Development of a fluorescent-microsphere immunoassay for detection of antibodies specific to equine arteritis virus and comparison with the virus neutralization test

Development and validation of a pentaplex assay for the identification of antibodies against common viral diseases in cattle

Animal welfare and economic implications of infectious diseases in cattle demand an efficient surveillance as the foundation for control and eradication programmes. Bovine respiratory syncytial virus (BRSV), Parainfluenza virus type 3 (PI3V), Bovine herpes virus-1 (BoHV-1), Bovine viral diarrhoea virus (BVDV), and Enzootic bovine leukosis virus (EBLV) cause common and often underdiagnosed diseases in cattle that are endemic in most countries [1]. A hallmark of individual exposure to a viral pathogen is the presence of antibodies directed towards that virus. The aim of this study was to develop and validate a pentaplex assay to simultaneously detect and quantify antibodies against BRSV, PI3V, BoHV-1, BVDV and EBLV in serum, as an efficient tool to yield epidemiological data. Monoplex assays were initially developed using either complete BRSV or BoHV-1 viral lysates, or recombinant proteins for BVDV, EBLV or PI3V as capture antigens. In addition, 125 serum samples from unvaccinated cattle, which were classified as positive or negative for each of the viruses by commercial ELISA kits, were used for validation. Conditions established for the Luminex monoplex assays were adopted for the pentaplex assay. The accuracy, determined by the area under the ROC curve, was greater than 0.97, and assay diagnostic sensitivities and specificities were over 95 and 90%, respectively, for all antigens. Intra (r) and interassay (R) coefficients of variation were under 10 and 20 %, respectively. Selectivity towards target viruses was shown by binding inhibition assays where unbound viruses reduced fluorescence intensities. Diagnostic agreement for samples analysed simultaneously in the monoplex and multiplex assays was almost perfect. In conclusion, a highly sensitive pentaplex assay was validated for the simultaneous identification of antibodies directed against BVDV, BoHV-1, PI3V, BRSV and EBLV in serum. The developed pentaplex assay complies with performance characteristics established by international guidelines for diagnostic tests and may be used as a tool for the implementation of epidemiological surveillance.

Equine Arteritis Virus Elicits a Mucosal Antibody Response in the Reproductive Tract of Persistently Infected Stallions

Equine arteritis virus (EAV) has the ability to establish persistent infection in the reproductive tract of the stallion (carrier) and is continuously shed in its semen. We have recently demonstrated that EAV persists within stromal cells and a subset of lymphocytes in the stallion accessory sex glands in the presence of a significant local inflammatory response. In the present study, we demonstrated that EAV elicits a mucosal antibody response in the reproductive tract during persistent infection with homing of plasma cells into accessory sex glands. The EAV-specific immunoglobulin isotypes in seminal plasma included IgA, IgG1, IgG3/5, and IgG4/7. Interestingly, seminal plasma IgG1 and IgG4/7 possessed virus-neutralizing activity, while seminal plasma IgA and IgG3/5 did not. However, virus-neutralizing IgG1 and IgG4/7 in seminal plasma were not effective in preventing viral infectivity. In addition, the serological response was primarily mediated by virus-specific IgM and IgG1, while virus-specific serum IgA, IgG3/5, IgG4/7, and IgG6 isotype responses were not detected. This is the first report characterizing the immunoglobulin isotypes in equine serum and seminal plasma in response to EAV infection. The findings presented herein suggest that while a broader immunoglobulin isotype diversity is elicited in seminal plasma, EAV has the ability to persist in the reproductive tract, in spite of local mucosal antibody and inflammatory responses. This study provides further evidence that EAV employs complex immune evasion mechanisms during persistence in the reproductive tract that warrant further investigation.

Species-Specific Serological Detection for Schistosomiasis by Serine Protease Inhibitor (SERPIN) in Multiplex Assay

BACKGROUND

Both Schistosoma mansoni and Schistosoma haematobium cause schistosomiasis in sub-Saharan Africa. We assessed the diagnostic value of selected Schistosoma antigens for the development of a multiplex serological immunoassay for sero-epidemiological surveillance.

