Comparative studies with an enzyme-linked immunosorbent assay (ELISA) for antibodies to avian infectious bronchitis virus

Infectious Bronchitis Virus (Gammacoronavirus) in Poultry Farming: Vaccination, Immune Response and Measures for Mitigation

Infectious bronchitis virus (IBV) poses significant financial and biosecurity challenges to the commercial poultry farming industry. IBV is the causative agent of multi-systemic infection in the respiratory, reproductive and renal systems, which is similar to the symptoms of various viral and bacterial diseases reported in chickens. The avian immune system manifests the ability to respond to subsequent exposure with an antigen by stimulating mucosal, humoral and cell-mediated immunity. However, the immune response against IBV presents a dilemma due to the similarities between the different serotypes that infect poultry. Currently, the live attenuated and killed vaccines are applied for the control of IBV infection; however, the continual emergence of IB variants with rapidly evolving genetic variants increases the risk of outbreaks in intensive poultry farms. This review aims to focus on IBV challenge-infection, route and delivery of vaccines and vaccine-induced immune responses to IBV. Various commercial vaccines currently have been developed against IBV protection for accurate evaluation depending on the local situation. This review also highlights and updates the limitations in controlling IBV infection in poultry with issues pertaining to antiviral therapy and good biosecurity practices, which may aid in establishing good biorisk management protocols for its control and which will, in turn, result in a reduction in economic losses attributed to IBV infection.

Immunoprofiling of peripheral blood from infectious bronchitis virus vaccinated MHC-B chicken lines - Monocyte MHC-II expression as a potential correlate of protection

Vaccination programs are implemented in poultry farms to limit outbreaks and spread of infectious bronchitis virus (IBV), which is a substantial economic burden in the poultry industry. Immune correlates, used to predict vaccine efficacy, have proved difficult to find for IBV-vaccine-induced protection. To find correlates of IBV-vaccine-induced protection, hence, we employed a flow cytometric assay to quantify peripheral leucocyte subsets and expression of cell surface markers of six different non-vaccinated and vaccinated Major Histocompatibility Complex (MHC) haplotypes. Non-vaccinated and vaccinated MHC haplotypes presented differential leucocyte composition and IBV viral load. A strong effect of MHC-B, but not vaccination, on several leucocyte subsets resulted in positive correlations with IBV viral load based on MHC haplotype ranking. In addition, a strong effect of MHC-B and vaccination on monocyte MHC-II expression showed that animals with highest monocyte MHC-II expression had weakest vaccine-induced protection. In conclusion, we found several interesting MHC-B related immune correlates of protection and that flow cytometric analysis can be employed to study correlates of IBV-vaccine-induced protection.

Immune Responses to Virulent and Vaccine Strains of Infectious Bronchitis Viruses in Chickens

Infectious bronchitis (IB) is an acute and highly contagious chicken viral disease, causing severe economic losses to poultry producers worldwide. In the last few decades, infectious bronchitis virus (IBV) has been extensively studied, but knowledge of immune responses to virulent or vaccine strains of IBVs remains limited. This review focuses on fundamental aspects of immune responses against IBV, including the role of pattern recognition receptors (PRRs) in identification of conserved viral structures and the role of different components of innate immunity (e.g., heterophils, macrophages, dendritic cells, acute phase protein, and cytokines). Studies on adaptive immune activation and the role of humoral and cellular immunity in IBV clearance are also reviewed. Multiple interlinking immune responses are essential for protection against virulent IBVs, including passive, innate, adaptive, and effector T cells active at mucosal surfaces. Although the development of approaches for chicken transcriptome and proteome analyses have greatly helped the understanding of the underlying genetic mechanisms for immunity, there are still major knowledge gaps, such as the role of mucosal and cellular responses to IBVs. In view of recent reports of emergent IBV variants in many countries, there is renewed interest in a more complete understanding of poultry immune responses to both virulent and vaccine strains of IBVs. This will be critical for developing new vaccine or vaccination strategies and other intervention programs.

