Protection conferred by live infectious bronchitis vaccine viruses against variant Middle East IS/885/00-like and IS/1494/06-like isolates in commercial broiler chicks

The efficacy of simultaneous successive classic and variant infectious bronchitis virus vaccines versus circulating variant II Egyptian field virus

Background

Being a ubiquitous, highly contagious virus with a continuous mutation and a large number of evolutions worldwide, the infectious bronchitis virus (IBV) continues to wreak problems among Egyptian chickens and generate economic losses. The commonly applied IBV vaccination protocols in broilers include alternatives to classic and/or variant attenuated live virus vaccines.

Aim

The current study targeted to assess the protective efficacy of concurrent and successive Ma5 and 4/91 vaccine strain regimens against the field variant II IBV strain (IBV-EGY-ZU/Ck-127/2021) in chickens.

Methods

Commercial broiler chickens were vaccinated with Ma5 and 4/91 strains simultaneously at 1 and 14 days of age. The evaluation parameters included clinical protection and humoral and early innate immunity aspects in the renal tissues of vaccinated and infected birds.

Results

The vaccine regimen ameliorated the clinical and histopathological lesions against variant II IBV and enhanced body gain as well as succeeded in preventing tracheal shedding and minimizing cloacal shedding of the field virus. The IL-1β mRNA gene expression was evident as early as 24 hours, with highly significant upregulation at 48 hours post vaccination and 24 hours post challenge (PC) in vaccinated birds. Remarkable upregulation was observed in oligoadenylate synthetases (OAS) expression 48 hours PC in vaccinated and unvaccinated infected birds. The vaccinated birds developed a significant antibody titer of 704.0 ± 111.98 at 28 days of age, with a consistent antibody titer increase after the challenge.

Conclusion

Overall, a combination of heterologous protectotype commercial vaccines achieved good protection against the Egyptian variant II IBV strain. This vaccine program could be an effective protocol against the threat posed by IBV viruses circulating in the Egyptian field.

Efficacy of Two Vaccination Strategies against Infectious Bronchitis in Laying Hens

Vaccination remains the leading control method against infectious bronchitis (IB) in poultry despite the frequently observed IB outbreaks in vaccinated flocks. Here, two vaccination regimes were evaluated against challenge with the Massachusetts (Mass) infectious bronchitis virus (IBV) strain that was linked to egg production defects in Western Canada. One vaccination strategy included live attenuated IB vaccines only, and the other used both inactivated and live attenuated IB vaccines. The two immunization programs involved priming with a monovalent live attenuated IB vaccine (Mass serotype) at day-old, followed by intervals of bivalent live attenuated IB vaccines containing the Mass and Connecticut (Conn) serotypes given to the pullets at 2-, 5-, 9-, and 14-week-old. Inactivated IB vaccine (Mass serotype) was administrated to only one group of the vaccinated birds at 14-week-old. At the peak of lay, the hens were challenged with the Mass IBV isolate (15AB-01) via the oculo-nasal route. The efficacy of the vaccines was assessed following the challenge by observing clinical signs, egg production, egg quality parameters, seroconversion, and systemic T-cell subsets (CD4+ and CD8+ cells). Moreover, the viral genome loads in the oropharyngeal (OP) and cloacal (CL) swabs were quantified at predetermined time points. At 14 days post-infection (dpi), all the hens were euthanized, and different tissues were collected for genome load quantification and histopathological examination. Post-challenge, both vaccination regimes showed protection against clinical signs and exhibited significantly higher albumen parameters, higher anti-IBV serum antibodies, and significantly lower levels of IBV genome loads in OP swabs (at 3 and 7 dpi) and trachea and cecal tonsils compared to the mock-vaccinated challenged group. However, only the birds that received live attenuated plus inactivated IB vaccines had significantly lower IBV genome loads in CL swabs at 7 dpi, as well as decreased histopathological lesion scores and IBV genome loads in magnum compared to the mock-vaccinated challenged group, suggesting a slightly better performance for using live attenuated and inactivated IB vaccines in combination. Overall, the present findings show no significant difference in protection between the two vaccination regimes against the Mass IBV challenge in laying hens.

