Development and efficacy of a novel live-attenuated QX-like nephropathogenic infectious bronchitis virus vaccine in China

Evaluation of different heterologous-homologous vaccine regimens against challenge with GI-23 lineage infectious bronchitis virus

This study assesses different IBV vaccination regimens in broiler chickens using commercially available live attenuated GI-23 (Egyptian-VAR2) and GI-1 (H120) vaccines. Vaccines were administered at 1, 14 days of age, or both. The ciliostasis test, following wild-type VAR2 challenge at 28 days of age, indicated that classic H120+VAR2 at one day old followed by the VAR2 vaccine at 14 days of age provided the highest level of protection (89.58%). Similarly, administering VAR2 at 1 day of age and classic H120 at 14 days of age demonstrated substantial protection (85.42%). Conversely, administering only classic H120 and VAR2 at one day old resulted in the lowest protection level (54.17%). Tracheal virus shedding quantification and assessment of trachea and kidney degenerative changes were significantly lower in vaccinated groups compared to the unvaccinated-challenged group. In conclusion, a carefully planned vaccination regimen based on homologous vaccination offers the most effective clinical protection in broiler chickens.

A New Dual Fluorescence Method for Rapid Detection of Infectious Bronchitis Virus at Constant Temperature

Infectious bronchitis virus (IBV) causes infectious bronchitis in chicken, an acute, highly contagious respiratory infection. Because of genetic mutations and recombination, IBV forms many subtypes, which makes it difficult to treat the disease and apply commercial vaccines. Therefore, to detect IBV in time and stop the virus from spreading, a novel and convenient IBV detection technology based on reverse transcription recombinase-aided amplification (RT-RAA) was established in this study. According to the S1 gene of IBV CH I-V and Mass genotypes and S1 gene of IBV CH VI genotype, a set of optimal primers were designed and selected to establish a real-time dual fluorescence RT-RAA method. The lowest detection line was 10 copies/μL of RNA molecules and the method exhibited no cross-reactivity with avian reticuloendotheliosis virus (REV), infectious bursal disease virus (IBDV), avian leukosis virus (ALV), Newcastle disease virus (NDV), chicken infectious anemia virus (CIAV), infectious laryngotracheitis virus (ILTV), Marek's disease virus (MDV), and H9N2 avian influenza virus (H9N2), demonstrating high specificity. When compared to qPCR detection results, our method achieved a sensitivity of 96.67%, a specificity of 90%, and a Kappa value of 0.87 for the IBV CH I-V and Mass genotypes, and achieved a sensitivity of 100%, a specificity of 97.73%, and a Kappa value of 0.91 for the IBV CH VI genotype.

Deciphering the Genetic Variation: A Comparative Analysis of Parental and Attenuated Strains of the QXL87 Vaccine for Infectious Bronchitis

The QXL87 live attenuated vaccine strain for infectious bronchitis represents the first approved QX type (GI-19 lineage) vaccine in China. This strain was derived from the parental strain CK/CH/JS/2010/12 through continuous passage in SPF chicken embryos. To elucidate the molecular mechanism behind its attenuation, whole-genome sequencing was conducted on both the parental and attenuated strains. Analysis revealed 145 nucleotide mutations in the attenuated strain, leading to 48 amino acid mutations in various proteins, including Nsp2 (26), Nsp3 (14), Nsp4 (1), S (4), 3a (1), E (1), and N (1). Additionally, a frameshift mutation caused by a single base insertion in the ORFX resulted in a six-amino-acid extension. Subsequent comparison of post-translational modification sites, protein structure, and protein-protein binding sites between the parental and attenuated strains identified three potential virulence genes: Nsp2, Nsp3, and S. The amino acid mutations in these proteins not only altered their conformation but also affected the distribution of post-translational modification sites and protein-protein interaction sites. Furthermore, three potential functional mutation sites-P106S, A352T, and L472F, all located in the Nsp2 protein-were identified through PROVEAN, PolyPhen, and I-Mutant. Overall, our findings suggest that Nsp2, Nsp3, and S proteins may play a role in modulating IBV pathogenicity, with a particular focus on the significance of the Nsp2 protein. This study contributes to our understanding of the molecular mechanisms underlying IBV attenuation and holds promise for the development of safer live attenuated IBV vaccines using reverse genetic approaches.

Prevalence, Genotype Diversity, and Distinct Pathogenicity of 205 Gammacoronavirus Infectious Bronchitis Virus Isolates in China during 2019-2023

Gammacoronavirus infectious bronchitis virus (IBV) causes a highly contagious disease in chickens and seriously endangers the poultry industry. The emergence and co-circulation of diverse IBV serotypes and genotypes with distinct pathogenicity worldwide pose a serious challenge to the development of effective intervention measures. In this study, we report the epidemic trends of IBV in China from 2019 to 2023 and a comparative analysis on the antigenic characteristics and pathogenicity of isolates among major prevalent lineages. Phylogenetic and recombination analyses based on the nucleotide sequences of the spike (S) 1 gene clustered a total of 205 isolates into twelve distinct lineages, with GI-19 as a predominant lineage (61.77 ± 4.56%) exhibiting an overall increasing trend over the past five years, and demonstrated that a majority of the variants were derived from gene recombination events. Further characterization of the growth and pathogenic properties of six representative isolates from different lineages classified four out of the six isolates as nephropathogenic types with mortality rates in one-day-old SPF chickens varying from 20-60%, one as a respiratory type with weak virulence, and one as a naturally occurring avirulent strain. Taken together, our findings illuminate the epidemic trends, prevalence, recombination, and pathogenicity of current IBV strains in China, providing key information for further strengthening the surveillance and pathogenicity studies of IBV.

