Manipulation of the infectious bronchitis coronavirus genome for vaccine development and analysis of the accessory proteins

Infectious bronchitis coronavirus (IBV) is the cause of the single most economically costly infectious disease of domestic fowl in the UK—and probably so in many countries that have a developed poultry industry. A major reason for its continued dominance is its existence as many serotypes, determined by the surface spike protein (S), cross-protection being poor. Although controlled to some degree by live and inactivated vaccines, a new generation of IB vaccines is called for. Reverse genetic or ‘infectious clone’ systems, which allow the manipulation of the IBV genome, are key to this development. New vaccines would ideally be: genetically stable (i.e. maintain a stable attenuated phenotype); administered in ovo; and be flexible with respect to the source of the spike protein gene. Rational attenuation of IBV requires the identification of genes that are simultaneously not essential for replication and whose absence would reduce pathogenicity. Being able to modify a ‘core’ vaccine strain to make it applicable to a prevailing serotype requires a procedure for doing so, and the demonstration that ‘spike-swapping’ is sufficient to induce good immunity.

We have demonstrated that four small IBV proteins, encoded by genes 3 and 5, are not essential for replication; failure to produce these proteins had little detrimental affect on the titre of virus produced. Our current molecularly cloned IBV, strain Beaudette, is non-pathogenic, so we do not know what effect the absence of these proteins would have on pathogenicity. That said, plaque size and composition of various gene 3/5 recombinant IBVs in cell culture, and reduced output and ciliostasis in tracheal organ cultures, shows that they are less aggressive than the wild-type Beaudette. Consequently these genes remain targets for rational attenuation. We have recently obtained evidence that one or more of the 15 proteins encoded by gene 1 are also determinants of pathogenicity. Hence gene 1 is also a target for rational attenuation.

Replacing the S protein gene of Beaudette with that from the pathogenic M41 strain resulted in a recombinant virus that was still non-pathogenic but which did induce protection against challenge with M41. We have since made other ‘spike-swapped’ recombinants, including ones with chimaera S genes. Uniquely, our molecular clone of Beaudette is benign when administered to 18-day-old embryos, even at high doses, and induces immunity after this route of vaccination.

Taken together, our results point to the creation of a new generation of IB vaccines, based on rational modification of the genome, as being a realisable objective.

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.

Infectious bronchitis virus: S1 gene characteristics of vaccines used in China and efficacy of vaccination against heterologous strains from China

The entire S1 protein genes of eight infectious bronchitis (IB) vaccine strains used in China were compared with those of the IB virus isolates present in the field in China. The nucleotide and amino acid similarities between the eight IB vaccine strains and the field strain, tl/CH/LDT3/03, which was isolated from a teal (Anas sp.), were not more than 81.1% and 79.2%, respectively. Phylogenetic analysis based on the S1 genes showed that the vaccines and field strains belonged to different clusters and showed larger evolutionary distances, and indicated that they were of different genotypes. Four out of the eight vaccines, in addition to the Massachusetts type vaccine H120, were used for protection tests against challenge by the IB virus isolate tl/CH/LDT3/03. This revealed that each of the five IB vaccines induced poor protection against the teal isolate, as assessed by respiratory protection, clinical signs and mortality, indicating the necessity of developing vaccines from local strains for IB control in China.

Infectious bronchitis virus serotypes in poultry flocks in Jordan

Infectious bronchitis virus (IBV) causes respiratory disease in chickens all over the world. IBV has many serotypes that do not confer cross protection against each other. Hemagglutination inhibition (HI) test has been used to determine the serotypes of IBV as a substitute to the more laborious virus neutralization test and the more sophisticated restriction endonuclease digestion or sequencing of the S1 gene. In Jordan, no previous studies have been carried out to determine the involvement of IBV in respiratory disease in chickens, or the serotypes of IBV that possibly exist. In this study, serum from different chicken flocks (n=20) that suffered from respiratory disease were tested for IBV antibodies using commercial IBV antibody ELISA at time of the initial signs of the respiratory disease and repeated on serum samples from the same flocks 10-14 days later. ELISA titer for IBV increased in 14 out of 20 flocks (70%) after 10-14 days of the initial signs of the respiratory disease and this indicates a recent exposure to IBV. The second serum samples from these 14 flocks were further examined against a panel of five IBV antigens (Ark, Conn, DE-072, JMK, and Mass) by HI test to determine the serotype(s) of IBV they have been exposed to. The HI test results indicated that the exposure of some of these flocks were to Ark, DE-072, and Mass like serotypes. However, the HI titers against the antigens used in this study were relatively similar in 10 out of the 14 flocks (71%) and the serotype of IBV that these flocks were exposed to could not be determined and the possible causes of this are discussed.