METHODOLOGY/PRINCIPAL FINDINGS

Diagnostic ability of recombinant antigens from S. mansoni and S. haematobium was assessed by Luminex multiplex immunoassay using plasma from school children in two areas of Kenya, endemic for different species of schistosomiasis. S. mansoni serine protease inhibitor (SERPIN) and Sm-RP26 showed significantly higher reactivity to patient plasma as compared to the control group. Sm-Filamin, Sm-GAPDH, Sm-GST, Sm-LAP1, Sm-LAP2, Sm-Sm31, Sm-Sm32 and Sm-Tropomyosin did not show difference in reactivity between S. mansoni infected and uninfected pupils. Sm-RP26 was cross-reactive to plasma from S. haematobium patients, whereas Sm-SERPIN was species-specific. Sh-SEPRIN was partially cross-reactive to S. mansoni infected patients. ROC analysis for Sm-RP26, Sm-SERPIN and Sh-SERPIN showed AUC values of 0.833, 0.888 and 0.947, respectively. Using Spearman's rank correlation coefficient analysis, we also found significant positive correlation between the number of excreted eggs and median fluorescence intensity (MFI) from the multiplex immunoassays for Sm-SERPIN (ρ = 0.430, p-value = 0.003) and Sh-SERPIN (ρ = 0.433, p-value = 0.006).

CONCLUSIONS/SIGNIFICANCE

Sm-SERPIN is a promising species-specific diagnostic antigen. Sh-SEPRIN was partially cross-reactive to S. mansoni infected patients. SERPINs showed correlation with the number of excreted eggs. These indicate prospects for inclusion of SERPINs in the multiplex serological immunoassay system.

Development of a multiplex fluorescence immunological assay for the simultaneous detection of antibodies against Cooperia oncophora, Dictyocaulus viviparus and Fasciola hepatica in cattle

Background

A major constraint for the effective control and management of helminth parasites is the lack of rapid, high-throughput, routine diagnostic tests to assess the health status of individual animals and herds and to identify the parasite species responsible for these helminthoses. The capability of a multiplex platform for the simultaneous detection of three pasture associated parasite species was evaluated and compared to existing ELISAs.

Methods

The recombinant antigens 14.2 kDa ES protein for Cooperia oncophora, major sperm protein for Dictyocaulus viviparus and Cathepsin L1 for Fasciola hepatica were recombinantly expressed either in Escherichia coli or Pichia pastoris. Antigens were covalently coupled onto magnetic beads. Optimal concentrations for coupling were determined following the examination of serum samples collected from experimentally mono-infected animals, before and after their infection with the target species. Absence of cross-reactivity was further determined with sera from calves mono-infected with Haemonchus contortus, Ostertagia ostertagi and Trichostrongylus colubriformis. Examination of negative serum samples was characterised by low median fluorescence intensity (MFI).

Results

Establishment of the optimal serum dilution of 1:200 was achieved for all three bead sets. Receiver Operating Characteristic analyses were performed to obtain cut-off MFI values for each parasite separately. Sensitivity and specificity at the chosen cut-off values were close to, or 100 % for all bead sets. Examination of serum samples collected on different days post infection from different animals showed a high reproducibility of the assays. Serum samples were additionally examined with two already established ELISAs, an in-house ELISA using the recombinant MSP as an antigen and a DRG ELISA using Cathepsin L1 for liver fluke. The results between the assays were compared and kappa tests revealed an overall good agreement.

Conclusions

A versatile bead-based assay using fluorescence detection (xMAP® technology) was developed to simultaneously detect antibodies against C. oncophora, D. viviparus and F. hepatica in cattle serum samples. This platform provides rapid, high-throughput results and is highly sensitive and specific in comparison to existing serological as well as coproscopical diagnostic techniques.

Serological surveillance development for tropical infectious diseases using simultaneous microsphere-based multiplex assays and finite mixture models

Background

A strategy to combat infectious diseases, including neglected tropical diseases (NTDs), will depend on the development of reliable epidemiological surveillance methods. To establish a simple and practical seroprevalence detection system, we developed a microsphere-based multiplex immunoassay system and evaluated utility using samples obtained in Kenya.

