Evaluation of a competitive ELISA for antibody detection against avian influenza virus

Highly sensitive and label-free detection of influenza H5N1 viral proteins using affinity peptide and porous BSA/MXene nanocomposite electrode

Influenza viruses are known to cause pandemic flu through inter-human and animal-to-human transmissions. Neuraminidase (NA), which is a surface glycoprotein of both influenza A and B viruses, is a minor immunogenic determinant; however, it has been proposed as an ideal candidate for a real testing. We successfully identified an affinity peptide which is specific to the influenza H5N1 virus NA via phage display technique and observed initially its binding affinities using enzyme-linked immunosorbent assay (ELISA). In addition, four synthetic peptides were chemically synthesized to develop an affinity peptide-based electrochemical biosensing system. Among all peptides tested, INA BP2 was selected as a potential candidate and subjected to square-wave voltammetry (SWV) for evaluating their detection performance. To enhance analytical performance, a three-dimensional porous bovine serum albumin (BSA)-MXene (BSA/MXene) matrix was applied. The surface morphology of the BSA/MXene film-deposited electrode was analyzed using X-ray photoelectron spectroscopy (XPS), field-emission scanning electron microscopy (FE-SEM), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Using SWV measurement, the BSA/MXene nanocomposite-based peptide sensor exhibited significant the dissociation constant (K_d = 9.34 ± 1.20 nM) and the limit of detection (LOD, 0.098 nM), resulting in good reproducibility, stability and recovery, even in the presence with spiked human plasma. These results demonstrate an alternative way of new bioanalytical sensing platform for developing more desirable sensitivity in other virus detection.

Pathogenesis of Avian Influenza Virus Subtype H9N2 in Turkeys and Evaluation of Inactivated Vaccine Efficacy

Avian influenza H9N2 viruses circulate in all types of poultry species, including turkeys, and cause significant losses for the poultry industry in many parts of the word. The aim of this study was to assess the pathogenesis of the Moroccan avian influenza virus (AIV) H9N2 under experimental conditions in turkeys and the protection efficacy of an inactivated commercial vaccine against AIV H9N2. Unvaccinated turkeys showed marked depression sinusitis, respiratory distress characterized by bronchiolar and tracheal rales of moderate severity, and a mortality rate of 50%. Postmortem examinations of dead and euthanatized birds revealed the presence of fibrinous tracheitis and airsacculitis lesions. Vaccination reduced the mortality rate to 20%. Vaccinated birds recovered at day 10 postchallenge, and only 12.5% (1/8) and 37.5% of birds still displayed fibrinous and nonfibrinous airsacculitis lesions, respectively, at day 15 postinoculation. Viral shedding in cloacal and tracheal swabs was lower in vaccinated than in control birds. Although viral RNA was detected in the cloacal swabs of all unvaccinated turkeys at day 3 postinoculation, only 50% of the vaccinated turkeys were positive for virus detection. At day 11 postinoculation, no viral RNA was detected in oropharyngeal swabs of vaccinated turkeys, whereas 40% of the unvaccinated turkeys were still shedding virus.

Evaluating the Effect of the Within-Flock Disease Transmission Rate on Premovement Active Surveillance in Low Pathogenicity Avian Influenza-Infected Flocks

Premovement active surveillance for low pathogenicity avian influenza (LPAI) may be a useful risk management tool for producers during high-risk periods, such as during an LPAI outbreak, or in areas where there is a recognized high risk for LPAI spread. The effectiveness of three active-surveillance protocols in mitigating LPAI spread risk related to the movement of spent broiler breeders to processing was evaluated in this study. Each protocol differed in the amount of real-time reverse transcription polymerase chain reaction (RRT-PCR) and serology testing conducted. The protocols were evaluated with the use of disease transmission and active surveillance simulation models parametrized specifically for broiler breeders to estimate the probability of detecting a current or past infection and the mean proportion of infectious birds at the time of sampling in houses where the infection remains undetected at the time of movement after exposure to the virus. The two values were estimated considering flock infection for 1-28 days prior to the day of scheduled movement. A distribution for the adequate contact rate, a parameter that controls the rate of within-house spread in the disease transmission model, was estimated for this study by a novel forward simulation approach with the use of serology data from three LPAI-infected broiler breeder flocks in the United States. The estimated distribution suggests that the lower contact-rate estimates from previously published studies were not a good fit for the serology results observed in these U.S. flocks, though considerable uncertainty remains in the parameter estimate. The results for the probability of detection and mean proportion of infectious, undetected birds suggest that RRT-PCR testing is most beneficial during the early stages of infection postexposure, and serology testing is most beneficial during the later stages of infection, results that are expected to hold for flocks outside the United States as well. Thus, protocols that combine RRT-PCR and serology testing can offer a more balanced approach with good performance over the disease course in a flock.

