Detection of IgG and IgM to West Nile Virus

Metal organic framework encapsulated tamavidin-Gluc reporter: application in COVID-19 spike antigen bioluminescent immunoassay

Enzyme linked immunosorbent assay (ELISA) is one of the most utilized serological methods to diagnose and identify etiologic agents of many infectious diseases and other physiologically important analytes. ELISA can be used either alone or adjunct to other diagnostic methods such as molecular arrays, and other serological techniques. Most ELISA assays utilize reagents that are proteinaceous in nature, which are not very stable and require cold-chain transport systems. Development of a desirable immunoassay requires stability of reagents used and its ability to be stored at room temperature without sacrificing the activity of the reagents or the protein of interest. Metal organic frameworks (MOFs) are a rapidly emerging and evolving class of porous polymeric materials used in a variety of biosensor applications. In this study, we introduce the use of MOFs to stabilize a universal reporter fusion protein, specifically, avidin-like protein (Tam-avidin2) and the small bioluminescent protein Gaussia luciferase (Gluc) forming the fusion reporter, tamavidin2-Gluc (TA2-Gluc). This fusion protein serves as a universal reporter for any assays that utilize biotin-avidin binding strategy. Using SARS-CoV2 S1 spike antigen as the model target antigen, we demonstrated that encapsulation of TA2-Gluc fusion protein using a nano-porous material, zeolitic imidazolate framework-8 (ZIF-8), allows us to store and preserve this reporter protein at room temperature for over 6 months and use it as a reporter for an ELISA assay. Our optimized assay was validated demonstrating a 0.26 μg mL-1 limit of detection, high reproducibility of assay over days, detection of spiked non-virulent SARS-COV2 pseudovirus in real sample matrix, and detection in real COVID-19 infected individuals. This result can lead to the utilization of our TA2-Gluc fusion protein reporter with other assays and potentially in diagnostic technologies in a point-of-care setting.

Recent progresses and remaining challenges for the detection of Zika virus

Zika virus (ZIKV) has emerged as a particularly notorious mosquito-borne flavivirus, which can lead to a devastating congenital syndrome in the fetuses of pregnant mothers (e.g., microcephaly, spasticity, craniofacial disproportion, miscarriage, and ocular abnormalities) and cause the autoimmune disorder Guillain-Barre' syndrome of adults. Due to its severity and rapid dispersal over several continents, ZIKV has been acknowledged to be a global health concern by the World Health Organization. Unfortunately, the ZIKV has recently resurged in India with the potential for devastating effects. Researchers from all around the world have worked tirelessly to develop effective detection strategies and vaccines for the prevention and control of ZIKV infection. In this review, we comprehensively summarize the most recent research into ZIKV, including the structural biology and evolution, historical overview, pathogenesis, symptoms, and transmission. We then focus on the detection strategies for ZIKV, including viral isolation, serological assays, molecular assays, sensing methods, reverse transcription loop mediated isothermal amplification, transcription-mediated amplification technology, reverse transcription strand invasion based amplification, bioplasmonic paper-based device, and reverse transcription isothermal recombinase polymerase amplification. To conclude, we examine the limitations of currently available strategies for the detection of ZIKV, and outline future opportunities and research challenges.

A Cell-Based Capture Assay for Rapid Virus Detection

Routine methods for virus detection in clinical specimens rely on a variety of sensitive methods, such as genetic, cell culture and immuno-based assays. It is imperative that the detection assays would be reliable, reproducible, sensitive and rapid. Isolation of viruses from clinical samples is crucial for deeper virus identification and analysis. Here we introduce a rapid cell-based assay for isolation and detection of viruses. As a proof of concept several model viruses including West Nile Virus (WNV), Modified Vaccinia Ankara (MVA) and Adenovirus were chosen. Suspended Vero cells were employed to capture the viruses following specific antibody labeling which enables their detection by flow cytometry and immuno-fluorescence microscopy assays. Using flow cytometry, a dose response analysis was performed in which 3.6e4 pfu/mL and 1e6 pfu/mL of MVA and WNV could be detected within two hours, respectively. When spiked to commercial pooled human serum, detection sensitivity was slightly reduced to 3e6 pfu/mL for WNV, but remained essentially the same for MVA. In conclusion, the study demonstrates a robust and rapid methodology for virus detection using flow cytometry and fluorescence microscopy. We propose that this proof of concept may prove useful in identifying future pathogens.