Molecular Prevalence Study of QX-like Infectious Bronchitis Virus in Japan from 2016 to 2023

Infectious bronchitis is an acute and highly contagious disease in chickens caused by the infectious bronchitis virus (IBV), which has caused significant economic losses to the poultry industry worldwide. The antigenic variant, the QX-like genotype (GI-19 lineage), has been currently reported in epidemics in East Asia, Southeast Asia, the Middle East, Europe, and Africa. We first reported an epidemic of Japanese QX-like IBVs genetically related to Chinese and South Korean strains in the Kyushu region of Japan in 2020. However, because their nationwide prevalence was unknown, we performed a nationwide survey. The testing of 419 reverse transcription (RT)-PCR-positive samples (376 layers and 43 broilers) of IBV field strains between April 2016 and March 2022 detected two QX-like IBVs in 2019 and 2021 broiler samples from one region. A survey of fecal samples collected from 122-layer farms nationwide between November 2022 and January 2023 detected QX-like IBV genes from seven farms in various regions. Phylogenetic tree analysis on the basis of the S1 gene showed that all QX-like IBVs detected in Japan were genetically related to recent Chinese and South Korean strains. A new RT-PCR assay was developed to distinguish between QX-like IBV and other IBV variants prevalent in Japan, whose results were consistent with those of previously reported identification methods. These results suggest that QX-like IBV is rapidly spreading in Japan and that countermeasures are necessary.

Insights on genetic characterization and pathogenesis of a GI-19 (QX-like) infectious bronchitis virus isolated in China

Infectious bronchitis virus (IBV) causes respiratory diseases in chickens, incurring great losses to the poultry industry worldwide. In this study, we isolated an IBV strain, designated as AH-2020, from the chickens vaccinated with H120 and 4/91 in Anhui, China. The sequence homology analysis based on the S1 gene revealed that AH-2020 shares low similarities with the 3 vaccine strains, namely, H120, LDT3-A, and 4/91 (78.19, 80.84, and 81.6%, respectively). Phylogenetic analysis based on the S1 gene revealed that AH-2020 clustered with the GI-19 type. Furthermore, protein modeling revealed that the mutations in the amino acids in AH-2020 were mainly located in the N-terminal domain of S1 (S1-NTD), and the pattern of deletion and insertion mutations in the S1 protein may have influenced the structural changes on the surface of S1. Further, approximately 7-day-old SPF chickens were inoculated with AH-2020 at 10^6.0 EID₅₀. These chickens exhibited clinical signs of the infection such as listlessness, huddling, and head-shaking, accompanied by depression and 40% mortality. Serum antibody test demonstrated that in response to the AH-2020 infection, the antibody level increased the fastest at 7 dpi, with virus shedding rate of cloaca being 100% at 14 dpi. The viral titer in various tissues was detected using hematoxylin and eosin staining and immunohistochemistry, which revealed that AH-2020 infection can damage the kidney, trachea, lung, cecal tonsil, and bursa of Fabricius. Our study provided evidence that the GI-19-type IBV is undergoing more complex mutations, and effective measures are urgently needed to prevent the spread of these variant strains.

Radix Isatidis polysaccharide (RIP) resists the infection of QX-type infectious bronchitis virus via the MDA5/TLR3/IRF7 signaling pathway

Although vaccines play a major role in the prevention of infectious bronchitis (IB), Anti-IB drugs still have great potential in poultry production. Radix Isatidis polysaccharide (RIP) is a crude extract of Banlangen with antioxidant, antibacterial, antiviral, and multiple immunomodulatory functions. The aim of this study was to explore the innate immune mechanisms responsible for RIP-mediated alleviation of infectious bronchitis virus (IBV)-induced kidney lesions in chickens. Specific-pathogen-free (SPF) chicken and chicken embryo kidney (CEK) cells cultures were pretreated with RIP and then infected with the QX-type IBV strain, Sczy3. Morbidity, mortality, and tissue mean lesion scores were calculated for IBV-infected chickens, and the viral loads, inflammatory factor gene mRNA expression levels, and innate immune pathway gene mRNA expression levels in infected chickens and CEK cell cultures were determined. The results show that RIP could alleviate IBV-induced kidney damage, decrease CEK cells susceptibility to IBV infection, and reduce viral loads. Additionally, RIP reduced the mRNA expression levels of the inflammatory factors IL-6, IL-8, and IL-1β by decreasing the mRNA expression level of NF-κB. Conversely, the expression levels of MDA5, TLR3, STING, Myd88, IRF7, and IFN-β were increased, indicating that RIP conferred resistance to QX-type IBV infection via the MDA5, TLR3, IRF7 signaling pathway. These results provide a reference for both further research into the antiviral mechanisms of RIP and the development of preventative and therapeutic drugs for IB.

Establishment and Cross-Protection Efficacy of a Recombinant Avian Gammacoronavirus Infectious Bronchitis Virus Harboring a Chimeric S1 Subunit

Infectious bronchitis virus (IBV) is a gammacoronavirus that causes a highly contagious disease in chickens and seriously endangers the poultry industry. A diversity of serotypes and genotypes of IBV have been identified worldwide, and the currently available vaccines do not cross-protect. In the present study, an efficient reverse genetics technology based on Beaudette-p65 has been used to construct a recombinant IBV, rIBV-Beaudette-KC(S1), by replacing the nucleotides 21,704–22,411 with the corresponding sequence from an isolate of QX-like genotype KC strain. Continuous passage of this recombinant virus in chicken embryos resulted in the accumulation of two point mutations (G21556C and C22077T) in the S1 region. Further studies showed that the T248S (G21556C) substitution may be essential for the adaptation of the recombinant virus to cell culture. Immunization of chicks with the recombinant IBV elicited strong antibody responses and showed high cross-protection against challenges with virulent M41 and a QX-like genotype IBV. This study reveals the potential of developing rIBV-Beau-KC(S1) as a cell-based vaccine with a broad protective immunity against two different genotypes of IBV.