EVALUATION OF A COMMERCIAL COMPETITIVE ENZYME-LINKED IMMUNOSORBENT ASSAY FOR DETECTION OF AVIAN INFLUENZA VIRUS SUBTYPE H5 ANTIBODIES IN ZOO BIRDS

The hemagglutination inhibition (HI) test is the current gold standard for detecting antibodies to avian influenza virus (AIV). Enzyme-linked immunosorbent assays (ELISAs) have been explored for use in poultry and certain wild bird species because of high efficiency and lower cost. This study compared a commercial ELISA for detection of AIV subtype H5 antibodies with HI test of 572 serum samples from zoo birds. There was no significant difference between the results of the two tests when statistically compared by a McNemar χ² test (P = 0.86) and assessment of κ (κ = 0.87). With a specificity of 94.2% (95% confidence interval [CI], 0.92-0.97), a sensitivity of 93.9% (95% CI, 0.91-0.97), and an excellent correlation between the two tests, this ELISA can be recommended as an alternative to the HI test for preliminary screening of zoo bird sera for antibodies to AIV subtype H5.

Evidence of pandemic H1N1 influenza exposure in dogs and cats, Thailand: A serological survey

Influenza A virus causes respiratory disease in both humans and animals. In this study, a survey of influenza A antibodies in domestic dogs and cats was conducted in 47 animal shelters in 19 provinces of Thailand from September 2011 to September 2014. One thousand and eleven serum samples were collected from 932 dogs and 79 cats. Serum samples were tested for influenza A antibodies using a multi-species competitive NP-ELISA and haemagglutination inhibition (HI) assay. The NP-ELISA results showed that 0.97% (9/932) of dogs were positive, but all cat samples were negative. The HI test against pandemic H1N1, human H3N2 and canine H3N2 showed that 0.64% (6/932) and 1.20% (1/79) of dogs and cats were positive, respectively. It is noted that all six serum samples (5 dogs and 1 cat) had antibodies against pandemic H1N1. In summary, a serological survey revealed the evidence of pandemic H1N1 influenza exposure in both dogs and cats in the shelters in Thailand.

User-friendly point-of-care detection of influenza A (H1N1) virus using light guide in three-dimensional photonic crystal

This paper proposes a user-friendly and highly sensitive detection method for influenza A (H1N1) virus using the cooperation of quantum dot (Qdot)-aptamer beacons and light guide in a three-dimensional (3D) photonic crystal (PC). For easy use, we present a fluorescent probe-based 'OFF-ON' detection protocol. First, a mixture composed of Qdot-aptamer beacons and dark quencher-labeled guard DNA (G-DNA) was prepared. It initially quenched the fluorescent signals to significantly low intensity, i.e., 'OFF' state. Then, the influenza A (H1N1) virus preferentially bound to the aptamer and G-DNA was released, so that the fluorescent signal was restored and biosensor turned to 'ON' state. The restored fluorescence signal changed quantitatively according to the concentration of the target influenza A (H1N1) virus. Owing to the light guide of the 3D nanoporous PC structure, we achieved high sensitivity with ultra-low limit of detection (LOD) of 138 pg mL-1 and high selectivity over other species of influenza A virus and biomolecules. Additionally, with the benefit of enhanced output fluorescent signals, the target virus could be easily detected with a low-cost and portable home-made setup (total cost of only 20 US dollars) and a built-in camera in a smartphone.