West Nile virus neuroinvasive disease associated with rituximab therapy

West Nile virus neuroinvasive disease (WNVND) manifests with meningitis, encephalitis, and/or acute flaccid paralysis. It represents less than 1% of the clinical syndromes associated with West Nile virus (WNV) infection in immunocompetent patients. Immunosuppressive therapy is associated with increased risk of WNVND and worse prognosis. We present a patient with WNVND during therapy with rituximab, and a review of the literature for previous similar cases with the goal to describe the clinical spectrum of WNVND in patients treated specifically with rituximab. Our review indicates that the most common initial complaints are fever and altered mental status, brain magnetic resonance imaging often shows bilateral thalamic hyperintensities, and cerebrospinal analysis consistently reveals mild lymphocytic pleocytosis with elevated protein, positive WNV polymerase chain reaction, and negative WNV antibodies. Treatment is usually supportive care, with intravenous immunoglobulins (IVIG) plus corticosteroids and WNV-specific IVIG also used. The disease is usually fatal despite intervention. Our patient's presentation was very similar to prior reports, however demonstrated spontaneous improvement with supportive management only. WNVND is a rare and serious infection with poor prognosis when associated with rituximab therapy. Diagnosis is complicated by absent or delayed development of antibodies. The presence of bilateral thalamic involvement is a diagnostic clue for WNVND. There is insufficient evidence to recommend the use of corticosteroids or IVIG.

Macropinocytosis dependent entry of Chikungunya virus into human muscle cells

Chikungunya virus (CHIKV) is a re-emerging arbovirus known to cause chronic myalgia and arthralgia with high morbidity. CHIKV is now considered endemic in many countries across Asia and Africa. In this study, the susceptibility of various human, mammalian and mosquito cell lines to CHIKV infection was evaluated. CHIKV infection was found to be cell-type dependent and virus strain-specific. Furthermore, SJCRH30 (human rhabdomyosarcoma cell line) was showed to be highly permissive to CHIKV infection, with maximum production of infectious virions observed at 12 h.p.i. Pre-infection treatment of SJCRH30 with various inhibitors of endocytosis, including monodansylcadaverine (receptor-mediated endocytic inhibitor), dynasore (clathrin-mediated endocytic inhibitor), as well as filipin (caveolin-mediated endocytosis inhibitor), resulted in minimal inhibition of CHIKV infection. In contrast, dose-dependent inhibition of CHIKV infection was observed with the treatment of macropinocytosis inhibitor, 5-(N-ethyl-N-isopropyl)amiloride (EIPA). Furthermore, siRNA-mediated knockdown of sortin nexin 9 (SNX9) a protein involved in macropinosome formation, also resulted in a significant dose-dependent reduction in viral titre. By performing a virus entry assay, CHIKV particles were also observed to colocalize with FITC-dextran, a macropinosome marker. This study shows for the first time, that the infectious entry of CHIKV into human muscle cells is mediated by macropinocytosis. Together, the data from this study may pave the way for the development of specific inhibitors that target the entry process of CHIKV into cells.

This study revealed the differences in susceptibility of various human, mammalian and mosquito cell lines to CHIKV infection. CHIKV infection was found to be cell-type dependent and virus-strain specific. Additionally, two human muscle cell lines, SJCRH30 (rhabdomyosarcoma cell line) and HSMM (human skeletal muscle myoblasts), were shown to be highly susceptible to infection by different CHIKV strains. Pre-infection treatment of SJCRH30 and HSMM with a macropinocytosis inhibitor, 5-(N-ethyl-N-isopropyl)amiloride (EIPA) showed a dose-dependent inhibition. Additionally, knockdown of a protein involved in macropinocytosis formation, SNX9, revealed that CHIKV infection of SJCRH30 cells relies on macropinocytosis. Results were confirmed with a FITC-dextran assay, which showed colocalisation between CHIKV particles and macropinosomes during viral entry. Overall, this study may contribute to the development of therapeutic interventions using specific inhibitors that target the entry of CHIKV into muscle cells.

