IgG antibodies are detectable between 9 and 28 days post-infection and increase over time, and these antibodies combined represent a fraction (1.8 to 21.8%) of the total IgG increase due to infection; c) measurable α-CD134 IgG antibody levels vary among individuals and over time, and are not strongly correlated with viral load; d) circulating IgA antibodies, in general, do not increase during the early stage of infection; and e) total IgG, and α-CA and α-SU IgG antibody kinetics and levels vary with FIV viral strain/pathogenicity. The MIAs described here could be used to screen domestic cats for FIV infection, and to evaluate the FIV-specific or total antibody response elicited by various FIV strains/other diseases.

A hamster-derived West Nile virus isolate induces persistent renal infection in mice

Background

West Nile virus (WNV) can persist long term in the brain and kidney tissues of humans, non-human primates, and hamsters. In this study, mice were infected with WNV strain H8912, previously cultured from the urine of a persistently infected hamster, to determine its pathogenesis in a murine host.

Methodology/Principal Findings

We found that WNV H8912 was highly attenuated for neuroinvasiveness in mice. Following a systemic infection, viral RNA could be detected quickly in blood and spleen and much later in kidneys. WNV H8912 induced constitutive IL-10 production, upregulation of IFN-β and IL-1β expression, and a specific IgM response on day 10 post-infection. WNV H8912 persisted preferentially in kidneys with mild renal inflammation, and less frequently in spleen for up to 2.5 months post infection. This was concurrent with detectable serum WNV-specific IgM and IgG production. There were also significantly fewer WNV- specific T cells and lower inflammatory responses in kidneys than in spleen. Previous studies have shown that systemic wild-type WNV NY99 infection induced virus persistence preferentially in spleen than in mouse kidneys. Here, we noted that splenocytes of WNV H8912-infected mice produced significantly less IL-10 than those of WNV NY99-infected mice. Finally, WNV H8912 was also attenuated in neurovirulence. Following intracranial inoculation, WNV persisted in the brain at a low frequency, concurrent with neither inflammatory responses nor neuronal damage in the brain.

Conclusions

WNV H8912 is highly attenuated in both neuroinvasiveness and neurovirulence in mice. It induces a low and delayed anti-viral response in mice and preferentially persists in the kidneys.

West Nile virus (WNV) has been reported to persist long term in the brain and kidney tissues of humans, non-human primates, and hamsters. To define a murine model of persistent WNV renal infection, we characterized infection by WNV H8912, an isolate cultured previously from the urine of a persistently infected hamster. Our findings indicate that WNV strain H8912 is highly attenuated in both neuroinvasiveness and neurovirulence for mice. The virus persisted preferentially in kidneys of the mouse, and less frequently in the spleen and the brain. Moreover, mice infected with WNV H8912 had a delayed induction of IFN- β and IL-1β expression and WNV- specific IgM response, but a constitutive production of serum IL-10. There was a lower proinflammatory response in mouse kidneys when compared to equivalent findings in the spleen. This response may lead to a reduced T cell response in kidneys, which could ultimately contribute to renal-specific WNV persistence. Defining a murine model of WNV persistence by using a well-characterized, hamster-derived WNV urine isolate should provide important insights into understanding the mechanisms of WNV persistence.

Personal genomes, quantitative dynamic omics and personalized medicine

The rapid technological developments following the Human Genome Project have made possible the availability of personalized genomes. As the focus now shifts from characterizing genomes to making personalized disease associations, in combination with the availability of other omics technologies, the next big push will be not only to obtain a personalized genome, but to quantitatively follow other omics. This will include transcriptomes, proteomes, metabolomes, antibodyomes, and new emerging technologies, enabling the profiling of thousands of molecular components in individuals. Furthermore, omics profiling performed longitudinally can probe the temporal patterns associated with both molecular changes and associated physiological health and disease states. Such data necessitates the development of computational methodology to not only handle and descriptively assess such data, but also construct quantitative biological models. Here we describe the availability of personal genomes and developing omics technologies that can be brought together for personalized implementations and how these novel integrated approaches may effectively provide a precise personalized medicine that focuses on not only characterization and treatment but ultimately the prevention of disease.

Diagnosis of acute deer tick virus encephalitis

BACKGROUND

Deer tick virus (DTV) is a tick-borne flavivirus that has only recently been appreciated as a cause of viral encephalitis. We describe the clinical presentation of a patient who had DTV encephalitis diagnosed before death and survived for 8 months despite severe neurologic dysfunction.

METHODS

Diagnosis was made from a cerebrospinal fluid specimen, using a flavivirus-specific polymerase chain-reaction assay followed by sequence confirmation, and the phylogeny was analyzed. Serologic testing, including plaque reduction neutralization testing, was also performed.