The role of the major viral pathogens in a respiratory disease outbreak of broiler flocks in Eastern Iran

Background

Infectious bronchitis virus (IBV), Newcastle disease virus (NDV), and avian influenza virus (AIV) H9N2 are major viral pathogens in broiler respiratory disease.

Aims

Following a respiratory disease outbreak and economic losses in eastern Iran 2020-2021, we investigated the role of major viral pathogens and the implemented vaccination programs.

Methods

Thirty-six respiratory disease affected broiler flocks in South Khorasan province were sampled, molecularly tested, and coinfections were investigated. The vaccination programs were obtained and the detected IBV were genotyped.

Results

IBV, virulent NDV, and AIV H9N2 were detected in twenty-five, seven, and seven flocks, respectively. IBV+AIV, IBV+NDV, and NDV+AIV coinfections were respectively detected in six, five, and one flocks. Most IBV infected flocks (84%) had been immunized with a live IBV-Mass vaccine. All NDV infected flocks and 14.2% of AIV infected flocks had been vaccinated. IBV genotyping showed a high prevalence of variant 2 (83.3%), followed by Mass-type (12.5%), and Q1-type (4.2%). Variant 2 IB viruses were widely distributed in the province and half of them were mostly similar to the ones that had been detected in northern neighboring province, Khorasan Razavi.

Conclusion

Single infection with variant 2 IBV was a major cause of the respiratory disease outbreak in which use of the Mass vaccine was probably not effective. The high coverage and multiple doses of vaccination against Newcastle disease possibly had reduced the prevalence of NDV. Considering the regional origin of IBV strains, strong biosecurity measures should be implemented and vaccination programs using appropriate vaccine strains should be used.

The efficacy of the prime-boost regimen for heterologous infectious bronchitis vaccines mandates the administration of homologous vaccines

Infectious bronchitis virus (IBV) has been frequently reported in chickens worldwide, including in the Eastern Region of Saudi Arabia (ERS). Several IBV outbreaks were recently reported in chickens despite the massive use of various vaccines. Based on partial sequencing of the S1 gene, at least three genotypes were reported (CK/CH/LDL/97I, IS/720/99, and IS/Variant2/98) in the ERS with no available homologous vaccines. Herein, we tried to evaluate the protection provided by some selected commercial-available vaccines against these three genotypes. We divided the experimental chickens into eight groups. Representative isolates from these genotypes were inoculated into three groups of broiler chickens vaccinated with the H-120 vaccine at the age of 1 day and boosted with the 4/91 vaccine at the age of 14 days (challenged groups). One group of chickens had received the same protocol of IBV vaccines but was kept without infection to serve as a vaccine control group. The three isolates were inoculated into three other similar but unvaccinated groups of broiler chickens (infected groups). Group eight chickens were neither vaccinated nor infected and used as a negative control group. Evaluation of the protection induced by the tested vaccination schedule was assessed by several criteria, including the ability to reduce the severe clinical signs caused by IBV infection, changes in the body temperature of various groups of chickens, the reduction in the magnitude of IBV-induced lesions, and the reduction in the viral loads in tracheas of a different group of chicken. Monitoring the immune status of chickens was also recorded based on the hemagglutination inhibition antibodies in sera of various groups of chickens. Our results show clinical and tracheal protection against IBV/IS/Variant2/98-like and IBV/IS/720/99-like strains. Moderate protection was observed in the IBV/CK/CH/LDL/97I-like pressure. The kidneys of the challenged groups of chickens showed minimal or no gross lesions compared with the infected groups, even in those chickens challenged with the IBV/CK/CH/LDL/97I-like strain. In conclusion, this is the first study to perform the protectotyping of some IBV strains from Saudi Arabia. It demonstrated the proficiency of the investigated vaccination schedule in control of infection of broiler chickens with IBV/IS/Variant2/98 and IBV/IS/720/99 strains. It is highly recommended to introduce the homologous IBV/CK/CH/LDL/97I-based vaccine to the vaccination protocols of chickens in the ERS to match the circulating strains and ensure better protection.