Long-term surveillance defines spatial and temporal patterns implicating Culex tarsalis as the primary vector of West Nile virus

West Nile virus (WNV) has become the most epidemiologically important mosquito-borne disease in the United States, causing ~50,000 cases since its introduction in 1999. Transmitted primarily by Culex species, WNV transmission requires the complex interplay between bird reservoirs and mosquito vectors, with human cases the result of epizootic spillover. To better understand the intrinsic factors that drive these interactions, we have compiled infection data from sentinel chickens, mosquito vectors, and human cases in Iowa over a 15 year period (2002-2016) to better understand the spatial and temporal components that drive WNV transmission. Supplementing these findings with mosquito abundance, distribution, and host preferences data, we provide strong support that Culex tarsalis is the most important vector of human WNV infections in the region. Together, our analysis provides new insights into WNV infection patterns in multiple hosts and highlights the importance of long-term surveillance to understand the dynamics of mosquito-borne-disease transmission.

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.

Recent advances in nanoparticle-based lateral flow immunoassay as a point-of-care diagnostic tool for infectious agents and diseases

Recent advances in lateral flow immunoassay-based devices as a point-of-care analytical tool for the detection of infectious diseases are reviewed.

Considerations for screening live kidney donors for endemic infections: a viewpoint on the UNOS policy

In February 2013, the Organ Procurement and Transplantation Network mandated that transplant centers perform screening of living kidney donors prior to transplantation for Strongyloides, Trypanosoma cruzi and West Nile virus (WNV) infection if the donor is from an endemic area. However, specific guidelines for screening were not provided, such as the optimal testing modalities, timing of screening prior to donation and the appropriate selection of donors. In this regard, the American Society of Transplantation Infectious Diseases Community of Practice, together with disease-specific experts, has developed this viewpoint document to provide guidance for the testing of live donors for Strongyloides, T. cruzi and WNV infection, specifically identifying at-risk populations and testing algorithms, including advantages, limitations and interpretation of results.

Laboratory diagnosis of viral infection

Since the last Handbook of Clinical Neurology volume on this topic, viral diagnosis has made tremendous strides, moving from the margin to the mainstream of clinical care. For many years, conventional virus isolation was the mainstay of viral diagnosis since it was sensitive and “open-minded.” However, growth in conventional cell culture entails an inherent delay that limits its clinical impact. Although rapid culture and viral antigen methods detect fewer pathogens and are less sensitive than conventional culture, both require less expertise and have greatly reduced time to result. Polymerase chain reaction has ushered in a new era in virology, especially in the diagnosis of neurologic diseases. Molecular amplification methods are rapid, highly sensitive, can be automated, quantitative, and detect viruses not amenable to routine culture. User-friendly, walk-away tests with results in an hour, as well as multiplex tests that can detect 20 viruses in a single reaction, are now a reality. As the variety of test methods and commercial products proliferate, the challenges for clinicians and laboratories are selecting which tests to utilize in which clinical scenarios, and understanding how to interpret the results. The advantages and limitations of each method are discussed in this chapter, with special attention to neurologic disease.

Diagnostic potential and antigenic properties of recombinant tick-borne encephalitis virus subviral particles expressed in mammalian cells from Semliki Forest virus replicons

The precursor membrane envelope (prME) proteins of all three tick-borne encephalitis virus (TBEV) subtypes were produced based on expression from Semliki Forest virus (SFV) replicons transcribed from recombinant plasmids. Vero E6 cells transfected by these plasmids showed specific reactivities in immunofluorescence and immunoblot assays by monoclonal antibodies against European and Far-Eastern subtype strains of TBEV, indicating proper folding of the expressed glycoproteins. The prME glycoproteins were secreted into the cell culture supernatant, forming TBEV subviral particles of 20 to 30 nm in diameter. IgM μ-capture and IgG monoclonal antibody (MAb)-capture enzyme immunoassays (EIAs) were developed based on prME Karelia-94 (Siberian subtype) particles. Altogether, 140 human serum samples were tested using these assays, and the results were compared to those obtained with a commercial IgM EIA, an in-house μ-capture IgM assay based on baculovirus-expressed antigen, a commercial IgG EIA, and a hemagglutination inhibition test. Compared to reference enzyme-linked immunosorbent assays (ELISAs), the sensitivities of the generated μ-capture IgM SFV-prME and IgG MAb-capture SFV-prME EIAs were 97.4 to 100% and 98.7%, respectively, and the specificities of the two assays were 100%. IgM and IgG immunofluorescence assays (IFAs) were created based on Vero E6 cells transfected with the recombinant plasmid carrying the TBEV Karelia-94 prME glycoproteins. The IgM IFA was 100% concordant with the μ-capture IgM bac-prME ELISA. The IgG IFA sensitivity and specificity were 98.7% and 100%, respectively, compared to those of the commercial ELISA. In conclusion, the tests developed based on SFV replicon-driven expression of TBEV glycoproteins provide safe and robust alternatives for conducting TBEV serology.