Methods

We developed a microsphere-based immuno-assay system to simultaneously measure the individual levels of plasma antibody (IgG) against 8 antigens derived from 6 pathogens: Entamoeba histolytica (C-IgL), Leishmania donovani (KRP42), Toxoplasma gondii (SAG1), Wuchereria bancrofti (SXP1), HIV (gag, gp120 and gp41), and Vibrio cholerae (cholera toxin). The assay system was validated using appropriate control samples. The assay system was applied for 3411 blood samples collected from the general population randomly selected from two health and demographic surveillance system (HDSS) cohorts in the coastal and western regions of Kenya. The immunoassay values distribution for each antigen was mathematically defined by a finite mixture model, and cut-off values were optimized.

Findings

Sensitivities and specificities for each antigen ranged between 71 and 100%. Seroprevalences for each pathogen from the Kwale and Mbita HDSS sites (respectively) were as follows: HIV, 3.0% and 20.1%; L. donovani, 12.6% and 17.3%; E. histolytica, 12.8% and 16.6%; and T. gondii, 30.9% and 28.2%. Seroprevalences of W. bancrofti and V. cholerae showed relatively high figures, especially among children. The results might be affected by immunological cross reactions between W. bancrofti-SXP1 and other parasitic infections; and cholera toxin and the enterotoxigenic E. coli (ETEC), respectively.

Interpretation

A microsphere-based multi-serological assay system can provide an opportunity to comprehensively grasp epidemiological features for NTDs. By adding pathogens and antigens of interest, optimized made-to-order high-quality programs can be established to utilize limited resources to effectively control NTDs in Africa.

Monitoring the distribution of neglected tropical diseases (NTDs) is a key to controlling their spread in Africa. Currently, such surveillance is conducted independently for each NTD. To tackle this problem, we developed a microsphere-based system to permit simultaneous measurement of IgG antibody levels for antigens from six infectious diseases: Entamoeba histolytica, Leishmania donovani, Toxoplasma gondii, Wuchereria bancrofti, HIV, and Vibrio cholerae. Using this system, we conducted a serological survey using two health and demographic surveillance system (HDSS) areas in coastal and western Kenya. We randomly selected 4,600 individuals according to sex and age group, of whom 3411 agreed to participate in the study. Mathematical analyses of the distributions of the participants' reactivity to each antigen and the reactivity of the sero-positive and -negative controls indicated that this system could be used to monitor infections, especially, those associated with HIV, filariasis, toxoplasmosis, leishmaniasis, and amebiasis. For the practical development and eventual implementation of actual programs in Africa, pathogens and antigens of interest can be added to optimize made-to-order monitoring programs.

Equine arteritis virus

Equine arteritis virus (EAV) is the causative agent of equine viral arteritis (EVA), a respiratory and reproductive disease of equids. There has been significant recent progress in understanding the molecular biology of EAV and the pathogenesis of its infection in horses. In particular, the use of contemporary genomic techniques, along with the development and reverse genetic manipulation of infectious cDNA clones of several strains of EAV, has generated significant novel information regarding the basic molecular biology of the virus. Therefore, the objective of this review is to summarize current understanding of EAV virion architecture, replication, evolution, molecular epidemiology and genetic variation, pathogenesis including the influence of host genetics on disease susceptibility, host immune response, and potential vaccination and treatment strategies.