Molecular Characterization Analysis of Prevalent Infectious Bronchitis Virus and Pathogenicity Assessment of Recombination Strain in China

Avian coronavirus infectious bronchitis virus (IBV) is a respiratory pathogen of chickens, resulting in severe economic losses in the poultry industry. This study aimed to monitor and isolate the molecular identity of IBV in broiler flocks with respiratory symptoms in eight provinces of China. In total, 910 samples (oropharyngeal and cloacal mixed swabs) from broiler flocks showed IBV positive rates of 17.6% (160/910) using PCR assay. Phylogenetic analysis of the complete S1 genes of 160 IBV isolates was performed and revealed that QX-type (GI-19), TW-type (GI-7), 4/91-type (GI-13), HN08-type (GI-22),TC07-2-type (GVI-1), and LDT3-type (GI-28) exhibited IBV positive rates of 58.15, 25, 8.12, 1.86, 5.62, and 1.25%. In addition, recombination analyses revealed that the four newly IBV isolates presented different recombination patterns. The CK/CH/JS/YC10-3 isolate likely originated from recombination events between strain YX10 (QX-type) and strain TW2575-98 (TW-type), the pathogenicity of which was assessed, comparing it with strain GZ14 (TW-type) and strain CK/CH/GD/JR07-7 (QX-type). The complete S1 gene data from these isolates indicate that IBV has consistently evolved through genetic recombination or mutation, more likely changing the viral pathogenicity and leading to larger outbreaks in chick populations, in China.

Infectious bronchitis virus infection in chicken: viral load and immune responses in Harderian gland, choanal cleft and turbinate tissues compared to trachea

1. The role of the Harderian gland (HG), choanal cleft (CC) and turbinate in terms of IBV M41 viral load compared to the trachea, and immune (innate, cellular and mucosal) responses were studied in 21-day-old commercial broiler chickens.2. After virulent IBV M41 challenge, the antigen concentration detected either by quantitative RT-PCR or immunohistochemistry peaked at 2-3 days post challenge (dpc) in all tissues. Significant increases of lachrymal IBV-specific IgA and IgY levels were found at 4-5 dpc.3. Gene transcription showed a significant up-regulation of TLR3, MDA5, IL-6, IFN-α and IFN-β, where patterns and magnitude fold-change of mRNA transcription were dependent on the gene and tissue type.4. The results demonstrated active IBV M41 replication in the HG, CC and turbinate, comparable to levels of replication found in the trachea. The data on immune related genes in head-associated tissues provides further understanding on the immunobiology of IBV and offers opportunities to identify their use as quantitative biomarkers in pathogenicity and vaccination-challenge studies.

The inactivated Infectious Bronchitis Virus (IBV) vaccine used as booster in layer hens influences the breadth of protection against challenge with IBV variants

RESEARCH HIGHLIGHTS

IBV vaccination is essential as an aid in protecting laying hens against IBV infectionLive priming is a beneficial part of the IBV vaccination programmeIBV inactivated vaccine improves IBV protectionHeterologous IBV protection is confirmed in laying hens.

Immunogenicity and efficacy of a bivalent vaccine against infectious bronchitis virus

Infectious bronchitis (IB) is a highly contagious viral disease and is responsible for considerable economic losses in the poultry industry, worldwide. To mitigate the IB-associated losses, multiple vaccines are being applied in the sector with variable successes and thus necessitating the development of a potent vaccine to protect against the IB in the poultry. In the present study, we investigated a bivalent live attenuated vaccine consisting of IB virus (IBV) strain H120 (GI-1 lineage) and D274 (GI-12 lineage) to evaluate its protection against heterologous variant of IBV (GI-23 lineage) in chicken. Protection efficacy was evaluated based on the serology, clinical signs, survival rates, tracheal and kidney histopathology and the viral shedding. Results demonstrated that administering live H120 and D274 (named here Classivar®) vaccine in one day-old and 14 days-old provided 100 % protection. We observed a significant increase in the mean antibody titers, reduced virus shedding, and ameliorated histopathology lesions compared to routinely used vaccination regimes. These results revealed that usage of different IBV vaccines combination can successfully ameliorate the clinical outcome and pathology in vaccinated chicks especially after booster vaccination regime using Classivar®. In conclusions, our data indicate that Classivar® vaccine is safe in chicks and may serve as an effective vaccine against the threat posed by commonly circulating IBV strains in the poultry industry.