Diagnosis of west nile virus human infections: overview and proposal of diagnostic protocols considering the results of external quality assessment studies

West Nile virus, genus Flavivirus, is transmitted between birds and occasionally other animals by ornithophilic mosquitoes. This virus also infects humans causing asymptomatic infections in about 85% of cases and <1% of clinical cases progress to severe neuroinvasive disease. The virus also presents a threat since most infections remain unapparent. However, the virus contained in blood and organs from asymptomatically infected donors can be transmitted to recipients of these infectious tissues. This paper reviews the presently available methods to achieve the laboratory diagnosis of West Nile virus infections in humans, discussing the most prominent advantages and disadvantages of each in light of the results obtained during four different External Quality Assessment studies carried out by the European Network for ‘Imported’ Viral Diseases (ENIVD).

Update on donor-derived infections in liver transplantation

Advances in surgical techniques, immunosuppressive medications, and robust infectious disease prophylaxis have resulted in liver transplantation becoming the treatment of choice for patients with end-stage liver disease and unresectable hepatocellular carcinoma. Nonetheless, organ transplantation is not without risk. Unexpected donor-derived disease transmission is a newly recognized risk that complicates approximately 0.2% of all organ transplants. We review the epidemiology of donor-derived infectious diseases and methods of risk mitigation with a focus on liver transplantation.

Acute West Nile virus neuroinvasive infections: cross-reactivity with dengue virus and tick-borne encephalitis virus

Cross-reactions in serology are common among flaviviruses. During the outbreak of West Nile virus (WNV) infections in Greece in 2010, WNV IgM-positive serum and cerebrospinal fluid samples were tested for the presence of IgM and IgG antibodies against Dengue virus (DENV) and tick-borne encephalitis virus. Higher cross-reactivity was observed in IgM antibodies between WNV and DENV; however, the index of the WNV antibodies was in all cases higher than that of the DENV antibodies. There is a need for caution when evaluating serologic results of flaviviral infections, while efforts have to be focused on the development of diagnostic assays with increased specificity.

Immune response to the West Nile virus in aged non-human primates

Background

Risk of encephalitis from West Nile virus (WNV) infection increases dramatically with age. Understanding the basis of this susceptibility requires development of suitable animal models. Here, we investigated the immune response to WNV in old non-human primates.

Methodology/Principal Findings

We investigated clinical, immunological and virological correlates of WNV infection in aging non-human primates. Aged (17–30yrs) and adult (6–9yrs) Rhesus macaques (RM) were challenged with WNV in the presence or the absence of the mosquito salivary gland extract (SGE) to approximate natural infection. None of the 26 animals exhibited clinical signs of the disease. Quantitative PCR suggested discrete and short-lived viremia, but infectious virus was never isolated. There was markedly increased, age-independent, proliferation of CD3⁻ non-B cells, followed by B-cell proliferation, which correlated to the loss of detectable WNV genomes. Moreover, animals primed with mosquito salivary gland extract exhibited reduced circulating WNV RNA. While we found the expected age-associated reduction in T cell proliferation, adaptive immunity did not correlate with infection outcome. That was further confirmed in a cohort of thymectomized and/or CD8 T-cell depleted Cynomolgus macaques (CM; N = 15), who also failed to develop WNV disease.

Conclusions/significance

Results are consistent with strong and age-independent innate resistance of macaques against WNV challenge. This animal model is therefore not suitable for vaccine and therapeutic testing against WNV. However, understanding the basis of their innate resistance against WNV in macaques could provide helpful clues to improve anti-WNV protection of older adults.