Opportunities for bead-based multiplex assays in veterinary diagnostic laboratories

Bead-based multiplex assays (BBMAs) are applicable for high throughput, simultaneous detection of multiple analytes in solution (from several to 50–500 analytes within a single, small sample volume). Currently, few assays are commercially available for veterinary applications, but they are available to identify and measure various cytokines, growth factors and their receptors, inflammatory proteins, kinases and inhibitors, neurobiology proteins, and pathogens and antibodies in human beings, nonhuman primates, and rodent species. In veterinary medicine, various nucleic acid and protein-coupled beads can be used in, or for the development of, antigen and antibody BBMAs, with the advantage that more data can be collected using approximately the same amount of labor as used for other antigen and antibody assays. Veterinary-related BBMAs could be used for detection of pathogens, genotyping, measurement of hormone levels, and in disease surveillance and vaccine assessment. It will be important to evaluate whether BBMAs are “fit for purpose,” how costs and efficiencies compare between assays, which assays are published or commercially available for specific veterinary applications, and what procedures are involved in the development of the assays. It is expected that many veterinary-related BBMAs will be published and/or become commercially available in the next few years. The current review summarizes the BBMA technology and some of the currently available BBMAs developed for veterinary settings. Some of the human diagnostic BBMAs are also described, providing an example of possible templates for future development of new veterinary-related BBMAs.

New approaches in microbial pathogen detection

Viruses are common causes of foodborne outbreaks. Viral diseases have low fatality rates but transmission to humans via food is important due to the high probability of consuming fecally contaminated food or water because of poor food handling. Because of the low infectious doses of some foodborne viruses, there is a need for standardization and the development of new sensitive methods for detecting viruses. The focus is on molecular and non-molecular approaches, and emerging methods for the detection of foodborne viruses. The detection of noroviruses, hepatitis A and E viruses, rotaviruses and adenoviruses will be discussed. The chapter will conclude with insights into future research directions.

A bead-based suspension array for the serological detection of Trichinella in pigs

The feasibility of using bead-based suspension arrays to detect serological evidence of Trichinella in pigs was assessed. Trichinella spiralis excretory-secretory antigen was covalently coupled to paramagnetic beads and used to bind serum antibodies, which were subsequently detected using anti-swine antibody. The assay was evaluated by testing pig sera from farms where trichinellosis was endemic and comparing the results with those obtained using two commercially available ELISAs. With cut-offs established by receiver operating characteristic (ROC) analysis, digestion-negative sera from a Trichinella-free population of pigs were deemed seronegative. When anti-swine antibody was replaced with protein A/G, higher test sensitivity (94% vs. 88%) at similar test specificity (95%), was achieved. The potential use of this assay in species other than swine was also demonstrated by testing human sera.

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.

Multiplex method for simultaneous serological detection of porcine reproductive and respiratory syndrome virus and porcine circovirus type 2

Porcine circovirus type 2 (PCV2) and porcine reproductive and respiratory syndrome virus (PRRSV) are major contributors to the porcine respiratory disease complex (PRDC). Routine serological diagnosis and surveillance play an important role in the prevention of PRDC, as it is a leading cause of economic losses to the swine industry. We herein describe an advanced microsphere-based immunoassay that permits the simultaneous detection of antibodies to PCV2 and PRRSV, thereby reducing the time and effort involved in testing. Recombinant PRRSV nucleoprotein antigen and the PCV2 capsid antigen were coupled to fluorophore-dyed beads with distinct spectral addresses. Weekly serum samples from 72 pigs that were experimentally exposed to either PCV2, PRRSV, or both PCV2 and PRRSV were used to validate the microbead assay (MBA) in comparison with the "gold standard" enzyme-linked immunosorbent assays. The kinetics of the PCV2- and PRRSV-specific antibody responses measured by the microbead assay were comparable to those of the standard assays; Spearman's rank correlations were 0.72 (P < 0.001) for PRRSV and 0.80 (P < 0.001) for PCV2. Diagnostic sensitivity and specificity were determined using field sera whose positive or negative status was determined by the standard tests. The diagnostic sensitivity and specificity were both 98% for PCV2 and were 91% and 93%, respectively, for PRRSV (kappa coefficients, 0.85 and 0.67 for PCV2 and PRRSV, respectively). Multiplexing did not interfere with assay performance or diagnostic sensitivity. Therefore, the described study demonstrates proof of concept for the development of more versatile and economical microbead array-based multiplex serological test panels for veterinary use.

