Recombinant Nucleocapsid Protein Research Articles

Development of a rapid immunochromatographic assay for detection of antibodies against porcine epidemic diarrhea virus.

An immunochromatographic test strip was developed for the detection of antibodies against porcine epidemic diarrhea virus (PEDV) in porcine serum. In this test, the recombinant nucleocapsid protein of PEDV was expressed in soluble form and purified by using Ni-NTA resin and gel filtration chromatography. The purified recombinant N protein conjugated with colloidal gold was dispensed on a conjugate pad as the detector. Staphylococcal protein A and rabbit anti-N protein IgG were blotted on a nitrocellulose membrane for the test and control lines, respectively. The immunochromatographic test strip specifically detected PEDV antibodies within 10 min and had higher sensitivity (96.0%) and specificity (90.8%) than those of commercial enzyme-linked immunosorbent assay (ELISA) kits. Our newly developed strip has great potential for the early diagnosis of PEDV infection.

Development of Recombinant Nucleocapsid Protein-based Enzyme-linked Immunosorbent Assay for Serological Detection of Winter Dysentery Disease

Winter Dysentery Disease is an acute and contagious viral disease that adversely affects dairy cattle on farms in Thailand. An indirect enzyme-linked immunosorbent assay (ELISA) based on the recombinant nucleocapsid (rN) protein which has been developed for antibodies detection against Winter Dysentery Disease was produced by an Escherichia coli protein expression system. The epitope antigen N protein was designed using almost total N gene fragments (8-430 aa, N gene). It was identified to be approximately 48 kDa as the rN protein and can bind bovine coronavirus dairy cattle positive serum by western blot analysis. The conditions of the ELISA method were optimized. The rN protein was standardized with a coating antigen concentration of 5 μg/well. The rN protein was tested with sera in both infected and uninfected dairy cattle. The dilution of the primary antibodies was identified as 1:50 using a checkerboard titration. The intra- and inter-assays were repeatable. The cut-off of the corrected OD450 value from mean ± 2SD (standard deviations) was established at 0.049. The percentage of specificity, sensitivity and accuracy between the developed rNELISA and a SVANOVIR® BCV-Ab ELISA kit was 96.3, 84.8 and 86.1%, respectively. Cohen’s kappa value of the developed ELISA compared with the commercial test kit was 0.71. The correlation coefficient of absorbance values from these two tests was 0.68. The recombinant nucleocapsid protein ELISA method might be helpful for bovine coronavirus diagnosis and surveillance.

Inclusion of MERS-spike protein ELISA in algorithm to determine serologic evidence of MERS-CoV infection.

The Centers for Disease Control and Prevention (CDC) algorithm for detecting presence of serum antibodies against Middle East Respiratory Syndrome coronavirus (MERS‐CoV) in subjects with potential infections with the virus has included screening by indirect ELISA against recombinant nucleocapsid (N) protein and confirmation by immunofluorescent staining of infected monolayers and/or microneutralization titration. Other international groups include indirect ELISA assays using the spike (S) protein, as part of their serological determinations. In the current study, we describe development and validation of an indirect MERS‐CoV S ELISA to be used as part of our serological determination for evidence of previous exposure to the virus.

Human Puumala hantavirus infection in northern Sweden; increased seroprevalence and association to risk and health factors