Epididymal Stone Formation and Decreased Sperm Production in Roosters Vaccinated with a Killed Strain of Avian Infectious Bronchitis Virus

Our objective was to determine if vaccination with killed avian infectious bronchitis virus (AIBV) causes epididymal calcium stones in the rooster as is seen following vaccination with live attenuated AIBV. Specific-pathogen-free roosters were divided into three groups: nonvaccinated (NONVAC), live attenuated AIBV-vaccinated (LVAC), and killed AIBV-vaccinated (KVAC) groups. Roosters were vaccinated at 2, 6, 10, and 14 wk of age and the epididymal region was observed at 27 wk of age. Epididymal stones were present in 13% of NONVAC, 50% of KVAC, and 64% of LVAC roosters. Histologically, immune cells were seen in the interstitium of efferent ductules containing stones. We conclude that use of a killed vaccine does not reduce the incidence of epididymal stones.

S1 gene sequence analysis of a nephropathogenic strain of avian infectious bronchitis virus in Egypt

BACKGROUND

Infectious bronchitis is highly contagious and constitutes one of the most common and difficult poultry diseases to control. IBV is endemic in probably all countries that raise chickens. It exists as dozens of serotypes/genotypes. Only a few amino acid differences in the S1 protein of vaccine and challenge strains of IBV may result in poor protection. Tropism of IBV includes the respiratory tract tissues, proventriculus and caecal tonsils of the alimentary tract, the oviduct and the kidney.

RESULTS

Infectious bronchitis virus (IBV) strain closely related to Massachusetts (Mass) serotype was isolated from broiler chickens suffering from severe renal and respiratory distresses. The isolate was serologically identified by Dot-ELISA and further characterized by RT-PCR then genotyped using S1 gene sequence analysis. Alignment of the S1 sequence of the isolate with 16 IBV strains revealed high homology to isolates related to Mass serotype. Inoculation with the strain reproduced the disease in experimental 1-day-old chickens and resulted in 20% mortality, severe renal and moderate respiratory distresses. Marked histopathological changes in both kidney and trachea were observed in experimentally infected chickens. A protection study using the H120 live attenuated vaccine showed low protection rate in spite of high S1 sequence homology (97%). Protection based criteria were: virus re-isolation attempts from trachea, tracheal and renal histopathology as well as IBV antigens detection by immunofluorescent antibody technique in kidney sections.

CONCLUSION

Periodical evaluation of cross-protective capabilities of IBV vaccine(s) versus recently recovered field isolates should be performed to ensure optimum control of IBV.

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.

Maternal antibody transfer from dams to their egg yolks, egg whites, and chicks in meat lines of chickens

Maternal antibodies are transferred from hens to the chicks via the egg. To gain insight into maternal antibody transfer and endogenous production of antibodies in broiler chicks, total IgY, IgA, IgM, as well as anti-Newcastle disease virus (NDV) and anti-infectious bronchitis (IBV) antibody levels were examined in the dams' plasma, egg yolks, egg whites, and chicks' plasma on d 3, 7, 14, and 21. Blood was collected from 39-wk-old breeder hens (line 1, n = 17; line 2, n = 21). Fertile eggs were used for antibody extraction from the egg yolks and egg whites (4 to 5 eggs/dam) and for hatching. Unvaccinated chicks (4 to 5 chicks/dam) were reared in a HEPA-filtered room and were bled on d 3, 7, 14 and 21. Based on ELISA methods, plasma levels of IgY and IgM were higher (P < 0.0001), and those of IgA were similar (P = 0.31), in line 2 compared with line 1. Egg yolk IgY and IgA, as well as egg white IgY, IgA, and IgM levels were higher in line 2 compared with line 1 (P < 0.0001). Independent of line of chicken, the percentage dam-to-chick (3 d) plasma transfer of IgY was estimated to be approximately 30%, with that for IgM and IgA less than 1%. Chicks synthesized IgM first, followed by IgA and IgY. Anti-NDV and anti-IBV antibodies were detected in the dams' plasma, egg yolks, and in the chicks' plasma on d 3 and 7, with line 2 having higher anti-IBV and lower anti-NDV levels than line 1 in all samples (P < 0.0001). In summary, IgY levels, total or antigen-specific, in the dams' plasma or eggs were found to be a direct indicator of maternal antibody transfer to the chicks' circulation, with an expected percentage transfer of approximately 30%. This knowledge, together with the observed time course of endogenous antibody production in broiler chicks, may find direct application in formulating strategies for protecting chicks, especially during the first few weeks of age when their immune system is not yet fully functional.