Serological evidence of H5-subtype influenza A virus infection in indigenous avian and mammalian species in Korea

In Korea, H5-subtype highly pathogenic avian influenza (HPAI) has caused huge economic losses in poultry farms through outbreaks of H5N1 since 2003, H5N8 since 2013 and H5N6 since 2016. Although it was reported that long-distance migratory birds may play a major role in the global spread of avian influenza viruses (AIVs), transmission from such birds to poultry has not been confirmed. Intermediate hosts in the wild also may be a potential factor in viral transmission. Therefore, a total of 367 serum samples from wild animals were collected near major migratory bird habitats from 2011 to 2016 and tested by AIV-specific blocking ELISA and hemagglutination inhibition (HI) test. Two mammalian and eight avian species were seropositive according to the ELISA test. Among these, two mammalian (Hydropotes inermis and Prionailurus bengalensis) and three avian (Aegypius monachus, Cygnus cygnus, and Bubo bubo) species showed high HI titres (> 1,280) against one or two H5-subtype AIVs. As H. inermis (water deer), P. bengalensis (leopard cat), and B. bubo (Eurasian eagle owl) are indigenous animals in Korea, evidence of H5-subtype AIV in these animals implies that continuous monitoring of indigenous animals should be followed to understand interspecies transmission ecology of H5-subtype influenza viruses.

Development and standardization of an in-house indirect ELISA for detection of duck antibody to fowl cholera

Serological tests, such as agglutination and indirect hemagglutination assay (IHA), have been used to identify antibodies against Pasteurella multocida in poultry sera, but none are highly sensitive. An enzyme-linked immunosorbent assays (ELISA) has been used with varying degrees of success in attempts to monitor seroconversion in vaccinated poultry, but are not suitable for diagnosis. Commercial ELISA kits are available for chickens and turkeys, but not for ducks. The present study reports development and standardization of an in-house indirect ELISA for detection of duck antibody to fowl cholera. The characteristics of ELISA and IHA were analyzed using a one population Bayesian model assuming conditional dependence between the two diagnostic tests. An in-house indirect ELISA was developed using a heat extract antigen of P. multocida strain X-73 as a coating antigen and horseradish peroxidase conjugated goat anti-duck IgG antibody (dIgG-HRP). The checkerboard titration method was done using sera from ducks immunized with P. multocida bacterin as positive sera and 1day old duckling sera as negative sera. The heat extract antigen at 1μg/ml, sample serum at a dilution of 1:100, and dIgG-HRP 1:2000 were optimal concentrations for the assay. The cut-off value was 0.200. Of the duck sera, 89.05% (244/274) were considered seropositive by ELISA. Estimates for sensitivity and specificity of ELISA were higher than prior values with medians of 94.7% [95% posterior probability interval (PPI)=89.6-98.2%] and 87.2% (PPI=68.2-98.3%). Estimates for sensitivity of IHA were lower than prior values (median=97.6, PPI=93.2-99.7%) while the specificity was close to the prior value (median=76.5, PPI=65.8-85.4%). This finding suggests that an in-house indirect ELISA can be used to detect duck antibody to fowl cholera.

Multiplex one-step Real-time PCR by Taqman-MGB method for rapid detection of pan and H5 subtype avian influenza viruses

Avian influenza virus (AIV) can infect a variety of avian species and mammals, leading to severe economic losses in poultry industry and posing a substantial threat to public health. Currently, traditional virus isolation and identification is inadequate for the early diagnosis because of its labor-intensive and time-consuming features. Real-time RT-PCR (RRT-PCR) is an ideal method for the detection of AIV since it is highly specific, sensitive and rapid. In addition, as the new quencher MGB is used in RRT-PCR, it only needs shorter probe and helps the binding of target gene and probe. In this study, a pan-AIV RRT-PCR for the detection of all AIVs and H5-AIV RRT-PCR for detection of H5 AIV based on NP gene of AIV and HA gene of H5 AIV were successfully established using Taqman-MGB method. We tested 14 AIV strains in total and the results showed that the pan-AIV RRT-PCR can detect AIV of various HA subtypes and the H5-AIV RRT-PCR can detect H5 AIV circulating in poultry in China in recent three years, including H5 viruses of clade 7.2, clade 2.3.4.4 and clade 2.3.2.1. Furthermore, the multiplex detection limit for pan-AIV and H5-AIV RRT-PCR was 5 copies per reaction. When this multiplex method was applied in the detection of experimental and live poultry market samples, the detection rates of pan-AIV and H5 AIV in RRT-PCR were both higher than the routine virus isolation method with embryonated chicken eggs. The multiplex RRT-PCR method established in our study showed high sensitivity, reproducibility and specificity, suggesting the promising application of our method for surveillance of both pan AIV and prevalent H5 AIV in live poultry markets and clinical samples.