The Efficacy of a Live Attenuated TW I-Type Infectious Bronchitis Virus Vaccine Candidate

Infectious bronchitis (IB) is a highly contagious avian disease caused by infection with infectious bronchitis virus (IBV), which seriously affects the development of the global poultry industry. The distribution of TW I-type IBV in China has increased in recent years, becoming a widespread genotype. We previously isolated a TW I-type IBV strain termed CK/CH/GD/GZ14 in 2014, but its pathogenicity and possibility for vaccine development were not explored. Therefore, this research aimed to develop a live-attenuated virus vaccine based on the CK/CH/GD/GZ14 strain. The wild type IBV CK/CH/GD/GZ14 strain was serially passaged in SPF embryos for 145 generations. The morbidity and mortality rate of wild-type strain in 14 day-old chickens is 100% and 80% respectively, while the morbidity rate in the attenuated strain was 20% in the 95th and 105th generations and there was no death. Histopathological observations showed that the pathogenicity of the 95th and 105th generations in chickens was significantly weakened. Further challenge experiments confirmed that the attenuated CK/CH/GD/GZ14 strain in the 95th and 105th generations could resist CK/CH/GD/GZ14 (5th generation) infection and the protection rate was 80%. Tracheal cilia stagnation, virus shedding, and viral load experiments confirmed that the 95th and 105th generations provide good immune protection in chickens, and the immunogenicity of the 105th generation is better than that of the 95th generation. These data suggest that the attenuated CK/CH/GD/GZ14 strain in the 105th generation may be applied as a vaccine candidate against TW I-type IBV.

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.

Chlorogenic acid is a positive regulator of MDA5, TLR7 and NF-κB signaling pathways mediated antiviral responses against Gammacoronavirus infection

Chlorogenic acid (CGA) is a phenolic compound that has been well studied for its antiviral, anti-inflammatory and immune stimulating properties. This research was aimed to focus on the antiviral properties of CGA on infectious bronchitis virus (IBV) in vivo and in vitro for the very first time. The outcome of in vitro experiments validated that, out of five previously reported antiviral components, CGA significantly reduced the relative mRNA expression of IBV-N in CEK cells. At high concentration (400 mg/kg), CGA supplementation reduced IBV-N mRNA expression levels and ameliorated the injury in trachea and lungs. The mRNA expression levels of IL-6, IL-1β, IL-12, and NF-κB were considerably turned down, but IL-22 and IL-10 were enhanced in trachea. However, CGA-H treatment had considerably increased the expression levels of MDA5, MAVS, TLR7, MyD88, IRF7, IFN-β and IFN-α both in trachea and lungs. Moreover, CGA-H notably induced the CD3+, CD3+ CD4+ and CD4+/CD8+ proliferation and significantly increased the IgA, IgG, and IgM levels in the serum. In conclusion, these results showed that at high concentration CGA is a strong anti-IBV compound that can effectively regulate the innate immunity through MDA5, TLR7 and NF-κB signaling pathways and have the potential to induce the cell mediated and humoral immune response in IBV infected chickens.

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.

Towards Improved Use of Vaccination in the Control of Infectious Bronchitis and Newcastle Disease in Poultry: Understanding the Immunological Mechanisms

Infectious bronchitis (IB) and Newcastle disease (ND) are two important diseases of poultry and have remained a threat to the development of the poultry industry in many parts of the world. The immunology of avian has been well studied and numerous vaccines have been developed against the two viruses. Most of these vaccines are either inactivated vaccines or live attenuated vaccines. Inactivated vaccines induce weak cellular immune responses and require priming with live or other types of vaccines. Advanced technology has been used to produce several types of vaccines that can initiate prime immune responses. However, as a result of rapid genetic variations, the control of these two viral infections through vaccination has remained a challenge. Using various strategies such as combination of live attenuated and inactivated vaccines, development of IB/ND vaccines, use of DNA vaccines and transgenic plant vaccines, the problem is being surmounted. It is hoped that with increasing understanding of the immunological mechanisms in birds that are used in fighting these viruses, a more successful control of the diseases will be achieved. This will go a long way in contributing to global food security and the economic development of many developing countries, given the role of poultry in the attainment of these goals.

Phylogenetic analysis of infectious bronchitis virus circulating in southern China in 2016-2017 and evaluation of an attenuated strain as a vaccine candidate

Avian infectious bronchitis (IB) is a highly contagious viral respiratory disease, caused by infectious bronchitis virus (IBV), that poses an important economic threat to the poultry industry. In recent years, genotypes GI-7, GI-13, and GI-19 have been the most prevalent IBV strains in China. However, in this study, we found that most IBV strains from southern China in 2016-2017 belonged to genotype GVI-1. This genotype, for which there is no vaccine, has been reported sporadically in the region. The GDTS13 strain, which caused severe IB outbreaks on the farms where it was isolated, was evaluated as a candidate vaccine strain. GDTS13 was serially passaged in specific-pathogen-free embryonated chicken eggs for 100 generations to produce GDTS13-F100. Safety testing indicated that GDTS13-F100 had no pathogenic effect on chickens. Additionally, GDTS13-F100 showed an excellent protective effect against GDTS13, with no clinical signs or virus shedding observed in immunized chickens challenged with the parent strain. These findings indicate that GVI-1 has become the most prevalent IBV genotype in southern China and that GDTS13-F100 may serve as an attenuated vaccine to protect against infection with this genotype.