BackgroundThe rodent borne Puumala hantavirus (PUUV) causes haemorrhagic fever with renal syndrome in central and northern Europe. The number of cases has increased and northern Sweden has experienced large outbreaks in 1998 and 2006–2007 which raised questions regarding the level of immunity in the human population.MethodsA randomly selected population aged between 25 and 74 years from northern Sweden were invited during 2009 to participate in a WHO project for monitoring of trends and determinants in cardiovascular disease. Health and risk factors were evaluated and sera from 1,600 participants were available for analysis for specific PUUV IgG antibodies using a recombinant PUUV nucleocapsid protein ELISA.ResultsThe overall seroprevalence in the investigated population was 13.4 %, which is a 50 % increase compared to a similar study only two decades previously. The prevalence of PUUV IgG increased with age, and among 65–75 years it was 22 %. More men (15.3 %) than women (11.4 %) were seropositive (p < 0.05). The identified risk factors were smoking (OR = 1.67), living in rural areas (OR = 1.92), and owning farmland or forest (OR = 2.44). No associations were found between previous PUUV exposure and chronic lung disease, diabetes, hypertension, renal dysfunction, stroke or myocardial infarction.ConclusionsPUUV is a common infection in northern Sweden and there is a high life time risk to acquire PUUV infection in endemic areas. Certain risk factors as living in rural areas and smoking were identified. Groups with increased risk should be targeted for future vaccination when available, and should also be informed about appropriate protection from rodent secreta.Electronic supplementary materialThe online version of this article (doi:10.1186/s12879-016-1879-2) contains supplementary material, which is available to authorized users.

Development of Recombinant Nucleocapsid Protein based indirect ELISA for Serodiagnosis of Peste des Petits Ruminants in Sheep and Goats

Development of Recombinant Nucleocapsid Protein based indirect ELISA for Serodiagnosis of Peste des Petits Ruminants in Sheep and Goats

Genetic and antigenic characterization of recombinant nucleocapsid proteins derived from canine coronavirus and canine respiratory coronavirus in China.

To characterize the antigenicity of nucleocapsid proteins (NP) derived from canine coronavirus (CCoV) and canine respiratory coronavirus (CRCoV) in China, the N genes of CCoV (CCoV-BJ70) and CRCoV (CRCoV-BJ202) were cloned from swabs obtained from diseased pet dogs in Beijing and then sequenced. The recombinant NPs (rNPs) were expressed in Escherichia coli and purified by nickel-affinity column and size exclusion chromatography. Sequencing data indicated that the N genes of CCoV-BJ70 and CRCoV-BJ202 belonging to two distinctly different groups were relatively conserved within each subgroup. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) results showed that rNPs of CCoV and CRCoV were expressed efficiently and isolated with a final purity of over 95%. Western blot analysis revealed the rNP from CRCoV could cross-react with mice antisera against human coronavirus (HCoV-229E, NL63, OC43, HKU1), while rNP of CCoV had cross-reactivity with only anti-sera against viruses belonging to the same group (HCoV-229E and NL63). In summary, CCoV and CRCoV rNPs were successfully expressed in E. coli and showed antigenic cross-reactivity with antisera raised against human coronaviruses. These findings indicate that further serologic studies on coronavirus infections at the animal-human interface are needed.

Establishment of serological test to detect antibody against ferret coronavirus.

Since there is no available serological methods to detect antibodies to ferret coronavirus (FRCoV), an enzyme-linked immunosorbent assay (ELISA) using recombinant partial nucleocapsid (N) proteins of the ferret coronavirus (FRCoV) Yamaguchi-1 strain was developed to establish a serological method for detection of FRCoV infection. Many serum samples collected from ferrets recognized both a.a. 1–179 and a.a. 180–374 of the N protein, but two serum samples did not a.a. 180–374 of the N protein. This different reactivity was also confirmed by immunoblot analysis using the serum from the ferret.Therefore, the a.a. 1–179 of the N protein was used as an ELISA antigen. Serological test was carried out using sera or plasma of ferrets in Japan. Surprisingly, 89% ferrets in Japan had been infected with FRCoV. These results indicated that our established ELISA using a.a. 1–179 of the N protein is useful for detection of antibody to FRCoV for diagnosis and seroepidemiology of FRCoV infection.

Serological Survey of Hantavirus in Inhabitants from Tropical and Subtropical Areas of Brazil

Brazil has reported more than 1,600 cases of hantavirus cardiopulmonary syndrome (HPS) since 1993, with a 39% rate of reported fatalities. Using a recombinant nucleocapsid protein of Araraquara virus, we performed ELISA to detect IgG antibodies against hantavirus in human sera. The aim of this study was to analyze hantavirus antibody levels in inhabitants from a tropical area (Amazon region) in Rondônia state and a subtropical (Atlantic Rain Forest) region in São Paulo state, Brazil. A total of 1,310 serum samples were obtained between 2003 and 2008 and tested by IgG-ELISA, and 82 samples (6.2%), of which 62 were from the tropical area (5.8%) and 20 from the subtropical area (8.3%), tested positive. Higher levels of hantavirus antibody were observed in inhabitants of the populous subtropical areas compared with those from the tropical areas in Brazil.