Serological Survey for Avian Influenza in Turkeys in Three States of Southwest Nigeria

Since the first outbreak of avian influenza (AI) in Nigeria in 2006, there has been continuous monitoring of the disease in chickens with little attention given to turkeys. As part of on-going surveillance for AI in southwest Nigeria, we used a competitive ELISA to detect anti-AI virus antibodies in 520 turkey sera obtained from poultry farms in Oyo, Osun, and Ondo states while haemagglutination inhibiting antibodies against low pathogenic AI viruses (LPAIVs) were detected using H3N8 and H5N2 subtype-specific antigens. The overall seroprevalence obtained by ELISA was 4.4% (23/520). Of the 23 ELISA-positive samples, 18 were positive for anti-AIV H3N8 antibodies only and four were positive for both anti-AIV H3N8 and H5N2 antibodies indicating a mixed infection, while five were negative for antibodies to either of the two AIV subtypes. Considering that turkeys have been implicated as a mixing vessel for generating influenza virus reassortants of human and avian origin, the detection of antibodies to LPAIV H3N8 and H5N2 in these turkeys is of public health concern. We advocate further studies to determine the potential role of turkeys in the zoonotic transmission of AIVs in Nigeria. Additionally, the practice of rearing turkeys with chickens should be discouraged.

Differential innate responses of chickens and ducks to low-pathogenic avian influenza

Ducks and chickens are hosts of avian influenza virus, each with distinctive responses to infection. To understand these differences, we characterized the innate immune response to low-pathogenicity avian influenza virus H7N1 infection in chickens and ducks. Viral RNA was detected in the lungs of chickens from day 0.8 to 7, in ducks mainly at day 4. In both species, viral RNA was detected in the bursa and gut. Infection in chickens resulted in up-regulation of interferon (IFN)-α and IFN-β mRNA, while in the ducks IFN-γ mRNA was strongly up-regulated in the lung and bursa. In chickens and ducks, all investigated pathogen recognition receptor (PRR) mRNAs were up-regulated; however, in the chicken lung Toll-like receptor (TLR)7 and melanoma differentiation-associated protein (MDA)-5 mRNA were strongly induced. TLR3, TLR7 and MDA-5 responses correlated with IFN-α and IFN-β responses in chickens, but in ducks a correlation between IFN-α and TLR7, retinoic acid-inducible gene-I and MDA-5 was absent. We studied the responses of duck and chicken splenocytes to poly(I:C) and R848 analogues to analyse the regulation of PRRs without the interfering mechanisms of the influenza virus. This revealed IFN-α and IFN-γ responses in both species. MDA-5 was only strongly up-regulated in chicken splenocytes, in which time-related PRR responses correlated with the IFN-α and IFN-β response. This correlation was absent in duck splenocytes. In conclusion, chickens and ducks differ in induction of MDA-5, TLR7 and IFN-α mRNA after an influenza virus infection in vivo and after in vitro stimulation with TLR antagonists.