Characterization of S1 gene sequence variations of attenuated QX-like and variant infectious bronchitis virus strains and the pathogenicity of the viruses in specific-pathogen-free chickens

Besides the vaccine strains, the Malaysian variant (MV) and QX-like are the predominant IBVs detected on commercial poultry farms. These two virus strains are distinct based on genomic and pathogenicity studies. In this study, we determined the sequence of the S1 gene and compared the pathogenicity of serial passage 70 (P70) of Malaysian QX-like (QX/P70) and MV (MV/P70) strains with that of their respective wild-type viruses. The nucleotide and amino acid sequences of the complete S1 genes of QX/P70 and MV/P70 showed 1.4 to 1.6% and 3.0 to 3.3% variation, respectively, when compared to the wild-type virus. Most of the mutations were insertions and substitutions in the hypervariable regions (HVRs), primarily in HVR 3. Furthermore, selection pressure analysis showed that both viruses are under purifying selection. A pathogenicity study in specific-pathogen-free (SPF) chickens showed a reduction in respiratory and kidney lesions in chickens inoculated with MV/P70, but not with QX/P70, when compared to the respective wild-type viruses. However, MV/P70 is still pathogenic and can cause ciliary damage. In conclusion, the MV IBV strain is more responsive than the QX-like IBV strain following the attenuation process used for the development of a live attenuated IBV vaccine.

Protective effects of hypericin against infectious bronchitis virus induced apoptosis and reactive oxygen species in chicken embryo kidney cells

Avian infectious bronchitis virus (IBV), a coronavirus, causes infectious bronchitis leading to enormous economic loss in the poultry industry worldwide. Hypericin (HY) is an excellent compound that has been investigated in antiviral, antineoplastic, and antidepressant. To investigate the inhibition effect of HY on IBV infection in chicken embryo kidney (CEK) cells, 3 different experimental designs: pre-treatment of cells prior to IBV infection, direct treatment of IBV-infected cells, and pre-treatment of IBV prior to cell infection were used. Quantitative real-time PCR (qRT-PCR), immunofluorescence assay (IFA), flow cytometry, and fluorescence microscopy were performed and virus titer was determined by TCID50. The results revealed that HY had a good anti-IBV effect when HY directly treated the IBV-infected cells, and virus infectivity decreased in a dose-dependent manner. Furthermore, HY inhibited IBV-induced apoptosis in CEK cells, and significantly reduced the mRNA expression levels of Fas, FasL, JNK, Bax, Caspase 3, and Caspase 8, and significantly increased Bcl-2 mRNA expression level in CEK cells. In addition, HY treatment could decrease IBV-induced reactive oxygen species (ROS) generation in CEK cells. These results suggested that HY showed potential antiviral activities against IBV infection involving the inhibition of apoptosis and ROS generation in CEK cells.

Genetic sequence changes related to the attenuation of avian infectious bronchitis virus strain TW2575/98

The attenuated avian infectious bronchitis virus (IBV), derived from a wild strain (TW2575/98w) in chicken embryos after 75 passages, is designed as a commercial vaccine strain (TW2575/98vac) to control the disease in Taiwan. The differences in viral infectivity, replication efficiency, and genome sequences between TW2575/98w and TW2575/98vac were determined and compared. TW2575/98vac caused earlier death of chicken embryos and had higher viral replication efficiency. Thirty amino acid substitutions resulting from 44 mutated nucleotides in the viral genome were found in TW2575/98vac. All of the molecular variations lead to attenuation, found in TW2575/98, were not observed consistently in the other IBVs (TW2296/95, Ark/Ark-DPI/81, the Massachusetts strain, GA98/CWL0470/98, and CK/CH/LDL/97I) and vice versa. After further comparisons and evaluations from three aspects: (1) longitudinal analysis on the timing of variations appeared in specific homologous strain passages, (2) horizontal evaluations with the amino acid changes between wild and vaccine strains among the other 5 IBVs, and (3) inspection on alterations in the chemical characteristics of substituted amino acid residues in viral proteins, four amino acid substitutions [V342D in p87, S1493P and P2025S in HD1, as well as F2308Y in HD1(P41)] were selected as highly possible candidates for successful TW2575/98w attenuation. Our findings imply that molecular variations, which contribute to the successful attenuation of different IBVs, are diverse and not restricted to a fixed pattern or specific amino acid substitutions in viral proteins. In addition, four amino acid changes within the replicase gene-encoded proteins might be associated with TW2575/98 virus virulence.

Recombinant infectious bronchitis coronavirus H120 with the spike protein S1 gene of the nephropathogenic IBYZ strain remains attenuated but induces protective immunity

Infectious bronchitis (IB) is a highly infectious viral disease responsible for major economic losses in the poultry industry. A reverse genetic vaccine is a safe, rapid, and effective method of achieving IB prevention and control. In this study, we constructed the recombinant strain, rH120-S1/YZ, using a reverse genetic system, based on the backbone of the H120 vaccine strain, with the S1 gene replaced with that of the QX-like nephropathogenic strain, ck/CH/IBYZ/2011, isolated in China. The results of dwarf chicken embryos, growth kinetics, and viral titration in the embryos demonstrated that the biological characteristics of the recombinant virus remained unchanged. Like the rH120-infected group and in contrast to the rIBYZ-infected group, no mortality, clinical signs, or lesions were observed in the lungs or kidneys of young chickens inoculated with rH120-S1/YZ. The viral loads in various tissues, cloacal, and oral swabs was lower in most types of samples, indicating that the rH120-S1/YZ strain was highly safe in chicks. Compared to rH120 vaccination group, when the efficacy of this strain was evaluated against the QX-like IBV strain, better protection, with 100% survival rate and no disease symptom or gross lesion was observed in the chickens vaccinated with rH120-S1/YZ. Increased levels of IBV-specific antibodies were detected in the serum of the rH120-S1/YZ-vaccinated animals 14 days post-vaccination. Collectively, our results suggest that the recombinant strain, rH120-S1/YZ, may represent a promising vaccine candidate against QX-like IBVs.