A recombinant nucleocapsid protein-based indirect enzyme-linked immunosorbent assay to detect antibodies against porcine deltacoronavirus.

Recently, porcine deltacoronavirus (PDCoV) has been proven to be associated with enteric disease in piglets. Diagnostic tools for serological surveys of PDCoV remain in the developmental stage when compared with those for other porcine coronaviruses. In our study, an indirect enzyme-linked immunosorbent assay (ELISA) (rPDCoV-N-ELISA) was developed to detect antibodies against PDCoV using a histidine-tagged recombinant nucleocapsid (N) protein as an antigen. The rPDCoV-N-ELISA did not cross-react with antisera against porcine epidemic diarrhea virus, swine transmissible gastroenteritis virus, porcine group A rotavirus, classical swine fever virus, porcine circovirus-2, porcine pseudorabies virus, and porcine reproductive and respiratory syndrome virus; the receiver operating characteristic (ROC) curve analysis revealed 100% sensitivity and 90.4% specificity of the rPDCoV-N-ELISA based on samples of known status (n=62). Analyses of field samples (n=319) using the rPDCoV-N-ELISA indicated that 11.59% of samples were positive for antibodies against PDCoV. These data demonstrated that the rPDCoV-N-ELISA can be used for epidemiological investigations of PDCoV and that PDCoV had a low serum prevalence in pig population in Heilongjiang province, northeast China.

Saliva as an alternative specimen for detection of Schmallenberg virus-specific antibodies in bovines

BackgroundSchmallenberg virus (SBV), discovered in continental Europe in late 2011, causes mild clinical signs in adult ruminants, including diarrhoea and reduced milk yield. However, fetal infection can lead to severe malformation in newborn offspring. Enzyme-linked immunosorbent assays (ELISA) are commercially available for detection of SBV-specific antibodies in bovine sera and milk. Here we describe the development and evaluation of an indirect ELISA based on a yeast derived recombinant SBV nucleocapsid protein (N) for the detection of SBV-specific antibodies in bovine saliva. Development of a non-invasive test to detect antibodies in individual bovine saliva samples could potentially provide a test suitable for calves and adult cattle. The aim of this study was to investigate the agreement between the levels of antibodies (IgG) measured in milk and sera, and the level of antibodies (IgG and IgA) in saliva, in comparison with the antibody levels detected in sera and milk with commercially available test.ResultsSerum, milk and saliva samples from 58 cows were collected from three dairy herds in Lithuania and tested for the presence of SBV-specific antibodies. The presence of IgG antibodies was tested in parallel serum and milk samples, while the presence of IgA and IgG antibodies was tested in saliva samples. The presence of SBV-specific IgG and IgA in saliva was tested using an indirect ELISA based on a yeast-derived recombinant N protein. The presence of SBV-specific IgG in milk and sera was tested in parallel using a commercial recombinant protein based test. The sensitivities of the newly developed tests were as follows: 96 % for the IgG serum assay and 94 % for the IgG milk assay and 85 % and 98 % for IgG and IgA in saliva tests, when compared with data generated by a commercial IgG assay.ConclusionsData from testing the saliva IgG and IgA and also the milk and serum IgG with indirect SBV-specific ELISAs showed close agreement with the commercial serum and milk IgG assay data. The level of IgG in saliva was notably lower in comparison to IgA. The newly developed method exhibits the potential to serve as an easily transferable tool for epidemiological studies.Electronic supplementary materialThe online version of this article (doi:10.1186/s12917-015-0552-0) contains supplementary material, which is available to authorized users.