Comparative analysis of virulence of a novel, avian-origin H3N2 canine influenza virus in various host species

A novel avian-origin H3N2 canine influenza A virus (CIV) that showed high sequence similarities in hemagglutinin and neuraminidase genes with those of non-pathogenic avian influenza viruses was isolated in our routine surveillance program in South Korea. We previously reported that the pathogenicity of this strain could be reproduced in dogs and cats. In the present study, the host tropism of H3N2 CIV was examined by experimental inoculation into several host species, including chickens, pigs, mice, guinea pigs, and ferrets. The CIV infection resulted in no overt symptoms of disease in these host species. However, sero-conversion, virus shedding, and gross and histopathologic lung lesions were observed in guinea pig and ferrets but not in pigs, or mice. Based on the genetic similarity of our H3N2 CIV with currently circulating avian influenza viruses and the presence of α-2,3-linked rather than α-2,6-linked sialic acid receptors in the respiratory tract of dogs, we believed that this strain of CIV would have avian virus-like receptor specificity, but that seems to be contrary to our findings in the present study. Further studies are needed to determine the co-receptors of hemagglutinin or post-attachment factors related to virus internalization or pathogenesis in other animals.

Avian influenza: virology, diagnosis and surveillance

Avian influenza virus (AIV) is the causative agent of a zoonotic disease that affects populations worldwide with often devastating economic and health consequences. Most AIV subtypes cause little or no disease in waterfowl, but outbreaks in poultry can be associated with high mortality. Although transmission of AIV to humans occurs rarely and is strain dependent, the virus has the ability to mutate or reassort into a form that triggers a life-threatening infection. The constant emergence of new influenza strains makes it particularly challenging to predict the behavior, spread, virulence or potential for human-to-human transmission. Because it is difficult to anticipate which viral strain or what location will initiate the next pandemic, it is difficult to prepare for that event. However, rigorous implementation of biosecurity, vaccination and education programs can minimize the threat of AIV. Global surveillance programs help record and identify newly evolving and potentially pandemic strains harbored by the reservoir host.

An enzyme-linked immunosorbent assay for detection of avian influenza virus subtypes H5 and H7 antibodies

Background

Avian influenza virus (AIV) subtypes H5 and H7 attracts particular attention because of the risk of their potential pathogenicity in poultry. The haemagglutination inhibition (HI) test is widely used as subtype specific test for serological diagnostics despite the laborious nature of this method. However, enzyme-linked immunosorbent assays (ELISAs) are being explored as an alternative test method.

H5 and H7 specific monoclonal antibodies were experimentally raised and used in the development of inhibition ELISAs for detection of serological response specifically directed against AIV subtypes H5 and H7. The ELISAs were evaluated with polyclonal chicken anti-AIV antibodies against AIV subtypes: H1N2, H5N2, H5N7, H7N1, H7N7, H9N9, H10N4 and H16N3.

Results

Both the H5 and H7 ELISA proved to have a high sensitivity and specificity and the ELISAs detected H5 and H7 antibodies earlier during experimental infection than the HI test did. The reproducibility of the ELISA’s performed at different times was high with Pearson correlation coefficients of 0.96-0.98.

Conclusions

The ELISAs are a potential alternative to the HI test for screening of large amounts of avian sera, although only experimental sera were tested in this study.

Detection of genetic markers related to high pathogenicity in influenza by SERS

We have developed a method for the detection of genetic markers associated with high pathogenicity in influenza. The assay consists of an array of 5'-thiolated ssDNA oligonucleotides immobilized on the surface of a Ag nanorod substrate that serve as capture probes for the detection of synthetic RNA sequences coding for a genetic mutation in the influenza PB1-F2 protein. Hybridization of the DNA probes to their complementary RNA sequences was detected using surface-enhanced Raman spectroscopy (SERS). Multivariate statistical analysis was used to differentiate the spectra of the complementary DNA probe-RNA target hybrids from those of the non-complementary DNA probes containing a single base pair polymorphism. Hierarchical cluster analysis (HCA) was able to distinguish with 100% accuracy the spectra of the complementary DNA probe-RNA target from the spectra of the immobilized DNA probes alone, or the DNA probes incubated with non-complementary RNA sequences. Linearity of response and limits of sensitivity of the SERS-based assays were determined using a partial least squares (PLS) regression model; detection limits computed by PLS was determined to be ~10 nM. The binding affinity of the DNA probes to their complementary RNA sequences was confirmed using enzyme-linked immunosorbent assay (ELISA); however, the detection limits observed using ELISA were approximately 10× higher (~100 nM) than those determined by PLS analysis of the SERS spectra.