A novel low virulent respiratory infectious bronchitis virus originating from the recombination of QX, TW and 4/91 genotype strains in China

In China, variants of infectious bronchitis virus (IBV) evolve continually and diverse recombinant strains have been reported. Here, an IBV strain, designated as ck/CH/LJX/2017/07 (referred as JX17) was isolated from chicken vaccinated with H120 and 4/91 in Jiangxi, China, in 2017. Sequence analysis reveals of the S1 gene of JX17 the highest nucleotide identity of 98.15% with that of GI-7 genotype TW2575/98 strain. Furthermore, whole genome analysis among JX17 and other 18 IBV strains demonstrates that JX17 has the highest nucleotide identity of 95.94% with GI-19 genotype YX10 strain. Among all genes of JX17 except the S1 gene, the N gene and 3' UTR have the highest identity to GI-13 genotype 4/91 strain and the rest genes are the most identical to GI-19 genotype YX10 strain. Analyzed by the RDP and SimPlot, the recombination of JX17 strain was shown to occur in regions which include 5'-terminal S1 gene (20,344 to 22,447 nt), most N gene and 3' UTR (26,163 to 27,648 nt). The pathogenicity study shows that JX17 is a natural low virulent IBV variant which caused respiratory symptoms but no death. Taken together, these results indicate that IBV strains continue to evolve through genetic recombination and three prevalent genotypes in China including QX, TW and 4/91 have started to recombine.

Molecular epidemiology of infectious bronchitis virus and avian metapneumovirus in Greece

Respiratory diseases like infectious bronchitis virus (IBV) and avian metapneumovirus (aMPV) have been held accountable for major losses for poultry production. Nevertheless, scarce information was present dealing with the prevalence and molecular epidemiology of these infections in Greece and the efficacy of currently applied control strategies. To fill this gap, a specific epidemiological study was designed. A total of 106 broiler and layer farms, including 10 backyard and 96 commercial flocks, were sampled between March 2016 and May 2017, and the obtained tracheal swabs were tested for IBV and aMPV using RT-PCR based techniques followed by sequencing. For each farm, data regarding production type, flock features, clinical signs, and vaccination program were also recorded. Different associations between vaccination protocol, production type, animal category, birds density, age, presence of clinical signs, and IBV and/or aMPV infection were tested. Both IBV and aMPV field strain prevalence were proven high, approximately 20 and 30%, respectively, being the GI-19 lineage (14 out of 19; 73.6%) and B subtype (30 out of 30; 100%), the most commonly detected IBV and aMPV genetic types. Infection with IBV field strains was significantly associated with clinical sign presence (odds ratio = 8.55 [95CI = 2.17–42.90]). Remarkably, only the vaccination protocol involving a double vaccination at 1 D of age was proven protective against IBV-induced symptomatology, with the odds of developing disease being 4.14 [95CI = 1.34–14.51] times lower.

No association was demonstrated between aMPV infection and clinical outbreaks or between aMPV and IBV detection, suggesting the marginal role of the former pathogen in poultry farming.

Globally, the present study provides the first detailed investigation of the epidemiological scenario of 2 viruses traditionally considered of pivotal relevance in poultry farming and demonstrates that remarkable benefits could be obtained with just minor adjustments in vaccination protocols.

Pathogenicity of a QX-like avian infectious bronchitis virus isolated in China

Avian infectious bronchitis is a serious and highly contagious disease caused by infectious bronchitis virus (IBV). We isolated a highly virulent IBV strain (CK/CH/JS/TAHY) from kidneys of diseased chickens. Phylogenetic analysis based on the S1 gene revealed that CK/CH/JS/TAHY clustered with the QX-like type. The S1 gene has 1,620 nucleotides and encoded a polypeptide of 540 amino acids with typical coronavirus cleavage recognition sites of HRRR. About 1-day-old specific pathogen-free White Leghorn chickens inoculated with CK/CH/JS/TAHY at 105.5 EID50 exhibited clinical signs including coughing, sneezing, nasal discharge, and tracheal vocalization accompanied by depression with 84% mortality and 100% morbidity. The kidneys of dead birds were swollen and pale and exhibited severe urate deposition. Histopathological examination revealed kidney hemorrhages, multifocal necrosis of the renal tubules and trachea with cilia loss, sloughing of epithelial cells, and edema of the lamina propria. IBV-specific antibodies appeared at 10 D post-infection. Chickens vaccinated with a CK/CH/JS/TAHY oil-emulsion vaccine showed 26.7% morbidity and 3% mortality indicating a protective effect. In conclusion, the IBV strain is a virulent avian IBV and that exhibited severe pathogenicity in chickens and is a vaccine candidate to prevent infection by Chinese QX-like nephropathogenic IBV strains.

Antiviral Activity Against Infectious Bronchitis Virus and Bioactive Components of Hypericum perforatum L

Hypericum perforatum L., also known as Saint John’s Wort, has been well studied for its chemical composition and pharmacological activity. In this study, the antiviral activities of H. perforatum on infectious bronchitis virus (IBV) were evaluated in vitro and in vivo for the first time. The results of in vitro experiments confirmed that the antiviral component of H. perforatum was ethyl acetate extraction section (HPE), and results showed that treatment with HPE significantly reduced the relative messenger ribonucleic acid (mRNA) expression and virus titer of IBV, and reduced positive green immunofluorescence signal of IBV in chicken embryo kidney (CEK) cells. HPE treatment at doses of 480–120 mg/kg for 5 days, reduced IBV induced injury in the trachea and kidney, moreover, reduced the mRNA expression level of IBV in the trachea and kidney in vivo. The mRNA expression levels of IL-6, tumor necrosis factor alpha (TNF-α), and nuclear factor kappa beta (NF-κB) significantly decreased, but melanoma differentiation-associated protein 5 (MDA5), mitochondrial antiviral signaling gene, interferon alpha (IFN-α), and interferon beta (IFN-β) mRNA levels significantly increased in vitro and in vivo. Our findings demonstrated that HPE had significant anti-IBV effects in vitro and in vivo, respectively. In addition, it is possible owing to up-regulate mRNA expression of type I interferon through the MDA5 signaling pathway and down-regulate mRNA expression of IL-6 and TNF-α via the NF-κB signaling pathway. Moreover, the mainly active compositions of HPE analyzed by high-performance liquid chromatography/electrospray ionization–mass spectroscopy (ESI-MS) are hyperoside, quercitrin, quercetin, pseudohypericin, and hypericin, and a combination of these compounds could mediate the antiviral activities. This might accelerate our understanding of the antiviral effect of H. perforatum and provide new insights into the development of effective therapeutic strategies.