Development and Evaluation of Recombinant Nucleocapsid Protein Based Diagnostic ELISA for Detection of Nipah Virus Infection in Pigs

The recombinant viral protein-based indirect enzyme-linked immunosorbent assay (ELISA) is a cost-effective, safe, specific, and rapid tool to diagnose the viral infection. Nipah virus nucleocapsid (NiV-N) protein was expressed in Escherichia coli and purified by histidine tag-based affinity chromatography. The N protein was selected based on its immuno dominance and conservation among different NiV strains. An indirect immunoglobulin G (IgG) enzyme-linked immunosorbent assay (ELISA) for swine sera was optimized using the recombinant NiV-N protein as an antigen along with negative and positive controls. The background reading was blocked using skim milk powder and chicken serum. A total number of 1709 swine serum samples from various states of India were tested with indirect ELISA and Western blot. The test was considered positive only when its total reactivity reading was higher than 0.2 cut-off value and the ratio of the total reactivity to the background reading was more than 2.0. Since specificity is high for Western blotting it was used as standard test for comparison of results of indirect ELISA. Sensitivity and specificity of indirect ELISA was 100% and 98.7%, respectively, in comparison with Western blotting. Recombinant N protein-based ELISA can be used in screening large number of serum samples for epidemiological investigations in developing countries where high containment laboratories are not available to handle this zoonotic virus.

Structural characterization by transmission electron microscopy and immunoreactivity of recombinant Hendra virus nucleocapsid protein expressed and purified from Escherichia coli

Hendra virus (family Paramyxoviridae) is a negative sense single-stranded RNA virus (NSRV) which has been found to cause disease in humans, horses, and experimentally in other animals, e.g. pigs and cats. Pteropid bats commonly known as flying foxes have been identified as the natural host reservoir. The Hendra virus nucleocapsid protein (HeV N) represents the most abundant viral protein produced by the host cell, and is highly immunogenic with naturally infected humans and horses producing specific antibodies towards this protein.The purpose of this study was to express and purify soluble, functionally active recombinant HeV N, suitable for use as an immunodiagnostic reagent to detect antibodies against HeV. We expressed both full-length HeV N, (HeV NFL), and a C-terminal truncated form, (HeV NCORE), using a bacterial heterologous expression system. Both HeV N constructs were engineered with an N-terminal Hisx6 tag, and purified using a combination of immobilized metal affinity chromatography (IMAC) and size exclusion chromatography (SEC). Purified recombinant HeV N proteins self-assembled into soluble higher order oligomers as determined by SEC and negative-stain transmission electron microscopy. Both HeV N proteins were highly immuno-reactive with sera from animals and humans infected with either HeV or the closely related Nipah virus (NiV), but displayed no immuno-reactivity towards sera from animals infected with a non-pathogenic paramyxovirus (CedPV), or animals receiving Equivac® (HeV G glycoprotein subunit vaccine), using a Luminex-based multiplexed microsphere assay.

Serological survey of Seewis virus antibodies in patients suspected for hantavirus infection in Finland; a cross-reaction between Puumala virus antiserum with Seewis virus N protein?

Puumala virus (PUUV, carried by Myodes glareolus) co-circulates with Seewis virus (SWSV, carried by Sorex araneus) in Finland. While PUUV causes 1000-3000 nephropathia epidemica (NE) cases annually, the pathogenicity of SWSV to man is unknown. To study the prevalence of SWSV antibodies in hantavirus fever-like patients' sera, we used recombinant SWSV nucleocapsid (N) protein as the antigen in ELISA, immunofluorescence assay (IFA) and immunoblotting. While characterizing the recombinant SWSV N protein, we observed that a polyclonal rabbit antiserum against PUUV N protein cross-reacted with SWSV N protein and vice versa. We initially screened 486 (450 PUUV-seronegative and 36 PUUV-seropositive) samples sent to Helsinki University Hospital Laboratory for PUUV serodiagnosis during 2002 and 2007 in an SWSV N protein IgG ELISA. In total, 4.2 % (19/450) of the PUUV-seronegative samples were reactive in the SWSV N protein IgG ELISA and none of the tested samples [43 PUUV-seronegative (weakly reactive in the SWSV IgG ELISA) and 15 random] were reactive in the SWSV N protein IgM ELISA. None of the IgG reactions could be confirmed by IFA or immunoblotting. Furthermore, among the 36 PUUV-seropositive samples three were reactive in SWSV N protein IgG and ten in SWSV N protein IgM ELISA. One PUUV-seropositive sample reacted with SWSV N protein in IFA and four in immunoblotting. Finally, we applied competitive ELISA to confirm that the observed reactivity was due to cross-reactivity rather than a true SWSV response. In conclusion, no evidence of SWSV infection was found among the 486 samples studied; however, we did demonstrate that PUUV antiserum cross-reacted with shrew-borne hantavirus N protein.