Genotypic and phenotypic characterization of the California 99 (Cal99) variant of infectious bronchitis virus

The California 99 (Cal99) variant of infectious bronchitis virus (IBV) was first recovered in 1999 from vaccinated broiler chicken flocks in Central California. The S1 hypervariable region of Cal99 genome was most closely related to Arkansas (Ark) serotype viruses. In this study, the complete genome of Cal99 was sequenced, and the structural protein genes were compared with those of commonly used IBV vaccines as well as those of isolates from naturally occurring outbreaks in different parts of the world, to elucidate potential sources of genetic material. Based on sequence comparison, the prototype Cal99 virus is similar to the apathogenic ArkDPI virus, except in the S1 gene and stretches of sequence in the S2 and M structural protein genes, which are more related to Connecticut (Conn) and Massachusetts (Mass) strain viruses, respectively. We speculate that these two fragments came from a Conn and a Mass virus, respectively, and were incorporated into a virus largely derived from ArkDPI. Since Ark, Conn and Mass strains have been simultaneously used as live vaccines in California, both point mutations and recombination among vaccine strains may have contributed to the emergence of the Cal99 variant virus. Analysis of the structural protein genes of six Cal99 isolates demonstrated that viruses of this serotype may differ substantially in the non-S1 structural genes. Finally, we performed a challenge study with Cal99 and demonstrated that the virus causes late-onset respiratory disease, with a severity comparable to that of the M41 IBV challenge strain.

Detection of antibodies to avian infectious bronchitis virus by a recombinant nucleocapsid protein-based enzyme-linked immunosorbent assay

The recombinant antigen obtained by cloning and expressing two IBV nucleocapsid protein fragments (143-414 aa, 281-414 aa) in Escherichia coli was used for the detection of avian infectious bronchitis virus (IBV) specific antibodies in chicken sera by the indirect ELISA (rNpIBV-ELISA). As a result of testing 1524 serum samples the diagnostic sensitivity and specificity of rNpIBV-ELISA when comparing those of the routine whole IBV ELISA have been shown to be 93.81% and 87.36%, respectively. The agreement value was 91.5%.

Safety and efficacy of an infectious bronchitis virus used for chicken embryo vaccination

Commercial vaccines for in ovo vaccination have not yet been developed for infectious bronchitis virus (IBV), the major coronavirus in the poultry industry. Recombinant IBVs based on the Beaudette strain expressing the Beaudette spike protein (Beau-R) or that from the virulent M41 strain (BeauR-M41(S)) were assessed for their potential as prototype vaccines for application to 18-day-old embryos. Pathogenicity was assessed by observing the effect on hatchability, and/or the production of nasal discharge and/or the effects on ciliary activity in the trachea at various time points post hatch. In contrast to commercial IBV vaccines given in ovo, the Beau-R and BeauR-M41(S) strains did not reduce hatchability or cause nasal discharge, and caused minimal damage to the ciliated epithelium of the trachea. The presence of the spike protein from a virulent virus did not increase the pathogenicity of the virus according to the criteria used. Assessment of the BeauR-M41(S) strain for efficacy showed that it protected up to 90% of chicks against challenge with virulent IB virus (M41) in a dose dependent manner. Further egg passage of the BeauR-M41(S) strain (BeauR-M41(S) EP10) did not increase its pathogenicity though it did improve its efficacy, based on serology and protection against a virulent challenge. BeauR-M41(S) EP10 was more efficacious than BeauR-M41(S) protecting more birds against virulent challenge and providing a better serological antibody response. BeauR-M41(S) EP10 induced a serological response similar to that of a commercial vaccine given at day-old though the commercial vaccine provided slightly higher efficacy. These results are promising for the development of embryo safe efficacious IBV vaccines for in ovo application.