Protective Efficacy of Different Live Attenuated Infectious Bronchitis Virus Vaccination Regimes Against Challenge With IBV Variant-2 Circulating in the Middle East

Six vaccination regimes using classical (Mass-type) and variant (IB-VAR2 and IB-793B) live vaccines were evaluated against Middle Eastern variant-2 infectious bronchitis virus challenge. Six groups of SPF chicks (30 birds/group) were vaccinated using prime-boost regimes at day-1 and day-14 using; IB-M41:IB-VAR2, IB-VAR2:IB-VAR2, IB-VAR2:IB-M41, IB-Ma5:IB-793B, IB-793B:IB-793B, and IB-793B:IB-Ma5, respectively. Ciliostasis and lesion scores were evaluated at day-5 after each vaccination. Birds were challenged intranasally at 14-day post 2nd vaccination using 10⁵EID₅₀/0.1 ml/bird of wild-type IBV (Eg/1212B/2012). At 3, 5, and 7-day post challenge (DPC) virus shedding was monitored by real-time RT-PCR. Five chicks/group were euthanized at 7DPC for ciliostasis and lesion scoring and histopathology was conducted on 3 chicks/group. Seroconversion was evaluated at 14 DPC. All groups primed with the 793B vaccine showed relatively higher ciliostasis scores compared to other groups. The IB-VAR2 vaccinated groups showed the highest protection rates (80–100%) and high protection score (67.6–73.2%) compared to the 793B vaccine groups (50–60%). The virus shedding was significantly reduced at 3 and 5DPC in groups received the IBV-VAR2 (prime or booster) compared to those received the 793B vaccine. In conclusion, the homologous IBV-VAR2 vaccine showed superior results compared to 793B or Mass-type vaccines confirming the importance of IBV vaccine seed homology to the circulating IBV strains.

Safety and efficacy of attenuated classic and variant 2 infectious bronchitis virus candidate vaccines

Vaccination programs against infectious bronchitis virus (IBV) in Egypt depend on both classical and/or imported variant IBV strain vaccines. However, many IBV outbreaks associated with respiratory distress, nephropathy, and high mortalities were attributed to the circulation of both classical and new nephropathogenic IBV variant 2 strains. In the present study, we report the development of attenuated IBV candidate vaccines using the classic IBV strains (IBM41 and IB2) and a nephropathogenic strain (IBvar2). The wild-type (WT) viruses were attenuated through serial passages in embryonated specific pathogen free (SPF) chicken eggs. Virulence of the attenuated viruses was then tested via the ocular route inoculation and the in vivo back passage in day-old SPF chickens. Efficacy against homologous challenge was investigated also in day-old SPF chickens. Results showed that the viruses were successfully adapted to the embryo by the 100th (IBM41 and IB2) and 110th passages (IBvar2). The attenuated viruses were safe and showed no change of virulence in day-old SPF chickens up to the 10th back passages. The efficacy experiment showed that the attenuated vaccines showed 90 to 100% protection against the homologous challenge based on ciliostasis score and protection percent. The att-IBM41 and att-IB2 vaccines were able to reduce the shedding of the challenge at 3 days post-infection (DPI) and no virus shedding was detected in both vaccinated groups by 5 DPI. In the att-IBvar2 vaccinated birds, only 20% of vaccinated birds shed the challenge virus with low titers (102.10±0.3 EID50/mL) at 3 DPI. In conclusion, the attenuated strains IBM41, IB2, and IBvar2 are efficient vaccine candidates against currently circulating classic and variant IB viruses, respectively. Further studies to evaluate the field efficacy and combining these attenuated IBV strains to induce a wider protection against heterologous IBV challenge are suggested.

Pathobiological and Genomic Characterization of a Cold-Adapted Infectious Bronchitis Virus (BP-caKII)

We established a cold-adapted infectious bronchitis virus (BP-caKII) by passaging a field virus through specific pathogen-free embryonated eggs 20 times at 32 °C. We characterized its growth kinetics and pathogenicity in embryonated eggs, and its tropism and persistence in different tissues from chickens; then, we evaluated pathogenicity by using a new premature reproductive tract pathogenicity model. Furthermore, we determined the complete genomic sequence of BP-caKII to understand the genetic changes related to cold adaptation. According to our results, BP-caKII clustered with the KII genotype viruses K2 and KM91, and showed less pathogenicity than K2, a live attenuated vaccine strain. BP-caKII showed delayed viremia, resulting in its delayed dissemination to the kidneys and cecal tonsils compared to K2 and KM91, the latter of which is a pathogenic field strain. A comparative genomics study revealed similar nucleotide sequences between BP-caKII, K2 and KM91 but clearly showed different mutations among them. BP-caKII shared several mutations with K2 (nsp13, 14, 15 and 16) following embryo adaptation but acquired multiple additional mutations in nonstructural proteins (nsp3, 4 and 12), spike proteins and nucleocapsid proteins following cold adaptation. Thus, the establishment of BP-caKII and the identified mutations in this study may provide insight into the genetic background of embryo and cold adaptations, and the attenuation of coronaviruses.