RESULTS

Molecular analysis indicated that the virus was closely related to 2 strains of DTV that had been detected in Ixodes scapularis ticks from Massachusetts in 1996 and in the brain of a patient from New York in 2007.

CONCLUSIONS

DTV encephalitis should be considered in the differential diagnosis of encephalitis in geographic areas that are endemic for Lyme disease.

Effect of serum heat-inactivation and dilution on detection of anti-WNV antibodies in mice by West Nile virus E-protein microsphere immunoassay

Immunopathogenesis studies employing West Nile virus (WNV) mice model are important for the development of antivirals and vaccines against WNV. Since antibodies produced in mice early during WNV infection are essential for clearing virus from the periphery, it is important to detect early and persistent anti-WNV antibodies. ELISA and plaque reduction neutralization tests are traditionally used for detection of anti-WNV antibodies and WNV-neutralizing antibodies, respectively. Although these assays are sensitive and specific, they are expensive and time consuming. Microsphere immunoassays (MIA) are sensitive, specific, allow for high throughput, are cost effective, require less time to perform than other methods, and require low serum volumes. Several assay parameters such as serum heat-inactivation (HI) and dilution can alter WNV MIA sensitivity. We examined the effect of these parameters on WNV E-protein MIA (WNV E-MIA) for the enhanced detection of anti-WNV IgM and IgG antibodies. WNV E-MIA was conducted using serial dilutions of HI and non-HI (NHI) serum collected at various time points from mice inoculated with WNV. HI significantly enhanced detection of IgM and IgG antibodies as compared to NHI serum. WNV IgM and IgG antibodies in HI sera were detected earlier at day 3 and IgM antibodies persisted up to day 24 after infection. HI serum at 1∶20 dilution was found to be optimal for detection of both IgM and IgG antibodies as compared to higher-serum dilutions. Further, addition of exogenous complement to the HI serum decreased the WNV E-MIA sensitivity. These results suggest that serum-HI and optimal dilution enhance WNV E-MIA sensitivity by eliminating the complement interference, thereby detecting low-titer anti-WNV antibodies during early and late phases of infection. This improved MIA can also be readily employed for detection of low-titer antibodies for detection of other infectious agents and host proteins.

Validation processes of protein biomarkers in serum--a cross platform comparison

Due to insufficient biomarker validation and poor performances in diagnostic assays, the candidate biomarker verification process has to be improved. Multi-analyte immunoassays are the tool of choice for the identification and detailed validation of protein biomarkers in serum. The process of identification and validation of serum biomarkers, as well as their implementation in diagnostic routine requires an application of independent immunoassay platforms with the possibility of high-throughput. This review will focus on three main multi-analyte immunoassay platforms: planar microarrays, multiplex bead systems and, array-based surface plasmon resonance (SPR) chips. Recent developments of each platform will be discussed for application in clinical proteomics, principles, detection methods, and performance strength. The requirements for specific surface functionalization of assay platforms are continuously increasing. The reasons for this increase is the demand for highly sensitive assays, as well as the reduction of non-specific adsorption from complex samples, and with it high signal-to-noise-ratios. To achieve this, different support materials were adapted to the immobilized biomarker/ligand, allowing a high binding capacity and immobilization efficiency. In the case of immunoassays, the immobilized ligands are proteins, antibodies or peptides, which exhibit a diversity of chemical properties (acidic/alkaline; hydrophobic/hydrophilic; secondary or tertiary structure/linear). Consequently it is more challenging to develop immobilization strategies necessary to ensure a homogenous covered surface and reliable assay in comparison to DNA immobilization. New developments concerning material support for each platform are discussed especially with regard to increase the immobilization efficiency and reducing the non-specific adsorption from complex samples like serum and cell lysates.

Approaches for the development of rapid serological assays for surveillance and diagnosis of infections caused by zoonotic flaviviruses of the Japanese encephalitis virus serocomplex

Flaviviruses are responsible for a number of important mosquito-borne diseases of man and animals globally. The short vireamic period in infected hosts means that serological assays are often the diagnostic method of choice. This paper will focus on the traditional methods to diagnose flaviviral infections as well as describing the modern rapid platforms and approaches for diagnostic antigen preparation.

Multiplex bead assay for serum samples from children in Haiti enrolled in a drug study for the treatment of lymphatic filariasis

A multiplex bead assay (MBA) was used to analyze serum samples collected longitudinally from children enrolled in a drug trial for treatment of filariasis in Leogane, Haiti. Recombinant antigens Bm14 and Bm33 from Brugia malayi, third polar tube protein (PTP3) from Encephalitozoon cuniculi, and merozoite surface protein-1(19) (MSP-1(19)) from Plasmodium falciparum were coupled to carboxylated polystyrene microspheres. IgG responses to PTP3 and MSP-1(19) were not affected by albendazole (ALB), diethylcarbamazine (DEC), or combination of diethylcarbamazine and albendazole (DEC/ALB). However, IgG and IgG4 responses to Bm14 and Bm33 were significantly decreased (P < 0.001) by DEC and DEC/ALB treatment. Antibody responses to Bm14 and Bm33 decreased after DEC treatment (but not placebo) among children who were negative for microfilaremia and antigenemia at baseline, suggesting that these children harbored early stages of infection. The MBA is an excellent serologic technique for multiple antigens that offers substantial advantages over single-antigen based enzyme-linked immunosorbent assay in mass drug administration studies for monitoring changes in antibody levels.