Development and evaluation of two truncated recombinant NP antigen-based indirect ELISAs for detection of bovine parainfluenza virus type 3 antibodies in cattle

Bovine parainfluenza virus type 3 (BPIV3) is one of the most important viral respiratory pathogens in both young and adult cattle. Nucleocapsid protein (NP) is the most abundant viral protein and the main regulator of virus replication and transcription. In this study, amino acid sequence data of BPIV3 NP was used to identify potential linear epitopic regions, which were subsequently used to design truncated recombinant NP antigens. The amino-terminal region (aa 9-157, NP-N) and the carboxy-terminal region (aa 391-500, NP-C) were selected, and these two truncated recombinant BPIV3 NP proteins were expressed in Escherichia coli based on the results of prediction studies. Furthermore, Enzyme-Linked Immunosorbent Assays (ELISAs) were established using the truncated recombinant BPIV3-N proteins as antigens, and 154 clinical samples were used to evaluate the newly established ELISA systems in comparison with a virus neutralisation test (VNT) as a reference. The results showed that a high coincidence rate was observed for the data that were obtained by the two methods. The sensitivity of NP-N ELISA and NP-C ELISA were 98.4% and 94.6%, respectively, and the specificity of both ELISAs was 100% with reference to the VNTs. Our data indicated that both ends of NP have high immunogenicity during BPIV3 infection and that they were good targets for serodiagnosis. The ELISAs based on the two truncated proteins were especially suitable for use in large-scale epidemiological investigations.

Identification of three antigen epitopes on the nucleocapsid protein of the genotype C of bovine parainfluenza virus type 3

Bovine parainfluenza virus type 3 (BPIV3) is an important respiratory tract pathogen for both young and adult cattle. So far, three genotypes A, B and C of BPIV3 have been described on the basis of genetic and phylogenetic analysis. But fine mapping of epitopes of BPIV3 is scant and the antigenic variations among the three genotypes of BPIV3 have not been reported. Nucleocapsid protein (NP) is the most abundant protein in the virion and highly conserved in BPIV3, which is crucial for the induction of protective immunity in host. To identify antigenic determinants of BPIV3 NP, a panel of monoclonal antibodies (mAbs) was tested against a series of overlapping recombinant NP fragments expressed in Escherichia coli. Firstly, six monoclonal antibodies (mAbs) against NP of the genotype C of BPIV3 (BPIV3c) were generated by using the purified BPIV3c strain SD0835 as immunogen and the recombinant NP of SD0835 as screening antigen. Then three antigen epitopes were identified with the six mAbs. One epitope 91GNNADVKYVIYM102 was recognized by mAb 5E5. The mAbs 7G5, 7G8, 7G9, and 7H5 were reactive with another epitope 407FYKPTGG413. The third epitope 428ESRGDQDQ435 was reactive with mAb 6F8. Further analysis showed that the epitope (91–102 amino acids [aa]) was the most conserved and reactive with mAb 5E5 for all three genotypes of BPIV3 and HPIV3. The epitope (407–413 aa) was relatively conserved and reactive with mAbs 7G5, 7G8, 7G9, and 7H5 for BPIV3a, BPIV3c and HPIV3, but not reactive with BPIV3b. The epitope (428–435 aa) was less conserved and was reactive only with mAb 6F8 for BPIV3a and BPIV3c. These results suggested that there were evident antigenic variations among the three genotypes of BPIV3 and HPIV3. The mAb 6F8 could be used to detect BPIV3a and BPIV3c. The mAbs 7G5, 7G8, 7G9, and 7H5 might be used for differentiate BPIV3a, BPIV3c and HPIV3 from BPIV3b. The mAb 5E5 might be used for detecting all three types of BPIV3 and HPIV3. The results in this study would have potential applications in the development of suitable diagnostic techniques for BPIV3, which was prevalent in China.