Effects of dietary yeast nucleotides supplementation on intestinal barrier function, intestinal microbiota, and humoral immunity in specific pathogen-free chickens

Yeast nucleotides are a fine functional additive in human and animals. The effects of dietary yeast nucleotides supplementation on intestinal development, expression of intestinal barrier-related genes, intestinal microbiota, and infectious bronchitis virus (IBV) antibody titer of specific pathogen-free (SPF) chickens were investigated. A total of 60 1-d-old chickens were divided into 4 groups, each of which included 3 replicates of 5 chickens. Group 1 served as a control that was fed a basal diet. Groups 2 to 4 were fed the basal diet supplemented with 0.1%, 0.3% and 0.5% yeast nucleotides, respectively. All chickens were inoculated intranasally with inactivated IBV vaccine at day 1 and day 10. At day 17, the intestinal development, expression of intestinal barrier-related genes and microbiota were evaluated. There was a significant increased ileal villus height and villus height to crypt depth ratio in group 2 (P < 0.05). Moreover, group 4 exhibited higher expression of zonula occludens-1 (ZO-1) and Occludin gene in ileum (P < 0.05), whereas groups 2 and 3 exhibited higher expression of Mucin 2 (MUC2) and trefoil factor 2 (TFF2) gene (P < 0.05), group 2 showed lower expression of IFN-α gene (P < 0.05). Dietary yeast nucleotides increased intestinal bacterial diversity (P < 0.05), and the abundance of Lactobacillus (P < 0.05). At day 10, 17, 24, 31, 38, and 45, the serum IBV antibody titers were tested. Group 2 exhibited higher IBV antibody titer at day 17 (P < 0.05), furthermore, groups 2 to 4 reached the effective levels 1 wk earlier than control group. In conclusion, dietary yeast nucleotides supplementation can help birds to mount a faster and stronger antibody response to IBV vaccine. In addition, dietary yeast nucleotides supplementation can also promote the intestinal development and barrier-related genes expression, and diversity and richness of intestinal microbiota.

Molecular characteristic and pathogenicity analysis of a virulent recombinant avain infectious bronchitis virus isolated in China

A virulent infectious bronchitis virus (IBV), designated as CK/CH/GD/QY16 (referred as QY16), was isolated from a diseased chicken farm in Guangdong province, China, in 2016. The complete genome of the strain was sequenced and analyzed. The results show that the genome of QY16 consists of 27,670 nucleotides, excluding poly (A) tail, and that its genome organization is 5’ UTR-1a-1b-S-3a-3b-E-M-4b-4c-5a-5b-N-6b-3’ UTR-poly (A) tail. Sequence comparison among QY16 and other IBV strains was conducted and its results demonstrate that the S1 gene of QY16 has the highest nucleotide sequence identity with that of 4/91, and the other part of its genome is highly similar to that of YX10. The results of the phylogenic analysis show that the entire genome of QY16 and most of the QY16 genes are located in the same cluster as those of YX10, except for the S1 gene which is located in the same cluster with that of 4/91. It has been further confirmed by the RDP and SimPlot analysis that QY16 is a recombinant strain deriving from YX10 (as the major parental sequence) and 4/91 (as the minor parental sequence), and that the recombination occurs in a region which includes the 3’-terminal 1b sequence (85 nt) and the 5’-terminal S1 protein gene sequence (1,466 nt). The results of the vaccination-challenge test suggest that QY16 is a nephropathogenic strain of IBV and that the vaccine strains–H120 and 4/91—cannot provide effective protection against it. These results indicate that the continuing evolution of IBV strains by genetic drift and genetic recombination may lead to IBV outbreaks even among the vaccinated chickens in China.

Rapid development and evaluation of a live-attenuated QX-like infectious bronchitis virus vaccine

Infectious bronchitis (IB) is an acute, highly contagious disease, which causes economic losses to the poultry industry worldwide. To control the disease, biosecurity and vaccination are required. In the current research, we rapidly attenuated a QX-like IBV field strain ZYY-2014 using passage in embryos at limiting dilution and tested the safety and efficacy of the attenuated Chinese QX-like IBV strain ZYYR-2014 in 1-day-old specific-pathogen-free (SPF) chickens through spray route. Our result revealed that the attenuated strain presented a decreased pathogenicity in 1-day-old chickens. The strain ZYY-2014 inoculated birds presented typical IBV clinical signs with a mortality of 43%, while the attenuated strain ZYYR-2014 inoculated birds remained healthy. The strain ZYYR-2014 also presented stronger antibody responses and lower viral loads in tracheas, lungs and kidneys. When vaccinated through spray route into 1-day-old SPF chickens, our data suggest a potential of the attenuated ZYYR-2014 strain as a vaccine candidate applied in hatchery, which can contribute in preventing the QX-like IBV infections. Furthermore, attenuation by passage at limiting dilution could be applied for rapid vaccine development against emerging strains.

Preparation and protective efficacy of a chicken embryo kidney cell-attenuation GI-19/QX-like avian infectious bronchitis virus vaccine

Avian infectious bronchitis (IB) is a highly contagious disease, and hazardous to the poultry industry. Immune failure often occurs due to the emergence of new serotypes or field strains antigenically different from the vaccine strains. To prepare a candidate vaccine against the prevalent avian infectious bronchitis virus (IBV) in China, the GI-19/QX-like field isolate Sczy3 was selected as the progenitor strain and attenuated via passaging in chicken embryo kidney (CEK) cells for 100 times. The 100th generation of CEK-adapted strain, designated SczyC100, was safe to use on one-day old specific pathogen-free (SPF) chicken as determined by pathogenicity and virulence reversion test. The efficacies of SczyC100 and two commonly used commercial vaccines (H120 and 4/91) against prevalent GI-19/QX and GI-7/TWI type virulent strains were evaluated. Sczy3C100 effectively reduced the morbidity, mortality, mean lesion scores (MLSs), and viral load of trachea of chickens challenged by GI-19/QX and GI-7/TWI strains. CEK-adapted SczyC100 is therefore a potential vaccine candidate for the control of IB in China.