Evaluation of a commercial ELISA for H5 low pathogenic avian influenza virus antibody detection in duck sera using Bayesian methods

Following the emergence of highly pathogenic avian influenza (AI), active surveillance of infections due to the H5 and H7 subtypes in poultry has increased and been made compulsory in Europe since 2002, by means of annual serological surveys using the haemagglutination inhibition (HI) test. Domestic anseriforms, particularly ducks and geese, are more frequently infected by H5 low pathogenic AI virus, often subclinically, and represent a threat for other terrestrial poultry. 1783 sera, mainly from ducks, have been used to evaluate and compare a commercial ELISA kit detecting H5 antibodies with the currently recommended HI test. Different approaches to calculating specificity and sensitivity have been used, including the original Bayesian method. Results were similar when data were analyzed at the individual and batch levels, and when using different methods of calculation. However, results showed that H5 ELISA had both a higher sensitivity and a lower specificity than the HI test. Given that sensitivity is the most important factor for a screening test, H5 ELISA could therefore be recommended for AI surveillance, followed in cases of positivity by molecular tests aimed at detecting the virus gene.

Risk factors and characteristics of low pathogenic avian influenza virus isolated from commercial poultry in Tunisia

Objective

Estimate the seroprevalence of influenza A virus in various commercial poultry farms and evaluate specific risk factors as well as analyze their genetic nature using molecular assays.

Materials and Methods

This report summarizes the findings of a national survey realized from October 2010 to May 2011 on 800 flocks in 20 governorates. Serum samples were screened for the presence of specific influenza virus antibodies using cELISA test. Additionally, swab samples were tested by real time and conventional RT-PCR and compared with results obtained by others assays. Phylogenetic and genetic analyses of the glycoproteins were established for some strains.

Results

Out of the 800 chicken and turkey flocks tested by cELISA, 223 showed positive anti-NP antibodies (28.7%, 95% CI: 25.6–32.1). Significantly higher seroprevalence was found among the coastal areas compared to inland and during the autumn and winter. Broiler flocks showed significantly lower seroprevalence than layers and broiler breeders. The influenza virus infection prevalence increased after the laying phase among layer flocks. In addition, AIV seropositivity was significantly associated with low biosecurity measures. The Ag EIA and rRT-PCR tests revealed significantly higher numbers of AI positive samples as compared to cell cultures or egg inoculation. All new strains were subtyped as H9N2 by real time and conventional RT-PCR. Drift mutations, addition or deletion of glycosylation sites were likely to have occurred in the HA and NA glycoproteins of Tunisian strains resulting in multiple new amino acid substitutions. This fact may reflect different evolutionary pressures affecting these glycoproteins. The role of these newly detected substitutions should be tested.

Conclusion

Our findings highlight the potential risk of AIV to avian health. Strict enforcement of biosecurity measures and possible vaccination of all poultry flocks with continuous monitoring of poultry stations may ensure reduction of AIV prevalence and avoid emergence of more pathogenic strains.

Adaptations of a competitive enzyme-linked immunosorbent assays for the detection of antibodies to influenza a virus in horse sera for use in wild aquatic birds

We applied a competitive enzyme-linked immunosorbent assay for the detection of antibodies for influenza A in equine sera to their detection in sera from wild aquatic birds. Suboptimal results were obtained for the optical density (OD) of the monoclonal antibody (MAb) control and reproducibility between duplicate analyses in the initial assessment. It was therefore necessary to modify the assay to deliver increased reliability and reproducibility while maintaining adequate sensitivity. We optimized reagent concentrations to obtain optimal OD values (close to 2) for the monoclonal antibody control and used 2, 2'-Azino-bis: 3-Benzthiazoline-6-Sulphonic Acid as an alternative chromogen to potentially reduce variability in duplicate analyses. The original assay was compared with the optimized versions, with and without post coating, for the detection of avian influenza viral antibodies in 240 sera obtained from wild plumed whistling ducks. A separate analytical sensitivity study on diluted positive field sera of plumed whistling ducks and a test of antigen stability after post coating were also performed. Some quantitative differences were detected between the original and modified assays. The original assay recorded higher percentage inhibition results which were potentially indicative of increased sensitivity. However, when reagent concentrations were increased in the original assay to the same levels as used in the modified versions, there were no quantitative differences for practical purposes. The original assay produced a median (OD) value of 0.81 for the (MAb) controls that is at the limit of acceptability. By contrast, the modified assays always produced acceptable optical density values for MAb controls. Our overall results indicated the modified assays were potentially more reliable (OD values close to 2), and of adequate sensitivity compared to the original assay in the detection of avian influenza viral antibodies in wild bird sera. Although further optimization of antigen and MAb concentrations should also be considered to increase the sensitivity of a modified assay, while maintaining acceptable optical density values for the MAb control. Post coating had a minimal quantitative effect on the results and stabilized the plates for 214 days. We therefore recommend the incorporation of post coating.