Antigenic relationships among porcine epidemic diarrhea virus and transmissible gastroenteritis virus strains.

Porcine epidemic diarrhea virus (PEDV) and transmissible gastroenteritis virus (TGEV) are economically important swine enteropathogenic coronaviruses. These two viruses belong to two distinct species of the Alphacoronavirus genus within Coronaviridae and induce similar clinical signs and pathological lesions in newborn piglets, but they are presumed to be antigenically distinct. In the present study, two-way antigenic cross-reactivity examinations between the prototype PEDV CV777 strain, three distinct U.S. PEDV strains (the original highly virulent PC22A, S indel Iowa106, and S 197del PC177), and two representative U.S. TGEV strains (Miller and Purdue) were conducted by cell culture immunofluorescent (CCIF) and viral neutralization (VN) assays. None of the pig TGEV antisera neutralized PEDV and vice versa. One-way cross-reactions were observed by CCIF between TGEV Miller hyperimmune pig antisera and all PEDV strains. Enzyme-linked immunosorbent assays, immunoblotting using monoclonal antibodies and Escherichia coli-expressed recombinant PEDV and TGEV nucleocapsid (N) proteins, and sequence analysis suggested at least one epitope on the N-terminal region of PEDV/TGEV N protein that contributed to this cross-reactivity. Biologically, PEDV strain CV777 induced greater cell fusion in Vero cells than did U.S. PEDV strains. Consistent with the reported genetic differences, the results of CCIF and VN assays also revealed higher antigenic variation between PEDV CV777 and U.S. strains. Evidence of antigenic cross-reactivity between porcine enteric coronaviruses, PEDV and TGEV, in CCIF assays supports the idea that these two species are evolutionarily related, but they are distinct species defined by VN assays. Identification of PEDV- or TGEV-specific antigenic regions allows the development of more specific immunoassays for each virus. Antigenic and biologic variations between the prototype and current PEDV strains could explain, at least partially, the recurrence of PEDV epidemics. Information on the conserved antigenicity among PEDV strains is important for the development of PEDV vaccines to protect swine from current highly virulent PEDV infections.

Serological diagnosis of feline coronavirus infection by immunochromatographic test.

The immunochromatographic assay (ICA) is a simple antibody–antigen detection method, the results of which can be rapidly obtained at a low cost. We designed an ICA to detect anti-feline coronavirus (FCoV) antibodies. A colloidal gold-labeled recombinant FCoV nucleocapsid protein (rNP) is used as a conjugate. The Protein A and affinity-purified cat anti-FCoV IgG are blotted on the test line and the control line, respectively, of the nitrocellulose membrane. The specific detection of anti-FCoV antibodies was possible in all heparin-anticoagulated plasma, serum, whole blood, and ascitic fluid samples from anti-FCoV antibody positive cats, and nonspecific reaction was not noted in samples from anti-FCoV antibody negative cats.