Mucosal, Cellular, and Humoral Immune Responses Induced by Different Live Infectious Bronchitis Virus Vaccination Regimes and Protection Conferred against Infectious Bronchitis Virus Q1 Strain

The objectives of the present study were to assess the mucosal, cellular, and humoral immune responses induced by two different infectious bronchitis virus (IBV) vaccination regimes and their efficacy against challenge by a variant IBV Q1. One-day-old broiler chicks were vaccinated with live H120 alone (group I) or in combination with CR88 (group II). The two groups were again vaccinated with CR88 at 14 days of age (doa). One group was kept as the control (group III). A significant increase in lachrymal IgA levels was observed at 4 doa and then peaked at 14 doa in the vaccinated groups. The IgA levels in group II were significantly higher than those in group I from 14 doa. Using immunohistochemistry to examine changes in the number of CD4(+) and CD8(+) cells in the trachea, it was found that overall patterns of CD8(+) cells were dominant compared to those of CD4(+) cells in the two vaccinated groups. CD8(+) cells were significantly higher in group II than those in group I at 21 and 28 doa. All groups were challenged oculonasally with a virulent Q1 strain at 28 doa, and their protection was assessed. The two vaccinated groups gave excellent ciliary protection against Q1, although group II's histopathology lesion scores and viral RNA loads in the trachea and kidney showed greater levels of protection than those in group I. These results suggest that greater protection is achieved from the combined vaccination of H120 and CR88 of 1-day-old chicks, followed by CR88 at 14 doa.

Immune responses to structural proteins of avian infectious bronchitis virus

Chickens were vaccinated with live and inactivated infectious bronchitis virus (IBV), and antibody responses to the individual structural proteins, S1, S2, M and N, followed by ELISA and western blotting. All four structural proteins elicited an antibody response in chicks vaccinated with either live or inactivated IBV. The S1, S2 and N proteins elicited similar titres of antibodies following vaccination with live IBV, whereas the M glycoprotein elicited significantly lower titres. Time of appearance and the course of development of the S1, S2 and N ELISA antibodies were similar, being first detected 2 weeks after vaccination and coincided with appearance of virus neutralizing antibodies. The M antibodies were first detected 4 weeks after vaccination. S1, S2, and N antibody titres were significantly higher in chicks vaccinated at 14 days of age than in chicks vaccinated at either 1 or 7 days of age, and reached maximum levels 4 weeks after the second vaccination. The S1, S2 and N proteins induced cross-reactive antibodies, whereas the M glycoprotein induced antibodies of limited cross-reactivity. Titres of cross-reactive N antibodies were higher than titres of cross-reactive S1 and S2 antibodies, which were similar. Epitopes on the N and S2 proteins that gave rise to cross-reactive antibodies showed the same degree of conservation, whereas the cross-reactive S1 epitopes were marginally less conserved. Vaccination with inactivated virus induced significantly lower antibody titres and at least three vaccinations were necessary for induction of S1, S2, N and M antibodies in all chicks. The S2 glycoprotein was the most immunogenic structural protein following vaccination with inactivated virus. All four proteins induced cell-mediated immune responses in chicks vaccinated with live IBV as determined by a delayed type hypersensitivity response.

Maternally-derived antibody to infectious bronchitis virus: Its detection in chick trachea and serum and its role in protection

Chicks with maternally-derived IgG antibodies to infectious bronchitis virus (IBV) were protected against challenge with a mixture of IBV and Escherichia coli. This protective immunity lasted for at least 1 week. IBV-specific IgG was detected, using an ELISA, in the majority of tracheal washes taken from chicks aged 1 day and 1 week that had been hatched from IBV-infected hens. Some of the 2-week-old chicks also had detectable antibody. This tracheal IgG may be an important factor in mediating protective immunity. The origin and transport of the IgG into the trachea are discussed. IBV-specific IgG was detected in chick serum and had a half-life of 4.5 days. Yolk samples, collected from eggs laid by IBV-infected hens, were tested for the presence of viral-specific IgG antibodies. The sequential IgG antibody response to IBV in yolk was determined. Specific antibodies were detected at highest concentrations 16 to 18 days after infection and then declined. A second inoculation of an inactivated oil-based vaccine induced high concentrations of IBV-specific antibodies in the yolk which were maintained for the 60 days of the experiment. Detection of specific IgG in the yolk could be used as a means of assessing response to vaccination.