Factor Influences for Diagnosis and Vaccination of Avian Infectious Bronchitis Virus (Gammacoronavirus) in Chickens

Infectious bronchitis virus (IBV) is a major economic problem in commercial chicken farms with acute multiple-system infection, especially in respiratory and urogenital systems. A live-attenuated and killed vaccine is currently immunized to control IBV infection; however, repeated outbreaks occur in both unvaccinated and vaccinated birds due to the choice of inadequate vaccine candidates and continuous emergence of novel infectious bronchitis (IB) variants and failure of vaccination. However, similar clinical signs were shown in different respiratory diseases that are essential to improving the diagnostic assay to detect IBV infections. Various risk factors involved in the failure of IB vaccination, such as various routes of application of vaccination, the interval between vaccinations, and challenge with various possible immunosuppression of birds are reviewed. The review article also highlights and updates factors affecting the diagnosis of IBV disease in the poultry industry with differential diagnosis to find the nature of infections compared with non-IBV diseases. Therefore, it is essential to monitor the common reasons for failed IBV vaccinations with preventive action, and proper diagnostic facilities for identifying the infective stage, leading to earlier control and reduced economic losses from IBV disease.

The emergence, evolution and spread of infectious bronchitis virus genotype GI-23

Avian infectious bronchitis is a contagious viral disease, caused by avian infectious bronchitis virus (IBV), that leads to severe losses in the poultry industry all over the world. Since the 1950s, IBV has circulated in the Middle East and North Africa, and no tangible evidence has shown any effects of measures taken to control its spread or evolution. Furthermore, new IBV variants are continually discovered. Although several genetic studies on IBV have been conducted, many IBV strains from this region have either been misclassified or remain unclassified. The genotype 23 (GI-23) variant emerged and has prevailed in the Middle East by continuously evolving through inter- and/or intra-genotypic recombination. The GI-23 genotype is currently enzootic throughout Europe and Asia. Although many studies of protection against the circulating strains have been conducted, they have not been standardized according to regulatory requirements. In this review, we provide an overview of the evolution and genetic diversity of IBV genotypes and a genetic classification of IBV strains, with a focus on the GI-23 genotype. The high prevalence of IBV GI-23 strains necessitates the adoption of vaccination schemes using GI-23-based vaccines.

Molecular characterization of isolated infectious bronchitis viruses from affected vaccinated broiler flocks in Syria

Background

Avian Infectious Bronchitis Virus (IBV) is a highly contagious disease that imposes a huge economic burden on the global poultry industry. IBV contains numerous serotypes and variants with incomplete tenuous cross immunological protection. The failure of currently used vaccines to protect against diverse, circulating IBV strains that are specific to a given region poses a major problem for the poultry industry. Thus, there is an urgent need to conduct studies aimed at genotyping field IB viruses. In this study, we have determined the molecular characteristics of circulating IBV by sequencing the S1 gene of viral isolates from affected previously vaccinated broiler flocks suffering from the disease.

Results

Ten isolates propagated in embryonated eggs showed an ability to induce typical IBV lesions after three successive viral passages. We performed a nested RT–PCR assay that targeted the hypervariable region 3 (HVR-3) of the S1 gene, and identified the isolates as IBV through sequence analysis. The IBV isolates showed sequence similarity between the Syrian isolates that vary from 96.20 to 100%, and those being closer to the Variant-2 strain IS/1494/06 (EU780077.2) with 97.5 to 99.4% similarities. However, less nucleotide identity was found with sequences belonging to the used vaccine strains such as H120, Mass5, and 4/91.