Reciprocal Antibody and Complement Responses of Two Chicken Breeds to Vaccine Strains of Newcastle Disease Virus, Infectious Bursal Disease Virus and Infectious Bronchitis Virus

Serum antibody responses and haemolytic complement activity were evaluated in White Leghorn (WLH) and Rhode Island Red (RIR) chickens that were vaccinated with live-attenuated vaccines of Newcastle disease virus, or infectious bronchitis virus, or infectious bursal disease virus by means of ocular challenge at 10 times the normal vaccination dose. Complement titres in non-vaccinated birds were significantly higher in WLH birds compared to RIR birds. The lentogenic viral infection resulted in an immediate stimulation of complement activity, followed by a decrease to initial complement levels within 2 weeks post vaccination, when the antibody response took over immune defence. As compared to WLH chickens, RIR birds mounted a faster and significantly higher antibody response to the vaccine viruses used. In WLH hens, significantly higher haemolytic complement activity post vaccination was found as compared to RIR hens. Possible consequences of the observed differences in immune responsiveness of the two breeds to viral vaccines are discussed.

Diseases of indigenous chickens in Bokaa village, Kgatleng district, Botswana

his study examined flock size and management, level of internal and external parasite burden and seroprevalence of antibodies to poultry pathogens in indigenous chickens in Bokaa village, Kgatleng district, Botswana. The mean flock size was 22.6±6.85 with a range of 11-34. The mean body weights of cocks and hens were 2.28±0.56 kg and 1.70 ±0.38 kg, respectively. Housing and commercial poultry feed were not provided. Ascaridia galli, Heterakis gallinarum and Syngamus trachea were found in some birds. Although the chickens were not vaccinated against any poultry diseases, serum antibodies to Newcastle disease, infectious bursal disease and infectious bronchitis were detected.

Structure- and oil type-based efficacy of emulsion adjuvants

Oil-based emulsions are well-known immunopotentiators for inactivated, "killed" vaccines. We addressed the relationship between emulsion structure and levels of in vivo antibody formation to inactivated New Castle Disease virus (NDV) and Infectious Bronchitis virus (IBV) as antigens in 3-week-old chickens. The use of a polymeric emulsifier allowed for direct comparison of three types of emulsions, water-in-oil (W/O), oil-in-water (O/W) and W/O-in-water (W/O/W), while maintaining an identical content of components for each vehicle. They were prepared with either non-metabolizable, mineral oil or metabolizable, Miglyol 840. In addition, we assessed the inherent release capacity of each emulsion variant in vitro. Remarkably, we noted that W/O-type emulsions induced the best immune responses, while they released no antigen during 3 weeks. In general, mineral oil vaccines showed superior efficacy compared to Miglyol 840-based vaccines.

Infectious bronchitis virus S1 gene sequence comparison is a better predictor of challenge of immunity in chickens than serotyping by virus neutralization

Five strains of infectious bronchitis virus isolated from commercial chickens from the state of Pennsylvania, USA during the years 1998 and 1999 were studied. The strains were selected for cross-challenge in specific pathogen free chickens and virus neutralization in chick embryos on the basis of partial S1 sequence amino acid identity values. The partial sequences analysed spanned the hypervariable amino terminus region of S1 from amino acid residues 48 to 219, based on the Beaudette strain. Using their S1 identity values, the strains represented a continuum of genetic, and thus antigenic, relationships. When compared with strain PA/5083/99, strain PA/Wolgemuth/98 had high sequence identity (96%) followed by PA/171/99 (85%), PA/5344/98 (70%) and PA/1220/98 (34%). The method of Archetti and Horsfall was used for calculating antigenic relatedness values of virus neutralization tests. The same formula was also applied to the percentage protection values of cross-challenge tests to derive protective relatedness values among the strains. The antigenic relatedness values, protective relatedness values, and the partial S1 sequence identity values were then analysed. The findings indicated partial S1 sequence identity values were more strongly correlated with protective relatedness values and than antigenic relatedness values.