Comparison of the haemagglutination inhibition test and the serum neutralisation test in tracheal organ cultures for typing infectious bronchitis virus strains

Five strains of infectious bronchitis (IB) virus, which had been compared antigenically by the serum neutralisation (SN) test in tracheal organ cultures (OC), were arbitrarily coded and then compared by the haemagglutination inhibition (HI) test. Their antigenic relationships were found to be similar by the two methods but, because of the high and variable cross reactions found in the HI test, the differences between the strains were less clear by that method. It was concluded that the HI test, in its present state of development, is considerably less type-specific than the SN test in OC, and cannot be recommended for defining antigenic relationships between strains of IB virus. However, it retains its value for diagnosing IB or for monitoring the vaccinal status of flocks.

The detection of specific IgM to infectious bronchitis virus in chicken serum using an ELISA

An ELISA is reported for the detection of specific IgM to infectious bronchitis virus (IBV) in serum samples from IBV-infected chickens. Both IgM and IgG antibodies to a heterologous, as well as to a homologous, strain could be detected by the ELISA. The IgM response was both rapid and transient, suggesting that its detection could be used as a means of identifying a recent IBV infection. Because IgG appeared to compete successfully with IgM for sites on the viral antigen, it was found necessary to separate IgM from IgG prior to testing in the ELISA.

The isolation and characterisation of six avian infectious bronchitis viruses isolated in Morocco

The first isolation and characterisation of infectious bronchitis (IB) viruses from poultry flocks in Morocco are reported. Five isolates designated D, E, F, H and M were related serologically to the Massachusetts serotype, while the sixth, isolate G, was found to be different from any previously reported serotype of IB virus. Neutralising antibodies to isolate G have been detected in sera collected from commercial flocks in Britain, although the virus has not been isolated. While all six isolates caused respiratory disease typical of IB in experimentally infected 3-week-old specified pathogen-free (SPF) chickens, isolate G was unusual in that it could be isolated from several parts of the alimentary tract for up to 21 days post inoculation, and from the duodenum up to 28 days. H120 vaccines protected chicks challenged with isolates E and F but not isolate G.

Comparison of the enzyme-linked immunosorbent assay (ELISA), haemagglutination inhibition test and agar gel precipitation test for detection of antibodies to avian infectious bronchitis virus

The immune response after vaccination with infectious bronchitis virus (IBV) under field conditions was measured by the ELISA, haemagglutination-inhibition (HI) and agar-gel precipitin (AGP), tests. Vaccinations were performed in three flocks and one experimental group via the drinking water with the vaccine strains H 120 and H 52. In each flock 40 random serum samples were taken every 2 weeks and tested individually. In the experimental group blood samples were collected every week from each of the 10 chickens. The primary vaccination with H 120 resulted in a rapid increase of antibody titre as detected by ELISA followed by a slow decrease over the next few weeks. By the HI and AGP tests no antibody responses could be seen after this primary vaccination. Revaccination with the H 52 strain provoked a further increase in ELISA titres. In the experimental group, and in flock W, a similar increase occurred by the HI test and precipitating antibodies appeared. The formation of HI antibodies in flock T (nipple waterers) was somewhat retarded and precipitating antibodies were just detectable. In flock F revaccination did not result in the immediate production of HI and AGP antibodies. However, 6 weeks after revaccination a significant rise in ELISA, HI and AGP antibodies was observed, probably as the result of a field infection. It was demonstrated that, based on the higher sensitivity, the ELISA test is more suitable than HI and AGP to monitor antibody responses to vaccination against infectious bronchitis. Strain specificity in the HI test is discussed as a reason for its failure to detect antibodies after primary vaccination with the highly attenuated vaccine strain H 120.

Comparison of the enzyme linked immunosorbent assay, the haemagglutination inhibition test and the agar gel precipitation test for the detection of antibodies against infectious bronchitis and Newcastle disease in commercial broilers

Serological results as obtained by the agar gel precipitation (AGP) test, haemagglutination inhibition (HI) test (M41, D274, D1466) and an enzyme linked immunosorbent assay (ELISA) from commercial broiler flocks, which had suffered from a clinical infectious bronchitis (IB) infection in the fattening period, were compared with serological findings of control broiler flocks. In addition the Hi-test and ELISA for Newcastle disease (ND) were compared. The AGP results differ significantly between groups. The test had a low sensitivity. The results of the HI-IBV tests were similar for both groups and no difference was seen between flocks with or without clinical IB problems. The IBV ELISA showed a highly significant difference between the two groups. In contrast to the low and not significant correlation coefficients (r) between the IBV HI tests and the ELISA, the value of r between the NDV HI and ELISA was high. The results indicate an ELISA as the preferred test for the diagnosis of IB in broilers.