Conclusions

This study showed the presence of the Variant-2 strain circulating in Syrian broiler flocks showing signs of IBV disease. Currently, there is no commercial effective vaccine which protects birds against the Variant-2 strain. Continuous monitoring procedures should be taken to control and limit the spread of the IBV Variant-2 strain. This research emphasizes both the importance of epidemiological monitoring in intensive poultry farming for novel pathogens and the use of local isolates as future vaccine targets.

Efficacy of commercial polyvalent avian infectious bronchitis vaccines against Chinese QX-like and TW-like strain via different vaccination strategies

The infectious bronchitis virus (IBV) is an acute and highly contagious disease, which affects chickens of all ages. Vaccination is the most important way to control this disease. Nevertheless, novel variant strains are constantly reported because of the lack of proofreading capabilities of RNA polymerase and high frequency of homologous RNA recombination. Cross-protection studies has demonstrated that the vaccines could provide great protective effects against viruses of same serotype or genotype. However, the protective effect of different commercial vaccines and vaccine combinations against the prevalent IBV strains in China has rarely been studied. Owing to the multiple genotype or serotype IBV strains prevalence in China, the polyvalent vaccines and their composition were used to expanding the protection spectrum of vaccine in practical application. To evaluate the protection of Chinese commercial IBV polyvalent vaccines against prevalent strains (QX-like and TW I-like), an immune challenge test was conducted. Four polyvalent vaccines, containing 4/91, H120, YX10p90, LDT3-A, and 28/86, were combined to form 8 vaccination strategies, almost all of which could provide more than 70% protection effects against challenge with QX-like strain. Particularly, the best protection rate (93%) was generated by administration the polyvalent vaccine C (H120 + 28/86 + 4/91) at 1 D of age and the polyvalent vaccine B (H120 + 4/91 + YX10p90) at 10 D of age. However, all the vaccination strategies in this study cannot provide great protective effects against TW-like strain, and more vaccines should be included in studies to expand the protection spectrum of vaccine. Therefore, for the newly emerging IBV strains, immunization with polyvalent vaccines via different vaccination strategies could be used to control the prevalence of IBV in a short time, whereas developing the homologous vaccines was not always necessary.

Evaluation of inactivated vaccine of the variant 2 (IS-1494 /GI-23) genotype of avian infectious bronchitis

The infectious bronchitis virus (IBV) is the cause of avian infectious bronchitis (IB). IB is one of the most highly contagious diseases, which results in many economic losses in the poultry industry worldwide. The nature of this virus is such that it generates new genotypes continuously. Proper vaccination is the most suitable way of combatting IB. One of the novel genotypes of IBV, which has been circulating in the Middle Eastern countries, is the variant 2 (IS-1494/GI-23) genotype. This study aims to design and produce an autogenous variant 2 vaccines. After isolation and characterization of the Iranian variant 2, the inactivated vaccine was formulated according to the OIE guidelines, and its different aspects (Purity, titration, inactivation, immunization) were evaluated. The designed vaccine passed all of OIE quality control standards. In the assessment process, the protection rate in the groups receiving the variant 2 and commercial vaccines was 67 % and 60 %, respectively. Although the differences were not significant, they indicated better protection, and the viral load in the feces and the kidney of the group receiving the variant 2 vaccine was lower than that in the commercial vaccine. It is suggested that the variant2 strain should be added as one of the local strains to the commercial inactivated vaccines in areas affected by this genotype. The use of this vaccine in layer and breeder flocks can help to protect them against variant 2 during the production phase. Also, the transfer of maternal antibodies to offspring can provide strain-specific immunity for one-day-old chickens.