Poor performance of hepatitis C antibody tests in hospital patients in Uganda

Most hepatitis C testing in Uganda is performed using commercial rapid strip assays (RSA) to detect antibodies to hepatitis C virus (anti-HCV), rather than enzyme immunoassays (EIA). The prevalence of hepatitis C antibodies in a Ugandan hospital population was determined using both methods to test their accuracy using nucleic acid testing (NAT) as a reference. Sera from 380 consecutive hospitalized Ugandan patients were tested for anti-HCV using an RSA in Uganda, with subsequent automated third-generation EIA testing in the United States, followed by NAT. Recombinant immunoblot assays (RIBA) were used as a supplementary test to detect anti-HCV epitopes. Overall, anti-HCV was detected in 48/380 (13%) by one or both antibody tests. Anti-HCV was detected in 19 (5.0%) patients by RSA and in 33 (8.7%) patients by EIA; only four patients were anti-HCV positive by both methods. Fourteen of the 48 anti-HCV positive patients had detectable serum HCV RNA, 7 each by bDNA assay or by PCR. RSA detected only 7 of 14 HCV RNA positive sera. Of 29 RNA negative but anti-HCV positive patients tested by RIBA, only two were anti-HCV positive; 27 were anti-HCV negative or indeterminate. Anti-HCV testing by RSA and/or EIA was neither sensitive nor specific for detection of ongoing HCV infection in hospitalized Ugandan patients. Our findings underscore the importance of confirmatory nucleic acid testing, which, despite its increased cost, appears essential to manage African patients with HCV.

Evaluation of an enzyme immunoassay for detection of immunoglobulin M antibodies to West Nile virus and the importance of background subtraction in detecting nonspecific reactivity

Since the introduction of West Nile virus (WNV) in the United States in 1999, several assays have become commercially available to detect antibodies against WNV. Capture enzyme-linked immunosorbent assays (ELISAs) for the detection of WNV-specific immunoglobulin M (IgM) have been approved by the Food and Drug Administration for clinical testing and are available from Focus Diagnostics and PanBio, Inc. The Focus Diagnostics IgM capture ELISA utilizes a background subtraction protocol in order to detect nonspecific reactivity due to rheumatoid factor, heterophile antibodies, or other interfering substances. A background subtraction procedure is not currently recommended for the PanBio IgM capture ELISA. In previous experiments, we determined the agreement, sensitivity, and specificity of the PanBio first-generation IgM capture ELISA compared to an immunofluorescence assay and the Centers for Disease Control and Prevention's IgM capture ELISA. The PanBio assay has since been reformulated to improve the specificity of the assay. We evaluated the reformulated PanBio assay with and without an antigen subtraction procedure and compared the results to the Focus IgM capture ELISA. Agreement, sensitivity, and specificity of the PanBio assay were, respectively, 85%, 95%, and 76% without the subtraction protocol and 94%, 95%, and 93% with the subtraction protocol. In general, when the subtraction protocol was applied to the PanBio IgM capture ELISA, there was a reduction in some, but not all, false-positive results. We suggest that all WNV IgM assays be standardized with a procedure such as background subtraction to eliminate nonspecific reactivity that may cause false-positive results.

West Nile virus: recent trends in diagnosis and vaccine development

West Nile virus (WNV) is a mosquito-borne flavivirus, native to Africa, Europe, and Western Asia. In many respects, WNV is an outstanding example of a zoonotic pathogen that has leaped geographical barriers and can cause severe disease in human and horse. Before the emergence of WNV in the USA, only few methods of diagnosis were available. Recently, many changes in the fields of WN diagnosis and prevention have happened. This paper will review all these new tools. After a description of the main concerns in WNV and West Nile (WN) disease in humans and animals, this review will present the main available tests for serology and virology detection, from gold standard tests to more recently developed methods. Finally, licensed vaccines and candidate vaccines developed in humans, horses and birds will also been described.

West Nile virus immunoglobulin A (WNV IgA) detection in cerebrospinal fluid in relation to WNV IgG and IgM reactivity

BACKGROUND

Diagnostic criteria for neurologic involvement in WNV infection include WNV IgM detection in CSF; however, WNV IgM can persist in CSF >6 months. CSF IgA characterizes other flavivirus infections, but WNV IgA in CSF has not been evaluated. WNV IgM in CSF correlates with IgM in serum but the presence of WNV IgA in CSF compared to serum is unknown.