Coronavirus avian infectious bronchitis virus

Infectious bronchitis virus (IBV), the coronavirus of the chicken (Gallus gallus), is one of the foremost causes of economic loss within the poultry industry, affecting the performance of both meat-type and egg-laying birds. The virus replicates not only in the epithelium of upper and lower respiratory tract tissues, but also in many tissues along the alimentary tract and elsewhere e.g. kidney, oviduct and testes. It can be detected in both respiratory and faecal material. There is increasing evidence that IBV can infect species of bird other than the chicken. Interestingly breeds of chicken vary with respect to the severity of infection with IBV, which may be related to the immune response. Probably the major reason for the high profile of IBV is the existence of a very large number of serotypes. Both live and inactivated IB vaccines are used extensively, the latter requiring priming by the former. Their effectiveness is diminished by poor cross-protection. The nature of the protective immune response to IBV is poorly understood. What is known is that the surface spike protein, indeed the amino-terminal S1 half, is sufficient to induce good protective immunity. There is increasing evidence that only a few amino acid differences amongst S proteins are sufficient to have a detrimental impact on cross-protection. Experimental vector IB vaccines and genetically manipulated IBVs--with heterologous spike protein genes--have produced promising results, including in the context of in ovo vaccination.

Detection of Massachusetts and Arkansas serotypes of infectious bronchitis virus in broilers

The objective of this study was to compare the presence of the Arkansas (Ark) and Massachusetts (Mass) serotypes of infectious bronchitis virus (IBV) in the tracheas and cecal tonsils of commercial broilers after vaccination at 1 day of age by coarse spray. When given as a single serotype vaccine, the Mass strain was detected by reverse transcriptase-polymerase chain reaction (RT-PCR)-restriction fragment length polymorphism (RFLP) only in the tracheas, whereas the Ark strain was detected in both the tracheas and cecal tonsils. By in situ hybridization, the Mass and Ark nucleocapsid (Nc) genes were detected only at 7 days in the tracheas. When both strains were given in the mixed vaccine, the Mass strain was more consistently detected by RT-PCR-RFLP in the tracheas and cecal tonsils at early stages of infection (up to 14 days) and the Arkansas strain was more consistently detected at late stages of infection (21 and 28 days). By in situ hybridization, the IBV Nc gene was more consistently detected in the trachea at early stages of infection (7, 14, and 21 days) and in the cecal tonsils at late stages of infection (21, 28, and 35 days). In general, the Mass strain was more frequently recovered from the tracheal and cecal tonsil tissues at earlier stages of infection and the Ark strain was recovered at later stages of infection.

Detection of Infectious Bronchitis Virus and Specific Anti- Viral Antibodies Using a Concanavalin A–Sandwich–ELISA

Concanavalin A-Sandwich ELISA (Con A-S-ELISA) was developed for the detection of infectious bronchitis virus (IBV) or chicken specific anti-viral antibodies. The antigen detection limit for the Con A-S-ELISA was 10(5,1) EID(50)/mL. Three homologous and four heterologous IBV strains were similarly detected. This assay was highly effective in detecting the virus after infected tissue homogenates were passed once in embryonated chicken eggs, showing a good agreement with virus isolation technique. The Con A-S-ELISA was also used to measure anti-IBV chicken antibodies and showed a high coefficient of correlation (r = 0.85) and an agreement of k = 0.80 with the commercially available Indirect-ELISA. The relative sensitivity and specificity between these two tests were, respectively, 92.86% and 95.65% with an accuracy of 93.39%. Thus, the Con A-S-ELISA proved to be able to detect alternatively homologous and heterologous IBV strains or specific chicken anti- IBV antibodies, using the Con A as capture reagent of this assay.