Antigenic and molecular characterization of isolates of the Italy 02 infectious bronchitis virus genotype

As part of an epidemiological surveillance of infectious bronchitis virus (IBV) in Spain, four Spanish field isolates showed high S1 spike sequence similarities with an IBV sequence from the GenBank database named Italy 02. Given that little was known about this new emergent IBV strain we have characterized the four isolates by sequencing the entire S1 part of the spike protein gene and have compared them with many reference IBV serotypes. In addition, cross-virus neutralization assays were conducted with the main IBV serotypes present in Europe. The four Spanish field strains and the Italy 02 S1 sequence from the NCBI database were established as a new genotype that showed maximum amino acid identities with the 4/91 serotype (81.7% to 83.7%), the D274 group that included D207, D274 and D3896 strains (79.8% to 81.7%), and the B1648 serotype (79.3% to 80%). Furthermore, on the basis of these results, it was demonstrated that the Italy 02 genotype had been circulating in Spain since as early as 1997. Based on the average ratio of synonymous:non-synonymous (dS/dN) amino acid substitutions within Italy 02 sequences, no positive selection pressures were related with changes observed in the S1 gene. Moreover, phylogenetic analysis of the S1 gene suggested that the Italy 02 genotype has undergone a recombination event. Virus neutralization assays demonstrated that little antigenic relatedness (less than 35%) exists between Italy 02 and some of the reference IBV serotypes, and indicated that Italy 02 is likely to be a new serotype.

Rapid differentiation of current infectious bronchitis virus vaccine strains and field isolates in Australia

OBJECTIVE

Rapid differentiation of vaccine strains of infectious bronchitis virus (IBV) from wild type strains would enhance investigations of disease outbreaks. This study aimed to develop a reverse transcription-polymerase chain reaction (RT-PCR) assay to differentiate between Australian vaccine strains of IBV and field isolates.

PROCEDURE

A fragment of 6.5 kilobases that contains the S, M and N genes was amplified by RT-PCR from ten different IBV strains, including vaccine strains and field isolates, and then sequenced.

RESULTS

Comparison of the sequences of these strains revealed a deletion of 58 bases in the 3' untranslated region (UTR) of IBV vaccine strains but not in the field isolates. Two primers were designed to amplify a fragment of the 3' UTR that differed in size between the vaccine strains and field isolates. RT-PCR was performed using these two primers to screen 20 IBV strains, including field isolates and the vaccine strains. All strains were correctly identified as either vaccine strains or field isolates.

CONCLUSION

This procedure is a rapid, sensitive and inexpensive method for discrimination between most current Australian vaccine strains and field isolates of IBV.

Identification of one peptide which inhibited infectivity of avian infectious bronchitis virus in vitro

Purified avian infectious bronchitis virus (IBV) was used to screen a random phage display peptide library. After the fourth panning, 10 positive phages were sequenced and characterized. The phages specifically inhibited IBV infectivity in HeLa cells and blocked IBV haemagglutination. One linear peptide "GSH HRH VHS PFV" from the positive phages with the highest neutralization titer was synthesized and this peptide inhibited IBV infection in HeLa as well. The results may contribute to development of antiviral therapeutics for IBV and studying the determinants for viral and cell interaction.

Oral immunoadjuvant activity of Lactobacillus casei subsp. casei in dextran-fed layer chickens