OBJECTIVES

Evaluate WNV IgA detection in CSF as a marker of WNV neuroinvasive infection, initially with samples pre-selected based on WNV IgG and IgM reactivity and subsequently with all available CSF samples submitted for WNV antibody testing over an entire WNV season.

STUDY DESIGN

Selected CSF samples and CSF/serum pairs previously tested for WNV IgG and IgM were assayed for WNV IgA. Subsequently, all available CSF samples tested for WNV antibodies during the 2005 season were tested for WNV IgA, including those where paired sera were available and tested for IgA, IgG and IgM.

RESULTS

For most samples, including paired CSF and serum, the IgA result qualitatively agreed with the IgM result, regardless of the IgG result.

CONCLUSION

IgA detection is equivalent to IgM detection as a marker of WNV infection in CSF.

Evaluations of commercial West Nile virus immunoglobulin G (IgG) and IgM enzyme immunoassays show the value of continuous validation

West Nile virus was introduced into the United States in 1999 and in only four seasons has become endemic east of the Rocky Mountains. Recently, immunoglobulin M (IgM)-capture enzyme immunoassays for the detection of West Nile virus-specific IgM and indirect IgG enzyme immunoassays for the detection of IgG antibodies against West Nile virus were made available from Focus Technologies and PANBIO, Inc. We evaluated these commercial IgG and IgM test systems and determined agreement, sensitivity, and specificity for the assays, compared to immunofluorescence assay and the Centers for Disease Control and Prevention's IgM-capture enzyme-linked immunosorbent assay (ELISA). Initially, the Focus and PANBIO IgM enzyme immunoassays had at least 95% agreement, sensitivity, and specificity, and, based on the 95% confidence intervals, both IgM-capture assays performed similarly. The IgG assays also performed well, although the Focus IgG assay demonstrated greater specificity (98.8%) and the PANBIO IgG assay demonstrated greater sensitivity (99.3%). However, for 400 samples consecutively submitted for West Nile virus antibody testing during 2 days of the 2003 West Nile virus season, agreement, clinical sensitivity, and clinical specificity were 93.1, 98.0, and 92.4%, respectively, for the PANBIO IgM assay and were 97.4, 100.0, and 97.1%, respectively, for the Focus IgM assay. The specificities observed in this second evaluation equates to an overall false-positivity rate of 6.3% in the PANBIO West Nile virus IgM-capture ELISA versus 2.5% with the Focus West Nile virus IgM-capture ELISA. This experience demonstrates the importance of continuously evaluating the performance of an assay in order to detect any changes in assay performance as the test population evolves.

Utility of the focus technologies west nile virus immunoglobulin M capture enzyme-linked immunosorbent assay for testing cerebrospinal fluid

Focus Technologies has developed an immunoglobulin M (IgM) capture enzyme-linked immunosorbent assay (ELISA) kit that utilizes recombinant West Nile virus (WNV) antigens to detect WNV IgM in serum. We evaluate here the utility of the kit for detecting WNV IgM in cerebrospinal fluid (CSF). The sensitivity was evaluated by using 52 CSF specimens from the 2002 WNV season that were positive in both the Public Health Service Laboratories WNV IgM ELISA and an in-house WNV IgM ELISA with native WNV antigen. The specificity was evaluated with two groups of specimens: (i). 73 CSF specimens submitted for in-house WNV IgM ELISA testing from February through April 2003 and yielding a negative WNV IgM result and (ii). 60 CSF specimens determined to be positive for another virus by PCR testing. Using these 185 CSF specimens at a screening dilution of 1:2, the kit was determined to be 100% sensitive and 100% specific. Endpoint titers were determined for 20 IgM-positive CSF specimens by testing serial twofold dilutions and ranged from 1:8 to 1:512. Index values (specimen absorbance value/calibrator absorbance value) for the screening dilution (1:2) showed no correlation with IgM titers, whereas index values for higher dilutions showed significant correlation with IgM titers. CSF screening dilutions of greater than 1:2 are not recommended, however, due to the risk of obtaining false-negative results. These findings show that the Focus Technologies WNV IgM capture ELISA, when utilized as recommended, offers accurate qualitative detection of WNV IgM in CSF specimens.