Severe acute respiratory syndrome vaccine development: experiences of vaccination against avian infectious bronchitis coronavirus

Vaccines against infectious bronchitis of chickens (Gallus gallus domesticus) have arguably been the most successful, and certainly the most widely used, of vaccines for diseases caused by coronaviruses, the others being against bovine, canine, feline and porcine coronaviruses. Infectious bronchitis virus (IBV), together with the genetically related coronaviruses of turkey (Meleagris gallopovo) and ring-necked pheasant (Phasianus colchicus), is a group 3 coronavirus, severe acute respiratory syndrome (SARS) coronavirus being tentatively in group 4, the other known mammalian coronaviruses being in groups 1 and 2. IBV replicates not only in respiratory tissues (including the nose, trachea, lungs and airsacs, causing respiratory disease), but also in the kidney (associated with minor or major nephritis), oviduct, and in many parts of the alimentary tract--the oesophagus, proventriculus, duodenum, jejunum, bursa of Fabricius, caecal tonsils (near the distal end of the tract), rectum and cloaca (the common opening for release of eggs and faeces), usually without clinical effects. The virus can persist, being re-excreted at the onset of egg laying (4 to 5 months of age), believed to be a consequence of the stress of coming into lay. Genetic lines of chickens differ in the extent to which IBV causes mortality in chicks, and in respect of clearance of the virus after the acute phase. Live attenuated (by passage in chicken embryonated eggs) IBV strains were introduced as vaccines in the 1950s, followed a couple of decades later by inactivated vaccines for boosting protection in egg-laying birds. Live vaccines are usually applied to meat-type chickens at 1 day of age. In experimental situations this can result in sterile immunity when challenged by virulent homologous virus. Although 100% of chickens may be protected (against clinical signs and loss of ciliary activity in trachea), sometimes 10% of vaccinated chicks do not respond with a protective immune response. Protection is short lived, the start of the decline being apparent 9 weeks after vaccination with vaccines based on highly attenuated strains. IBV exists as scores of serotypes (defined by the neutralization test), cross-protection often being poor. Consequently, chickens may be re-vaccinated, with the same or another serotype, two or three weeks later. Single applications of inactivated virus has generally led to protection of <50% of chickens. Two applications have led to 90 to 100% protection in some reports, but remaining below 50% in others. In practice in the field, inactivated vaccines are used in laying birds that have previously been primed with two or three live attenuated virus vaccinations. This increases protection of the laying birds against egg production losses and induces a sustained level of serum antibody, which is passed to progeny. The large spike glycoprotein (S) comprises a carboxy-terminal S2 subunit (approximately 625 amino acid residues), which anchors S in the virus envelope, and an amino-terminal S1 subunit (approximately 520 residues), believed to largely form the distal bulbous part of S. The S1 subunit (purified from IBV virus, expressed using baculovirus or expressed in birds from a fowlpoxvirus vector) induced virus neutralizing antibody. Although protective immune responses were induced, multiple inoculations were required and the percentage of protected chickens was too low (<50%) for commercial application. Remarkably, expression of S1 in birds using a non-pathogenic fowl adenovirus vector induced protection in 90% and 100% of chickens in two experiments. Differences of as little as 5% between the S1 sequences can result in poor cross-protection. Differences in S1 of 2 to 3% (10 to 15 amino acids) can change serotype, suggesting that a small number of epitopes are immunodominant with respect to neutralizing antibody. Initial studies of the role of the IBV nucleocapsid protein (N) in immunity suggested that immunization with bacterially expressed N, while not inducing protection directly, improved the induction of protection by a subsequent inoculation with inactivated IBV. In another study, two intramuscular immunizations of a plasmid expressing N induced protective immunity. The basis of immunity to IBV is not well understood. Serum antibody levels do not correlate with protection, although local antibody is believed to play a role. Adoptive transfer of IBV-infection-induced alphabeta T cells bearing CD8 antigen protected chicks from challenge infection. In conclusion, live attenuated IBV vaccines induce good, although short-lived, protection against homologous challenge, although a minority of individuals may respond poorly. Inactivated IBV vaccines are insufficiently efficacious when applied only once and in the absence of priming by live vaccine. Two applications of inactivated IBV are much more efficacious, although this is not a commercially viable proposition in the poultry industry. However, the cost and logistics of multiple application of a SARS inactivated vaccine would be more acceptable for the protection of human populations, especially if limited to targeted groups (e.g. health care workers and high-risk contacts). Application of a SARS vaccine is perhaps best limited to a minimal number of targeted individuals who can be monitored, as some vaccinated persons might, if infected by SARS coronavirus, become asymptomatic excretors of virus, thereby posing a risk to non-vaccinated people. Looking further into the future, the high efficacy of the fowl adenovirus vector expressing the IBV S1 subunit provides optimism for a live SARS vaccine, if that were deemed to be necessary, with the possibility of including the N protein gene.