We recently reported that synbiotic Lactobacillus casei subsp. casei together with specific substrate dextran elicited an enhancement in humoral immune response against bovine serum albumin (BSA) as a model antigen in BALB/c mice. The present study was designed to evaluate the oral immunoadjuvant effects of the synbiotic in layer chickens. Using a PCR assay, L. casei subsp. casei was detected specifically in the intestinal chyme of chickens (10 d of age, Julia strain) fed ad libitum on a diet supplemented with 75 mg dextran/kg (dextran-supplemented diet, DSD) and administered orally with 10(7) colony-forming units (CFU) L. casei subsp. casei in 0.1 ml PBS with the aid of an intubation needle at 1, 2 and 3 d of age. Furthermore, oral administration of 10(7) CFU L. casei subsp. casei at 1-3 d of age significantly enhanced the production of anti-BSA antibody in DSD-fed chickens (60 d of age) administered orally with 1 mg BSA at 32 and 33 d of age and subcutaneously with 5 microg BSA at 33 d of age. In addition, among bacterial numbers tested, 10(6) CFU L. casei subsp. casei together with dextran induced an effective increase in humoral immune response to mixed inactivated vaccines against Newcastle disease and avian infectious bronchitis, and the treatment may be advantageous in protecting against these infectious diseases in chickens in actual application. These results suggest that dietary supplementation of L. casei subsp. casei with dextran leads to immunomodulation of humoral immune responses.

Effect of IBV-H120 vaccination in broilers on colibacillosis susceptibility after infection with a virulent Massachusetts-type IBV strain

Vaccination against infectious bronchitis (IB) is aimed to protect against clinical IB. The question is, however, whether vaccinated birds are also protected against predisposure for colibacillosis after a subsequent IBV infection. We examined this research question in four experiments. One-day-old commercial broilers, housed in isolators, were vaccinated with IB vaccine strain H120 by coarse spray or ocularly. Twenty-eight days after vaccination, broilers were challenged with the virulent IBV strain M41. Five days later, broilers were inoculated with Escherichia coli strain 506. Body weight uniformity, severity of E. coli airsacculitis, and systemic E. coli infection at 7 days following E. coli inoculation were used as parameters for colibacillosis. IBV vaccination reduced both the number of broilers with E. coli airsacculitis as well as the severity of airsacculitis significantly after challenge with IBV-M41 and E. coli 506. However, in spray-vaccinated groups, no significant reduction of the number of birds with systemic colibacillosis or the severity of this infection was obtained, and body weight uniformity was not significantly improved compared with nonvaccinated, IBV-M41, and E. coli 506-challenged groups. Eye-drop vaccination resulted in conflicting results.

[Biological properties of the chick infectious bronchitis virus isolated in Russia]

A field chick infectious bronchitis virus (IBV) was isolated from the pathological material on chick embryos. The nucleotide sequence of the S1 gene was determined and comparatively analyzed with some sequences of this gene of foreign and Russian vaccine strains and isolates. A cross-neutralization test using sera to various IBV seroptypes was performed. The isolate was shown to antigenically differ from the reference strains. Bioassay was carried out, by using one-day chicks and the immunogenic properties of the virus were investigated.

Development of attenuated vaccines from Taiwanese infectious bronchitis virus strains

Due to variations in serotypes among different strains of avian infectious bronchitis viruses (IBV), vaccination of chicks with imported vaccines fails to protect them from IBV infections in Taiwan. Therefore, we develop attenuated vaccines from local strains in Taiwan. A Taiwan Group I (TW I) strain was passaged 74 times through specific pathogen-free (SPF) chicken embryonated eggs, and then tested in SPF chickens. The attenuated vaccine was not pathogenic in 1-week-old chicks, had a neutralization index (NI) of greater than 4.4 and efficacy of 90% when inoculated birds were challenged with a field IBV strain. Similar results were obtained for a vaccine made from a Taiwan Group II IBV strain. Additionally, the TW I attenuated vaccine strain had no reversion to virulence after five back passages in chicks. In conclusion, these attenuated vaccines have potential for controlling local Taiwanese IBV infections in chickens.

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.

Development and application of a Saccharomyces cerevisiae-expressed nucleocapsid protein-based enzyme-linked immunosorbent assay for detection of antibodies against infectious bronchitis virus

A Saccharomyces cerevisiae-expressed nucleocapsid (N) polypeptide of the M41 strain of infectious bronchitis virus (IBV) was used as antigen in a recombinant yeast-expressed N protein-based enzyme-linked immunosorbent assay (Y-N-ELISA). The Y-N-ELISA was rapid, sensitive, and specific for detecting chicken serum antibodies to IBV, and it compared favorably with a commercial ELISA.