Effect of IBV D1466 on egg production and egg quality and the effect of heterologous priming to increase the efficacy of an inactivated IBV vaccine

To protect layers, breeders and grandparents against damage by infectious bronchitis virus infections during the laying period, vaccination using live priming followed by a boost with inactivated IB vaccine is commonly used. For many IB variants, homologous live vaccines are not available for priming. Very little is known about the efficacy of priming with heterologous live IB vaccines (or combination of live IB vaccines) to induce broad IB protection in long-living chickens. In this study, the protection levels induced by vaccination programmes with only heterologous live priming by a Massachusetts vaccine and a 4/91 vaccine, only a multivalent inactivated vaccine that contained D1466 antigen and a combination of both, against a D1466 challenge were compared. The infection with infectious bronchitis virus D1466, a genotype II, lineage 1 virus, was able to cause serious damage to the unvaccinated laying hens resulting in respiratory signs, a long-lasting drop in egg production and loss of egg quality. All three vaccination programmes induced significant levels of protection against challenge with a pathogenic D1466 strain. Overall, the vaccination programme using the broad heterologous live priming and the inactivated vaccine provided high protection against the combination of egg drop and loss of egg quality. The results showed that this combination of heterologous live vaccines was able to increase the efficacy of the inactivated infectious bronchitis virus vaccine despite the very low antigenic relationship of both live vaccines with the challenge strain.

Comparative protective immunity provided by live vaccines of Newcastle disease virus or avian metapneumovirus when co-administered alongside classical and variant strains of infectious bronchitis virus in day-old broiler chicks

This study reports on the simultaneous administration of live NDV or aMPV subtype B vaccines alongside two live IBV (Massachusetts-H120 and 793B-CR88) vaccines in day-old maternal-antibody positive commercial broiler chicks. In the first experiment, chicks were divided into four groups; one unvaccinated and three groups vaccinated with live NDV VG/GA-Avinew, live H120 + CR88, or VG/GA-Avinew + H120 + CR88. In the second experiment, live aMPV subtype B vaccine was used in place of NDV. Clinical signs were monitored daily and oropharyngeal swabs were taken at regular intervals for vaccine virus detection. Blood was collected at 21 dpv for serology. 10 chicks from each group were challenged with virulent strains of M41 or QX or aMPV subtype B. For IBV, after 5 days post challenge (dpc), tracheal ciliary protection was assessed. For aMPV, clinical scores were recorded up to 10 dpc. For NDV, haemagglutination inhibition (HI) antibody titres were assayed as an indicator of protective immunity. In both experiments, ciliary protection for IBV vaccinated groups was maintained above 90%. The protection against virulent aMPV challenge was not compromised when aMPV, H120 and CR88 were co-administered. NDV HI mean titres in single and combined NDV-vaccinated groups remained above the protective titre (>3 log2). Both experiments demonstrated that simultaneous administration of live NDV VG/GA-Avinew or aMPV subtype B alongside H120 and CR88 vaccines does not interfere with protection conferred against NDV, IBV or aMPV.

Genotyping of avian infectious bronchitis virus in Iran: Detection of D274 and changing in the genotypes rate

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An updating data about avian infectious bronchitis genotypes circulating in Iran.

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First detection of D274 genotype in Iran.

The coronavirus avian Infectious bronchitis virus (IBV) poses economic threats to poultry farms worldwide, affecting the performance of both meat-type and egg-laying birds. To define the evolution of recent IBVs in Iran, a genetic analysis based on hypervariable nucleotide sequences of S1 gene was carried out. Tracheal swab samples were collected from 170 Broiler flocks during 2017. Ten tracheal swabs from each flock pooled. From a total number of 170 flocks tested, 84.71% found to be positive. Phylogenetic tree analysis revealed the presence of D274 as a first time in Iran. IS/1494/06 was showed to be dominant IBV type circulating in broiler farms with a significantly higher prevalence than other four genotypes. Considering fluctuations in QX-type prevalence in recent years, continuous monitoring is necessary to reduce economic consequences in layer and broiler farms. The findings highlight the importance of using modified vaccination strategies that are adapted to the changing disease scenario.