Development of an ELISA for detection of antibodies to avian reovirus in chickens

An enzyme-linked immunosorbent assay (ELISA) using the expressed sigmaC and sigmaB proteins which induce neutralizing antibodies as the coating antigen (sigmaC-sigmaB-ELISA) for the detection of antibodies to avian reovirus in chickens was developed and compared with serum neutralization and conventional ELISA tests. These assays were used to examine the sera from chickens vaccinated experimentally and farm chickens. The correlation rate between serum neutralization and a sigmaC-sigmaB-ELISA was 100% (156/156), and that between serum neutralization and conventional ELISA was 89.1% (139/156). The results revealed that preparation of an ELISA by using sigmaC and sigmaB of ARV as the coating antigen in detecting the field chicken sera in comparison with the conventional ELISA gave a titer more correlated to the serum neutralization test. The sigmaC-sigmaB-ELISA showed a higher correlation with the serum neutralization-positive and -negative sera than that obtained with conventional ELISA. This combination antigen may thus be the best suited for preparing an ELISA for improving the determination of the immune status of chicken flocks or for detection of chicken infections with avian reovirus.

Production of monoclonal antibodies against conserved components of infectious bronchitis virus

Murine hybridomas producing IgG1 monoclonal antibodies (Mabs) against N and S2 proteins (53KDa and 82KDa, respectively) from avian infection bronchitis virus (IBV) strain M41 were generated by the fusion of a myeloma cell line (Sp2/0-Ag14) with spleen cells from Balb/c mice previously immunized with whole virus IBV M41. Post-fusion screening criterion was by ELISA and 36 positive hybrids were generated after fusions. Two hybrids specific to N (N3F10) and S2 (S12B2) proteins from M41 (serotype Massachusetts) were selected by western blotting. These Mabs recognized the Ark-99 (serotype Arkansas) and A5968 (serotype Connecticut) IBV strains in addition to M41. By ELISA, the Mab against the S2 (S12B2) recognized all reference and Brazilian strains (M41, SE-17, H52, 297, 283, PM-1, PM-2, PM-3, 351, 29-78 E 327) studied, while the Mab against N recognized only six (M41, SE-17, H52, 283, 327 e 297) strains. The Mab against S2 may become a useful tool for IBV detection on the routine diagnosis of infectious bronchitis, especially for helping the differential diagnosis of clinically and pathologically confusing diseases, while the Mab against N (N3F10) recognized a probably less conserved region among the strains and may be interesting to comparing IBV isolates.

An enzyme-linked immunosorbent assay for the detection of antibody to avian reovirus by using protein sigma B as the coating antigen

An enzyme-linked immunosorbent assay using the expressed protein sigma B as the coating antigen (sigma B-ELISA) for detecting antibody to avian reovirus (ARV) in chickens was developed and compared with a conventional ELISA. Both ELISA s and a serum neutralisation (SN) test were used to test the sera from experimentally vaccinated and farm chickens. The sigma B-ELISA could clearly distinguish the SN-positive and -negative sera in 38-week-old chickens. The correlation rate between SN and a sigma B-ELISA was 100 per cent (65/65), and that between SN and conventional ELISA was 84 per cent (55/65). With the sigma B-ELISA, all SN-negative sera had low absorbance values (below 0.06), and the absorbance values correlated closely with the SN titres. However, the sera which were antibody-negative by SN had various absorbance values, ranging from 0.07 to 0.39 in the conventional ELISA. Hence, the sigma B-ELISA had lower non-specific binding reactions than the conventional ELISA against sera from ARV -negative birds. Antibody against ARV could be detected by sigma B-ELISA after vaccination. Absorbance values peaked 4 weeks after vaccination at 2 weeks of age and were maintained until the birds were 27 weeks old. The results suggest that the presence of antibody against viral protein sigma B in birds may be used as a good indicator by the sigma B - ELISA for detecting immune status of a chicken flock or to detect chickens infected with ARV.