Characterization of equine humoral antibody response to the nonstructural proteins of equine arteritis virus

Equine arteritis virus (EAV) replicase consists of two polyproteins (pp1a and pp1ab) that are encoded by open reading frames (ORFs) 1a and 1b of the viral genome. These two replicase polyproteins are posttranslationally processed by three ORF 1a-encoded proteinases to yield at least 13 nonstructural proteins (nsp1 to nsp12, including nsp7α and 7β). These nsps are expressed in EAV-infected cells, but the equine immune response they induce has not been studied. Therefore, the primary purpose of this study was to evaluate the humoral immune response of horses to each of the nsps following EAV infection. Individual nsp coding regions were cloned and expressed in both mammalian and bacterial expression systems. Each recombinant protein was used in an immunoprecipitation assay with equine serum samples from horses (n = 3) that were experimentally infected with three different EAV strains (VB, KY77, and KY84), from stallions (n = 4) that were persistently infected with EAV, and from horses (n = 4) that were vaccinated with the modified live-virus (MLV) vaccine strain. Subsequently, protein-antibody complexes were subjected to Western immunoblotting analysis with individual nsp-specific rabbit antisera, mouse anti-His antibody, or anti-FLAG tag antibody. Nsp2, nsp4, nsp5, and nsp12 were immunoprecipitated by most of the sera from experimentally or persistently infected horses, while sera from vaccinated horses did not react with nsp5 and reacted weakly with nsp4. However, serum samples from vaccinated horses were able to immunoprecipitate nsp2 and nsp12 proteins consistently. Information from this study will assist ongoing efforts to develop improved methods for the serologic diagnosis of EAV infection in horses.

A microsphere-based immunoassay for rapid and sensitive detection of bovine viral diarrhoea virus antibodies

This study describes a novel blocking microsphere-based immunoassay for highly sensitive and specific detection of antibodies against bovine viral diarrhoea virus (BVDV). The intra- and inter-assay variability are 4.9% and less than 7%, respectively, and variability of bead conjugations is less than 6.6%. The diagnostic performance of the assay was evaluated by testing a total of 509 serum samples. Based on a negative/positive cut-off value of 30.3%, the assay has a sensitivity of 99.4% and a specificity of 98.3% relative to ELISA. The new microsphere immunoassay provides an alternative to conventional ELISA systems and can be used for high-throughput screening in the BVD control programmes.

A multiplexed immunoassay for detection of antibodies against avian influenza virus

Avian influenza (AI) is a highly contagious disease in poultry and outbreaks can have dramatic economic and health implications. For effective disease surveillance, rapid and sensitive assays are needed to detect antibodies against AI virus (AIV) proteins. In this study, we report the development of a multiplexed fluorescence microsphere immunoassay (FMIA) for detection of antibodies against AIV proteins in poultry. Recombinant nucleoprotein (NP), matrix protein (M1), and non-structural protein 1 (NS1) were expressed using a baculovirus expression system, purified and covalently coupled to fluorescent xMAP microspheres. Using these reagents, a triplex bead assay was developed for the Luminex platform. The assay displayed minimal cross reactivity when screened against a panel of reference sera raised against common avian viruses. For detection of anti-NP antibodies, the sensitivity and specificity of the assay were comparable to a commercially available ELISA. The assay was also employed to investigate the early kinetics of antibody response in chickens infected with AIV. Our results suggest that NP should be the protein of choice when detecting AI infections in commercial chickens, as the immune response was higher and persisted longer than that of M1 and NS1 proteins. This report provides a framework from which a more robust assay could be developed to profile exposure to many AIV subtypes in a single test.

Equine viral arteritis: current status and prevention

Recently, there has been increased interest in equine viral arteritis (EVA) among veterinarians and horse owners. Outbreaks of the disease were identified initially in New Mexico, USA in 2006, and in the Normandy region of France in the summer of 2007. Both occurrences were associated with AI of cool-shipped semen. Each was linked to respiratory illness, neonatal death, abortion, development of carrier stallions, and cancellation of equestrian events. In light of the increased interest, this paper will present a brief case history, followed by a review addressing common concerns regarding EVA, current status, and control and prevention strategies, including vaccination, and recommended bio-security measures.