A Glycoprotein Subunit Vaccine Elicits a Strong Rift Valley Fever Virus Neutralizing Antibody Response in Sheep

Rift Valley fever virus (RVFV), a member of the Bunyaviridae family, is a mosquito-borne zoonotic pathogen that causes serious morbidity and mortality in livestock and humans. The recent spread of the virus beyond its traditional endemic boundaries in Africa to the Arabian Peninsula coupled with the presence of susceptible vectors in nonendemic countries has created increased interest in RVF vaccines. Subunit vaccines composed of specific virus proteins expressed in eukaryotic or prokaryotic expression systems are shown to elicit neutralizing antibodies in susceptible hosts. RVFV structural proteins, amino-terminus glycoprotein (Gn), and carboxyl-terminus glycoprotein (Gc), were expressed using a recombinant baculovirus expression system. The recombinant proteins were reconstituted as a GnGc subunit vaccine formulation and evaluated for immunogenicity in a target species, sheep. Six sheep were each immunized with a primary dose of 50 μg of each vaccine immunogen with the adjuvant montanide ISA25; at day 21, postvaccination, each animal received a second dose of the same vaccine. The vaccine induced a strong antibody response in all animals as determined by indirect enzyme-linked immunosorbent assay (ELISA). A plaque reduction neutralization test (PRNT80) showed the primary dose of the vaccine was sufficient to elicit potentially protective virus neutralizing antibody titers ranging from 40 to 160, and the second vaccine dose boosted the titer to more than 1280. Furthermore, all animals tested positive for neutralizing antibodies at day 328 postvaccination. ELISA analysis using the recombinant nucleocapsid protein as a negative marker antigen indicated that the vaccine candidate is DIVA (differentiating infected from vaccinated animals) compatible and represents a promising vaccine platform for RVFV infection in susceptible species.

다양한 PRRSV 감염상태에 있는 돼지 혈청을 이용한 PRRS 항체 ELISA 키트들의 비교 평가

Porcine reproductive and respiratory syndrome virus (PRRSV) causes major economic losses to the Korean pig industry. ELISA tests using recombinant nucleocapsid protein of PRRSV have been most commonly used for PRRS diagnostics. In the current study, two commercial PRRSV ELISA kits (Bionote PRRSV Antibody ELISA and IDEXX 3XR PRRS Antibody ELISA) have been compared using sera collected from 19 swine farms in various stages of PRRSV infection confirmed by professional diagnostic centers. Thus 130 sera collected from 5 different farms with active PRRSV infection, 130 sera from 6 different farms with PRRS-stabilized status, and 140 sera from 8 different farms with PRRS-free status were evaluated to determine the correlation of test results between those ELISA kits. Both ELISA kits showed a good correlation [PRRSV-positive farms (<TEX>$R^2$</TEX>=0.6375) and stabilized farms (<TEX>$R^2$</TEX>=0.8928)] in sample-to-positive (S/P) ratio va lues. Among the 140 sera from negative farms, one sample was falsely positive by either of the ELISA kits. In conclusion, both of the ELISA kits showed a good correlation when applied on field samples collected from farms at various stages of PRRSV infection. Bionote ELISA or IDEXX ELISA gave a false positive result on 1 out of 140 negative samples so their specificity was calculated as 99.3%. Therefore, Bionote ELISA would be a good complementary and alternative method for IDEXX ELISA kit, and vice versa.

Recombinant nucleocapsid protein based single serum dilution ELISA for the detection of antibodies to infectious bronchitis virus in poultry

Avian infectious bronchitis is ubiquitous and highly contagious disease of poultry, with profound effect on commercial poultry production. For effective control of infectious bronchitis virus (IBV), quick and specific diagnosis is of utmost importance. In this study, the virus was isolated from clinical samples from India and the full length nucleocapsid (N) gene was amplified, cloned and expressed in a prokaryotic system. The purified recombinant N protein based single serum dilution enzyme linked immunosorbent assay (ELISA) was developed for IBV to measure specific antibody in the sera of chickens. A total of 310 chicken sera samples were tested using the commercial IDEXX kit along with the assay developed. A linear correlation was obtained between predicted antibody titres at a single working dilution of 1:100 and the corresponding serum titres observed as determined by the standard serial dilution method. Regression analysis was used to construct a standard curve from which an equation was derived which confirmed their correlation. The developed equation was then used to extrapolate predicated ELISA antibody titer from corrected absorbance readings of the single working dilution. The assay proved to be specific (95.8%) and sensitive (96.8%) when compared to the commercial IDEXX ELISA test.