Serological diagnosis of avian influenza in poultry: is the haemagglutination inhibition test really the 'gold standard'?

Background  The serological diagnosis of avian influenza (AI) can be performed using different methods, yet the haemagglutination inhibition (HI) test is considered the ‘gold standard’ for AI antibody subtyping. Although alternative diagnostic assays have been developed, in most cases, their accuracy has been evaluated in comparison with HI test results, whose performance for poultry has not been properly evaluated.

Objective  The objective of this study was to estimate the diagnostic sensitivity (Se) and specificity (Sp) of the HI test and six other diagnostic assays for the detection of AI antibodies without assuming a gold standard.

Methods  We applied a Bayesian version of latent class analysis to compare the results of multiple tests from different study settings reported in the literature.

Results  The results showed that the HI test has nearly perfect accuracy (i.e. 98·8% sensitivity and 99·5% specificity). It performed well in both chickens and turkeys and yet was less accurate in experimentally infected poultry, compared to naturally infected. Blocking ELISA and the indirect immunofluorescence assay also performed very well.

Conclusions  Given its very high Se and Sp, the HI test may be effectively considered a gold standard. In the framework of LPAI surveillance, where large numbers of samples have to be processed, the blocking ELISA could be a valid alternative to the HI test, in that it is almost as sensitive and specific as the HI test yet quicker and easier to automate.

Inter- and intraspecies transmission of canine influenza virus (H3N2) in dogs, cats, and ferrets

Background  The emergence of zoonotic viruses in domestic animals is a significant public health concern. Canine influenza virus (CIV) H3N2 is a virus that can infect companion animals and is, therefore, a potential public health concern.

Objective  This study investigated the inter‐ and intraspecies transmission of CIV among dogs, cats, and ferrets, under laboratory conditions, to determine whether transmission of the virus was possible between as well as within these domestic animal species.

Method  The transmission routes for inter‐ and intraspecies transmission were airborne and direct contact, respectively. Transmission was conducted through intranasal infection of dogs followed by exposure to either cats or ferrets and by comingling infected and naïve animals of the same species.

Results  The interspecies transmission of CIV H3N2 via airborne was only observed from dogs to cats and not from dogs to ferrets. However, direct intranasal infection of either cats or ferrets with CIV could induce influenza‐like clinical signs, viral shedding, and serological responses. Additionally, naïve cats and ferrets could be infected by CIV via direct contact with infected animals of the same species.

Conclusion  Cats appear to be another susceptible host of CIV H3N2, whereas ferrets are not likely natural hosts. The molecular‐based mechanism of interspecies and intraspecies transmission of CIV H3N2 should be further studied.

Generation and diagnostic application of monoclonal antibodies against Seneca Valley virus