Infectious bronchitis virus: Immunopathogenesis of infection in the chicken

The immunopathogenesis of infectious bronchitis virus (IBV) infection in the chicken is reviewed. While infectious bronchitis (IB) is considered primarily a disease of the respiratory system, different IBV strains may show variable tissue tropisms and also affect the oviduct and the kidneys, with serious consequences. Some strains replicate in the intestine but apparently without pathological changes. Pectoral myopathy has been associated with an important recent variant. Several factors can influence the course of infection with IBV, including the age, breed and nutrition of the chicken, the environment and intercurrent infection with other infectious agents. Immunogenic components of the virus include the S (spike) proteins and the N nucleoprotein. The humoral, local and cellular responses of the chicken to IBV are reviewed, together with genetic resistance of the chicken. In long-term persistence of IBV, the caecal tonsil or kidney have been proposed as the sites of persistence. Antigenic variation among IBV strains is related to relatively small differences in amino acid sequences in the S1 spike protein. However, antigenic studies alone do not adequately define immunological relationships between strains and cross-immunisation studies have been used to classify IBV isolates into 'protectotypes'. It has been speculated that changes in the S1 protein may be related to differences in tissue tropisms shown by different strains. Perhaps in the future, new strains of IBV may arise which affect organs or systems not normally associated with IB.

Local antibody production in the oviduct and gut of hens infected with a variant strain of infectious bronchitis virus

Following infection of 16-week old specific pathogen-free (SPF) female chickens with an enterotropic variant of infectious bronchitis virus (IBV) strain G, IBV-specific Immunoglobulin G (IgG) and IgA were detected in tears, tracheal washes, oviduct washes, duodenal and caecal contents using class-specific monoclonal antibodies in enzyme linked immunosorbent assays (ELISA). IgG antibody content was highest in tears on Day 7 post-infection (p.i.) and was still detectable on Day 23 p.i. Significant levels of IgG antibody were present in oviduct washes on Days 7 and 23 p.i. Tears showed the highest IgA antibody concentration of any sample on Day 7 p.i. but this decreased to an insignificant level by Day 17 p.i. Oviduct and tracheal washes had IgA antibodies on Day 7 p.i. Significant levels of both antibody classes were detected in duodenal contents on Day 17 p.i. only but neither was present in caecal contents. Using a method which compares titre of antibody produced from pieces of tissue at 4 degrees C with that at 37 degrees C as an indicator of local secretion, IgG and IgA antibody synthesis was demonstrated in the Harderian gland on Days 7 and 17 p.i. Local IgG antibody synthesis was seen in the oviduct on Day 7 p.i. but on Day 23 p.i. the optical density at 4 degrees C was higher than at 37 degrees C, suggestive of high concentrations of extracellular antibody. In a separate experiment, passively administered IBV antibody transuded from serum into oviduct washes but did not do so in the trachea. In a third experiment, ELISA and haemagglutination-inhibition (HI) titres of serum and oviduct washes from ten hens previously infected when day-old were compared with egg production. Maximum positive correlation was seen between HI titres of oviduct washes and egg production.

Serological diagnosis of Salmonella serotype enteritidis infections in poultry by ELISA and other tests

Serological methods have increasingly been used for the detection of invasive Salmonella serotypes including enteritidis in poultry. Different types of ELISA, particularly indirect or double antibody-blocking assays using a variety of antigens such as lipopolysaccharide, flagella and SEF14 fimbrial antigen are used as part of control programmes in a number of countries. There are many advantages to using such assays for preliminary screening of flocks prior to using bacteriological culture methods.

Serum, disc and egg ELISA for the serodiagnosis of Salmonella gallinarum and S. enteritidis infections in chickens

An ELISA was evaluated for the serodiagnosis of fowl typhoid and paratyphoid due to Salmonella enteritidis in chickens. The hot phenol: water lipopolysaccharide (LPS) extract of Salmonella was used as the antigen. Chicken serum, eggs and discs impregnated with chicken blood were tested for the presence of antibodies against Salmonella factor 'O' 9 antigen. The substrate and chromogen used were hydrogen peroxide and orthophenylenediamine respectively. Serological results from the experimentally and naturally infected chickens showed close agreement between the conventional Serum Tube Agglutination Test (SAT) and serum ELISA while serum ELISA results were in close agreement with the egg and disc ELISA results. It was noted that ELISA was highly sensitive, convenient and versatile. It is concluded that ELISA, especially disc ELISA, ought to replace SAT for seroscreening chickens against S. gallinarum and other Salmonella Group D infections.