Immune responses to an attenuated West Nile virus NS4B-P38G mutant strain

The nonstructural (NS) proteins of West Nile virus (WNV) have been associated with participation in evasion of host innate immune defenses. In the present study, we characterized immune response to an attenuated WNV strain, which has a P38G substitution in the NS4B protein. The WNV NS4B-P38G mutant induced a lower level of viremia and no lethality in C57BL/6 (B6) mice following a systemic infection. Interestingly, there were higher type 1 IFNs and IL-1β responses compared to mice infected by wild-type WNV. NS4B-P38G mutant-infected mice also showed stronger effector and memory T cell responses. WNV specific antibody responses were not different between mice infected with these two viruses. As a consequence, all mice were protected from a secondary infection with a lethal dose of wild-type WNV following a primary infection with NS4B-P38G mutant. Moreover, NS4B-P38G mutant infection in cultured bone-marrow derived dendritic cells (DCs) were shown to have a reduced replication rate, but a higher level of innate cytokine production than wild-type WNV, some of which were dependent on Myd88 signaling. In conclusion, the NS4B-P38G mutant strain induces higher protective innate and adaptive immune response in mice, which results in a lower viremia and no lethality in either primary or secondary infection, suggesting a high potential as an attenuating mutation in a vaccine candidate.

Simultaneous detection of antibodies to mouse hepatitis virus recombinant structural proteins by a microsphere-based multiplex fluorescence immunoassay

We describe a new microsphere-based multiplex fluorescent immunoassay (MFI) using recombinant mouse hepatitis virus (MHV) proteins to detect antibodies to coronaviruses in mouse and rat sera. All the recombinant proteins, including nucleocapsid (N) and 3 subunits of spike protein, S1, S2, and Smid, showed positive reactivity in MFI with mouse antisera to 4 MHV strains (MHV-S, -A59, -JHM, and -Nu67) and rat antiserum to a strain of sialodacryoadenitis virus (SDAV-681). The MFI was evaluated for its diagnostic power, with panels of mouse sera classified as positive or negative for anti-MHV antibodies by enzyme-linked immunosorbent assay (ELISA) using MHV virion antigen and indirect fluorescent antibody assay. The reactivities of 236 naturally infected mouse sera were examined; 227 samples were positive by MFI using S2 antigen (96% sensitivity), and 208 samples were positive using N antigen (88% sensitivity). Based on the assessment by MFI using the S2 and N antigens, only 3 serum samples showed double-negative results, indicating a false-negative rate of 1.3%. In 126 uninfected mouse sera, including 34 ELISA false-positive sera, only 7 samples showed false-positive results by MFI using either the S2 or N antigen (94% specificity). Similarly, the S2 and N antigen-based MFI was 98% sensitive and 100% specific in detecting anticoronavirus antibodies in rat sera. Thus, this MFI-based serologic assay using the S2 and N antigens promises to be a reliable diagnostic method, representing a highly sensitive and specific alternative to traditional ELISA for detection of coronavirus infections in laboratory mouse and rat colonies.

Persistence of virus-specific immune responses in the central nervous system of mice after West Nile virus infection

BACKGROUND

West Nile virus (WNV) persists in humans and several animal models. We previously demonstrated that WNV persists in the central nervous system (CNS) of mice for up to 6 months post-inoculation. We hypothesized that the CNS immune response is ineffective in clearing the virus.

RESULTS

Immunocompetent, adult mice were inoculated subcutaneously with WNV, and the CNS immune response was examined at 1, 2, 4, 8, 12 and 16 weeks post-inoculation (wpi). Characterization of lymphocyte phenotypes in the CNS revealed elevation of CD19+ B cells for 4 wpi, CD138 plasma cells at 12 wpi, and CD4+ and CD8+ T cells for at least 12 wpi. T cells recruited to the brain were activated, and regulatory T cells (Tregs) were present for at least 12 wpi. WNV-specific antibody secreting cells were detected in the brain from 2 to 16 wpi, and virus-specific CD8+ T cells directed against an immunodominant WNV epitope were detected in the brain from 1 to 16 wpi. Furthermore, these WNV-specific immune responses occurred in mice with and without acute clinical disease.

CONCLUSIONS

Virus-specific immune cells persist in the CNS of mice after WNV infection for up to 16 wpi.