Seneca Valley virus (SVV), a member of the Picornaviridae family, was implicated in a suspicious vesicular disease discovered in pigs from Canada in 2007. Because any outbreak of vesicular disease in pigs is assumed to be foot-and-mouth disease (FMD) until confirmed otherwise, a test for diagnosing the presence of SVV would be a very useful tool. To develop the diagnostic tests for SVV infection, 5 monoclonal antibodies (mAbs) were produced from mice immunized with binary ethylenimine (BEI)-inactivated SVV. Using a dot blot assay, the reactivity of the mAbs was confirmed to be specific for SVV, not reacting with any of the other vesicular disease viruses tested. The mAbs demonstrated reactivity with SVV antigen in infected cells by an immunohistochemistry assay. An SVV-specific competitive enzyme-linked immunosorbent assay (cELISA) was developed using BEI-inactivated SVV antigen and a mAb for serodiagnosis. The cELISA results were compared to the indirect isotype (immunoglobulin [Ig]M and IgG) ELISA and the virus neutralization test. All SVV experimentally inoculated pigs exhibited a positive SVV-specific antibody response at 6 days postinoculation, and the sera remained positive until the end of the experiment on day 57 (>40% inhibition) using the cELISA. The cELISA reflected the profile of the indirect ELISA for both IgM and IgG. This panel of SVV-specific mAbs is valuable for the identification of SVV antigen and the serological detection of SVV-specific antibodies.

Interspecies transmission of the canine influenza H3N2 virus to domestic cats in South Korea, 2010

In the past 4 years, incidences of endemic or epidemic respiratory diseases associated with canine influenza H3N2 virus in Asian dogs have been reported in countries such as South Korea and China. Canine species were considered to be the new natural hosts for this virus. However, at the beginning of 2010, influenza-like respiratory signs, such as dyspnoea, were also observed among cats as well as in dogs in an animal shelter located in Seoul, South Korea. The affected cats showed 100 % morbidity and 40 % mortality. We were able to isolate a virus from a lung specimen of a dead cat, which had suffered from the respiratory disease, in embryonated-chicken eggs. The eight viral genes isolated were almost identical to those of the canine influenza H3N2 virus, suggesting interspecies transmission of canine influenza H3N2 virus to the cat. Moreover, three domestic cats infected with intranasal canine/Korea/GCVP01/07 (H3N2) all showed elevated rectal temperatures, nasal virus shedding and severe pulmonary lesions, such as suppurative bronchopneumonia. Our study shows, for the first time, that cats are susceptible to canine influenza H3N2 infection, suggesting that cats may play an intermediate host role in transmitting the H3N2 virus among feline and canine species, which could lead to the endemic establishment of the virus in companion animals. Such a scenario raises a public health concern, as the possibility of the emergence of new recombinant feline or canine influenza viruses in companion animals with the potential to act as a zoonotic infection cannot be excluded.

Broad spectrum reactivity versus subtype specificity-trade-offs in serodiagnosis of influenza A virus infections by competitive ELISA

Avian influenza viruses (AIVs) of the H5 and H7 subtypes can cause substantial economic losses in the poultry industry and are a potential threat to public health. Serosurveillance of poultry populations is an important monitoring tool and can also be used for control of vaccination campaigns. The purpose of this study was to develop broadly reactive, yet subtype-specific competitive ELISAs (cELISAs) for the specific detection of antibodies to the notifiable AIV subtypes H5 and H7 as an alternative to the gold standard haemagglutination inhibition assay (HI). Broadly reacting monoclonal competitor antibodies (mAbs) and genetically engineered subtype H5 or H7 haemagglutinin antigen, expressed and in vivo biotinylated in insect cells, were used to develop the cELISAs. Sera from galliform species and water fowl (n=793) were used to evaluate the performance characteristics of the cELISAs. For the H5 specific cELISA, 98.1% test sensitivity and 91.5% test specificity (97.7% and 90.2% for galliforms; 98.9% and 92.6% for waterfowl), and for the H7 cELISA 97.3% sensitivity and 91.8% specificity (95.3% and 98.9% for galliforms; 100% and 82.7% for waterfowl) were reached when compared to HI. The use of competitor mAbs with broad spectrum reactivity within an AIV haemagglutinin subtype allowed for homogenous detection with high sensitivity of subtype-specific antibodies induced by antigenically widely distinct isolates including antigenic drift variants. However, a trade-off regarding sensitivity versus nonspecific detection of interfering antibodies induced by phylo- and antigenically closely related subtypes, e.g., H5 versus H2 and H7 versus H15, must be considered. The observed intersubtype antibody cross-reactivity remains a disturbance variable in AIV subtype-specific serodiagnosis which negatively affects specificity.