ELISAs and the serological analysis of Salmonella infections in poultry: a review

Large increases in the number of cases of human food-poisoning caused by salmonella have occurred in several countries in recent years. In England and Wales the annual number of bacteriologically confirmed cases rose from 10665 in 1981 to 30112 in 1990 and it is generally accepted that these figures are underestimates. The reasons for the unprecedented increase are largely unknown but may include increases in the consumption of convenience foods, poultry, and poultry products, together with a dramatic increase inSalmonella enteritidisinfections in poultry.S. enteritidisandS. typhimuriumare now the predominant serotypes both in human disease and in poultry.

Envelope proteins of avian infectious bronchitis virus: purification and biological properties

Immunoadsorbents, made with monoclonal antibodies, were used to purify the spike and membrane proteins of infectious bronchitis virus (IBV). The purified proteins were inoculated into rabbits to produce antisera. The rabbit anti-spike sera neutralized the infectivity of the virus whereas the anti-membrane sera did not. IBV-infected chickens produced antibodies to both the spike and membrane proteins. Both these antibodies were at their highest concentration about 9-11 days after inoculation, whereas neutralizing antibodies were present only at very low concentrations at that time. Neutralizing antibodies were at their highest concentration 21 days after inoculation. A second inoculation of virus at 42 days induced an anamnestic antibody response to the spike and membrane proteins and also for the neutralizing antibodies. The neutralizing, anti-spike and anti-membrane antibodies all reached highest concentrations 7-11 days after this inoculation. The advantages of purifying viral proteins using affinity chromatography with monoclonal antibodies are discussed.

Applications of enzyme-linked immunosorbent assay in veterinary medicine: a bibliography

During the last decade enzyme-linked immunosorbent assay has been a technique of major interest to those engaged in immunodiagnostics of human and animal diseases. Owing to its simplicity, specificity and sensitivity it has taken precedence over other conventional assays, including radioimmunoassay on the grounds of freedom from radiation hazards. Many applications of this assay have been developed in veterinary medicine and they are listed in this article.

The use of an enzyme-linked immunosorbent assay to detect IgG antibodies to serotype-specific and group-specific antigens of fowl adenovirus serotypes 2, 3 and 4

A sensitive enzyme-linked immunosorbent assay (ELISA) has been developed which can detect serotype and group-specific antibodies (IgG) to fowl adenovirus serotypes 2, 3 and 4. The chickens produced principally type-specific antibodies after a single oral inoculation of virus which enabled that strain to be identified by the ELISA. However, inoculation of an heterologous serotype, although inducing strain-specific antibodies to itself, also induced high levels of antibody to the group-specific antigens. This masked the serotype-specific antibodies in the ELISA to the first serotype. The ELISA, which has similar sensitivity to the serum neutralisation test, could be used as a rapid, easily performed test to identify fowl adenovirus-specific antibodies.

Comparison of a microneutralisation test with ELISA and precipitin tests for detection of antibodies to infectious bronchitis virus in chickens

A microneutralisation test for infectious bronchitis virus using virus antigens available in Australia, cell culture medium containing low concentrations of serum and an elevated incubation temperature is described. The technique was economical on reagents and of comparable sensitivity to the enzyme-linked immunosorbent assay (ELISA). The value of the microneutralisation, ELISA and precipitin tests in assessing the serological response of a flock of commercial chickens to vaccine and natural virus challenge was determined.

Avian Infectious Bronchitis Virus

This chapter provides an overview of the classification, description, hosts, key developments, diagnostic techniques, and diagnostic reagents for avian infectious bronchitis virus. Avian infectious bronchitis virus belongs to the family Coronaviridae; genus Coronavirus; and species Avian infectious bronchitis virus. The virus causes acute contagious respiratory illness and includes reproductive tissue disease in chickens. The hosts of avian infectious bronchitis virus are only chickens. Avian infectious bronchitis disease was first reported in the United States. Vaccines for this disease were developed in the 1950s and the economic impact diminished. The diagnostic techniques for avian infectious bronchitis virus are virus neutralisation (VN), agar gel immunodiffusion (AGID), fluorescent antibody (FA), compliment fixation (CF), and enzyme-linked immunosorbent assay (ELISA).