Detection of West Nile virus

West Nile virus (WNV; Flavivirus, Flaviviridae) is a spherical enveloped virion containing single-stranded, positive-sense RNA, approximately 11 kb in length. The virus is the most widely distributed flavivirus in the world. Genetic analysis reveals two major lineages of virus, I and II, and several possible newly recognized lineages. Lineage I strains are most commonly associated with outbreaks of neurologic disease, although lineage II virus has led to large epidemics of fever, as in South Africa in 1974. Infection with WNV leads to a wide range of diseases from mildly febrile to severely neurologic, but asymptomatic -infections occur most frequently. Approximately one in 140 infected individuals develop neurologic -disease. The virus is maintained in an enzootic cycle, where it is transmitted between ornithophilic mosquitoes of the Culex genus and predominantly passeriform birds. Equines and humans are considered incidental hosts since they do not mount high enough viremia for mosquitoes to become infected -following feeding. Laboratory diagnosis of WNV infection is predominantly serological, although -caution is advised because of the high degree of cross-reactivity among flaviviruses. Field specimens, especially mosquitoes and dead birds, collected as part of surveillance programs, are tested for the presence of viral nucleic acid, viral antigen, or infectious virus. Rapid test protocols have been developed in response to the expansion of WNV in the United States. Since WNV is classified as a Biosafety Level-3 (BSL-3) agent by CDC, it is recommended that once this virus is identified in a diagnostic specimen, all infectious virus should be handled in a BSL-3 laboratory in Class II biosafety cabinets by laboratory staff who are trained to work at this level of containment. Assay protocols are described and the necessary equipment and supplies listed.

Persistence of West Nile virus in the central nervous system and periphery of mice

Most acute infections with RNA viruses are transient and subsequently cleared from the host. Recent evidence, however, suggests that the RNA virus, West Nile virus (WNV), not only causes acute disease, but can persist long term in humans and animal models. Our goal in this study was to develop a mouse model of WNV persistence. We inoculated immunocompetent mice subcutaneously (s.c.) with WNV and examined their tissues for infectious virus and WNV RNA for 16 months (mo) post-inoculation (p.i.). Infectious WNV persisted for 1 mo p.i. in all mice and for 4 mo p.i. in 12% of mice, and WNV RNA persisted for up to 6 mo p.i. in 12% of mice. The frequency of persistence was tissue dependent and was in the following order: skin, spinal cord, brain, lymphoid tissues, kidney, and heart. Viral persistence occurred in the face of a robust antibody response and in the presence of inflammation in the brain. Furthermore, persistence in the central nervous system (CNS) and encephalitis were observed even in mice with subclinical infections. Mice were treated at 1 mo p.i. with cyclophosphamide, and active viral replication resulted, suggesting that lymphocytes are functional during viral persistence. In summary, WNV persisted in the CNS and periphery of mice for up to 6 mo p.i. in mice with subclinical infections. These results have implications for WNV-infected humans. In particular, immunosuppressed patients, organ transplantation, and long term sequelae may be impacted by WNV persistence.

Simultaneous detection of five biothreat agents in powder samples by a multiplexed suspension array

A suspension array-based multiplexed immunoassay was developed for rapid, sensitive, specific, and simultaneous detection of multiple biothreat-associated agents in powder samples. The 5-plexed immunoassays using sets of 9-plexed coupled fluorescent beads were employed to simultaneously detect five representative biothreat agents, including B. anthracis spore, Y. pestis, SARS-CoV, staphylococcal enterotoxin B (SEB) and ricin from a single powder sample and the feasibility for field samples was demonstrated by both blinded and standard laboratory trials. The detection sensitivity and dynamic range for the five biothreat agents from different powders might be varied depending on the nature of the powder and the feature of the contaminating agent. The limit of detection for Y. pestis, B. anthracis spores, SEB, ricin, SARS-CoV N protein in milk powder was 20 cfu, 111 cfu, 110pg, 5.4 ng and 2 ng per test respectively. Compared to conventional ELISA method, the suspension array has a higher sensitive ability, and can detect five biothreat agents simultaneously with high reproducibility.

Progress on the development of therapeutics against West Nile virus

A decade has passed since the appearance of West Nile virus (WNV) in humans in the Western Hemisphere in New York City. During this interval, WNV spread inexorably throughout North and South America and caused millions of infections ranging from a sub-clinical illness, to a self-limiting febrile syndrome or lethal neuroinvasive disease. Its entry into the United States triggered intensive research into the basic biology of WNV and the elements that comprise a protective host immune response. Although no therapy is currently approved for use in humans, several strategies are being pursued to develop effective prophylaxis and treatments. This review describes the current state of knowledge on epidemiology, clinical presentation, pathogenesis, and immunobiology of WNV infection, and highlights progress toward an effective therapy.