Infectious bronchitis virus gel vaccination: evaluation of Mass-like (B-48) and 793/B-like (1/96) vaccine kinetics after combined administration at 1 day of age

Infectious bronchitis (IB) control has a strong impact on poultry farming, because of the necessary epidemiological knowledge for planning the best strategy, the optimal strain association, the priming and boosting interventions. Broiler farming is even more problematic given the short and intense productive cycle, which requires an early onset of protection against most of the infectious threats, possibly with limited respiratory post-vaccination reactions that would have a direct impact on the bird health and productivity. For this purpose, gel vaccination has been proposed as a new approach for infectious bronchitis virus (IBV) control and vaccine intake, kinetics and compatibility of combined strains administered by gel have been analyzed in this study. After gel vaccination with single and combined 1/96 and B-48 strains on 4 groups of commercial broilers, a 21-d-long experimental trial has been conducted to monitor the vaccine safety by clinical assessment and vaccine kinetics by strain-specific real-time RT-PCR on choanal cleft swabs. The vaccine strains administered by gel were safe and negligible respiratory signs were detected, even when combined. Vaccine titers were compared among groups and within the same group among a 10-bird pooled sample and 10 swabs from individually sampled birds. 1/96 strain early reached high titers in all animals, while B-48 presence was less constant even though it was detected in almost all birds before the trial end. The individual and pooled sample comparison revealed a partial overestimation of vaccine titers in the pooled samples and the loss of the prevalence data, although the trend portrayed by the pooled swabs closely followed the individual ones.

Including 793/B type avian infectious bronchitis vaccine in 1-day-old chicken increased the protection against QX genotype

Infectious bronchitis virus (IBV) is a highly infectious pathogen, which affects the respiratory tract, reproductive system, and kidney of chickens. Many different genotypes of IBV are recognized which cause different clinical manifestations. According to the antigenic differences, different serotypes of the virus do not cross-protect. Massachusetts serotype induces the best cross-protection against other serotypes. Recently, the IBV QX genotype has been detected in Iran. QX genotype causes permanent damage to the oviduct in layer and breeder flock if it occurs in the early life cycle. In this study, we compared two vaccination program using 793/B type and Massachusetts type vaccine. One-day-old SPF chickens were divided into four groups. Groups 1 and 2 were unvaccinated groups. Group 3 was vaccinated with the H120 vaccine at day 1 and 793/B at day 14 (eye drop), and group 4 was vaccinated with H120+793/B (eye drop) on the first day and 793/B at day 14. Groups 2, 3, and 4 challenged (oculonasal) with QX genotype (10⁴ EID50) at day 35. Five days post challenge, the sample were clollected for ciliostasis test, histopathology, and quantitative real-time RT-PCR from trachea, lung, and kidneys. Results showed that two vaccination programs created more than 80% of protection against challenge virus, but no significant difference was recorded between two programs. Based on our results, it can be concluded that vaccination with two mixed vaccines (H120+793/B) on the first day of the life of a chick does not make any difference in comparison to single vaccine (H120) in reducing of pathological damages and viral load. As long as the second vaccination against IB may not be applied properly in farm situation, applying the mixture of 793/B type vaccine with H120 at day 1 (ocular or spray) may help to increase vaccination program efficacy.

Field Efficacy of an Attenuated Infectious Bronchitis Variant 2 Virus Vaccine in Commercial Broiler Chickens

Egyptian poultry suffer from frequent respiratory disease outbreaks associated with Infectious Bronchitis Virus (IBV) variant 2 strains (Egy/VarII). Different vaccination programs using imported vaccines have failed to protect the flocks from field challenge. Recent studies confirmed a successful protection using homologous strains as live attenuated vaccines. In this study, a newly developed live attenuated IB-VAR2 vaccine representing the GI-23 Middle East IBV lineage was evaluated in day-old commercial broilers in an IBV-endemic area. A commercial broiler flock was vaccinated with the IB-VAR2 vaccine at day-old age followed by IB-H120 at day 16. The vaccinated flock was monitored on a weekly basis till the slaughter age. The health status and growth performance were monitored, and selected viral pathogen real-time RT-PCR (rRT-PCR) detection was conducted on a weekly basis. Finally, the flock was compared to a nearby farm with only the classical IB-H120 vaccination program. Results showed that the IB-VAR2 vaccine was tolerable in day-old broiler chicks. The IBV virus rRT-PCR detection was limited to the trachea as compared to its nephropathogenic parent virus. Respiratory disease problems and high mortalities were reported in the IB-H120-only vaccinated flock. An exposure to a wild-type Egy/VarII strain was confirmed in both flocks as indicated by partial IBV S1 gene sequence. Even though the IB-VAR2-vaccinated flock performance was better than the flock that received only IB-H120, the IBV ELISA (enzyme-linked immunosorbent assay) and log2 Haemagglutination inhibition (HI) antibody mean titers remained high (3128 ± 2713 and ≥9 log2, respectively) until the 28th day of age. The current study demonstrates the safety and effectiveness of IB-VAR2 as a live attenuated vaccine in day-old commercial broilers. Also, the combination of IB-VAR2 and classical IBV vaccines confers a broader protective immune response against IBV in endemic areas.

Efficacy of H120 and Ma5 avian infectious bronchitis vaccines in early challenge against QX strain

Infectious bronchitis (IB) is a highly infectious avian pathogen, which affects the respiratory tract, gut, reproductive system, and kidney of chicks of all ages. Many different serotypes of IB virus (IBV) are recognized which cause different clinical manifestations. According to the antigenic differences, different serotypes of the virus do not cross-protect. Massachusetts serotype induces the best cross-protection against other serotypes. Recently, the IBV QX strain has been detected in Iran. QX strain causes permanent damage to the oviduct if it occurs in the early life cycle and is a significant factor in layer and breeder chicken flocks. In this study, we compare the H120 and Ma5 vaccines’ protection against early challenge with the QX strain in commercial chicks. one-day-old commercial chicks were divided into six groups. Groups 1 and 2 were unvaccinated groups. Groups 3 and 5 were vaccinated with the H120 vaccine (eye drop) and groups 4 and 6 were vaccinated with Ma5 (eye drop) on the 6th day (5 days after vaccination). Groups 2, 3 and 4 challenged (oculonasal) with QX strain (10^⁴ EID50). Ciliostasis test, histopathology, and quantitative real-time RT-PCR were done at 11 days-old of age. Results showed that neither H120 nor Ma5 could induce proper cross-protection against QX early challenge, but the viral load and adverse pathological records in vaccinated chicks were less than that in the non-vaccinated groups. It can be concluded that vaccination on the first day of the life of a chick offers not full protection against the IBV QX strain but reduced the viral load and pathological damages in vaccinated chickens. Applying other forms of vaccination and using different genotypes on one-day-old chicks are suggested.

Heterologous live infectious bronchitis virus vaccination in day-old commercial broiler chicks: clinical signs, ciliary health, immune responses and protection against variant infectious bronchitis viruses

Groups of one-day-old broiler chicks were vaccinated via the oculo-nasal route with different live infectious bronchitis virus (IBV) vaccines: Massachusetts (Mass), 793B, D274 or Arkansas (Ark). Clinical signs and gross lesions were evaluated. Five chicks from each group were humanely killed at intervals and their tracheas collected for ciliary activity assessment and for the detection of CD4+, CD8+ and IgA-bearing B cells by immunohistochemistry (IHC). Blood samples were collected at intervals for the detection of anti-IBV antibodies. At 21 days post-vaccination (dpv), protection conferred by different vaccination regimes against virulent M41, QX and 793B was assessed. All vaccination programmes were able to induce high levels of CD4+, CD8+ and IgA-bearing B cells in the trachea. Significantly higher levels of CD4+ and CD8+ expression were observed in the Mass2 + 793B2-vaccinated group compared to the other groups (subscripts indicate different manufacturers). Protection studies showed that the group of chicks vaccinated with Mass2 + 793B2 produced 92% ciliary protection against QX challenge; compared to 53%, 68% and 73% ciliary protection against the same challenge virus by Mass1 + D274, Mass1 + 793B1 and Mass3 + Ark, respectively. All vaccination programmes produced more than 85% ciliary protection against M41 and 793B challenges. It appears that the variable levels of protection provided by different heterologous live IBV vaccinations are dependent on the levels of local tracheal immunity induced by the respective vaccine combination. The Mass2 + 793B2 group showed the worst clinical signs, higher mortality and severe lesions following vaccination, but had the highest tracheal immune responses and demonstrated the best protection against all three challenge viruses.