Assessing the efficacy of a live vaccine against avian encephalomyelitis virus

Avian encephalomyelitis virus (AEV) causes typical neurological symptoms in young chicks and a transient drop in egg production and hatchability in adult laying birds, resulting in huge economic losses in the poultry industry. An effective way to control and prevent this disease is vaccination of the flocks. Here, we assessed the efficacy of the live vaccine candidate strain GDt29 against avian encephalomyelitis virus. The GDt29 strain has low virulence, was confirmed safe, and showed no signs of pathogenicity. High titers of AEV-specific antibodies were detected in GDt29-vaccinated hens (S/P > 3.0) and their progeny (S/P > 2.0). Moreover, the eggs of GDt29-vaccinated hens with high levels of maternal antibodies were hatched successfully regardless of challenge with a heterologous AEV strain, and the GDt29 attenuated vaccine showed higher protective efficacy against AEV than the commercial vaccine. Furthermore, contact-exposed chicks bred with GDt29-vaccinated birds generated high titers against AE virus (S/P > 2.8). Collectively, our studies are proof of the principle that GDt29 might be an ideal vaccine candidate to prevent AEV infection, and they highlight the utility of using a live vaccine against AEV.

Epidemiology and characterization of avian infectious bronchitis virus strains circulating in southern China during the period from 2013-2015

Two hundred and six strains of avian infectious bronchitis virus (IBV) were isolated from chickens showing signs of disease in southern China during the period from 2013–2015. The nucleotide and amino acid sequences from the isolated field strains were compared to 42 published references. Nucleotide homologies ranged from 63.1–99.9% and amino acid homologies ranging from 60.2–100%. At least seven IBV genotypes were co-circulating in commercial chicken farms in southern China. The IBV isolates were genetically diverse and underwent continuing evolution. The QX-type, TW I-type, and 4/91-type were the most common genotypes during the three-year observation period and accounted for 88.8% of the isolated strains. Notably, the prevalence of the TW I-type strains has been increasing in recent years and has become the most common genotype in China. The emergence of variant IBV strains can be attributed to recombination. Serologic analysis and antigenic 3D cartography of 4 reference and 14 field isolated strains indicated the surveyed IBVs had diverse serology types and that the serotype of the isolated QX-type and TW I-type strains was distinct from the vaccines strains. Therefore, long-term continuing surveillance is necessary for IBV prevention and control.

Identification of a novel recombinant virulent avian infectious bronchitis virus

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A novel IBV variant CK/CH/2010/JT-1 was identified.

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A novel genotypic cluster IBV has emerged in China.

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Isolate CK/CH/2010/JT-1 originated from homologous RNA recombination.

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Isolate CK/CH/2010/JT-1 is highly virulent.

The emergence of new infectious bronchitis virus (IBV) variants is often disastrous in the poultry industry. In this study, an IBV, CK/CH/2010/JT-1, was isolated from an H120- and 4/91-IBV-vaccinated flock in China. Antisera against vaccine strains H120 and 4/91 could not provide effective protection against CK/CH/2010/JT-1 in virus neutralization assays. CK/CH/2010/JT-1 could cause 43.75% mortality with respiratory and severe renal lesions in inoculated chickens. Phylogenetic analysis of the S1 gene showed that CK/CH/2010/JT-1 and 31 other isolates could be grouped as a new genotypic cluster. Recombination analysis revealed that three recombination events could be found in the genome of CK/CH/2010/JT-1 at positions 24709-365, 17160-19811 and 21136-21770. Whole-genome sequence analysis showed that CK/CH/2010/JT-1 originated from multiple template switches among QX-like, CK/CH/LSC/99I-, tl/CH/LDT3/03- and 4/91-type IBVs. All of these data demonstrated that CK/CH/2010/JT-1 is a new recombinant genotype IBV with high virulence. Our findings suggest that the surveillance of new genotype strains of IBV is very important for developing more effective anti-IBV strategies.

Genome sequence and origin analyses of the recombinant novel IBV virulent isolate SAIBK2

Recombination between infectious bronchitis viruses (IBVs), together with point mutations, insertions, and deletions, is thought to be responsible for the emergence of new IBV variants. SAIBK2 is a nephropathogenic strain isolated from layer flocks vaccinated with live attenuated H120 vaccine in Sichuan province, China in 2011. SAIBK2 causes severe kidney lesions and results in 50 % mortality in 30-day-old specific-pathogen-free chickens (with a dose of 10⁵ EID₅₀/0.1 mL SAIBK2 per chicken). The complete genome of SAIBK2 consists of 27669 nucleotides, excluding the poly-A tail at the 3′ end. SAIBK2 has the highest identity to YX10 in terms of complete genome. Phylogenetic analysis of complete sequence showed that SAIBK2 belongs to the most dominant genotype in China. Comparison and recombination analyses with other IBV strains revealed that SAIBK2 may originate from recombination events among a YX10-, a YN-, and a Mass-like strain. Furthermore, whole gene 5 and parts of nsp 3, nsp 4, nsp 16, and N genes are involved in the recombination events, and the uptake of these regions from YN and Mass strains by SAIBK2 may increase its replication efficiency and be responsible for its increased virulence in specific-pathogen-free chickens.

Prediction and identification of novel IBV S1 protein derived CTL epitopes in chicken

Infectious bronchitis virus (IBV) is a major pathogen common in the poultry industry. Broad cytotoxic T lymphocyte (CTL) response against IBV is one of the crucial factors that help to control viral replication. Spike glycoproteins on the surface of the IBV virion harbor major T cell epitopes. In this study, based on the peptide-binding motifs of chicken MHC I molecules for the BF2*4, BF2*12, BF2*15, and BF2*19 haplotypes, potential CTL epitopes were predicted using S1 proteins from different IBV strains. Twenty-one peptides were predicted to be potential CTL epitopes; they were manually synthesized and the CTL responses to them tested in vitro. Spleen lymphocytes were collected from specific-pathogen free (SPF) chicken that had been immunized with the S1 protein expression plasmid, pV-S1, and were stimulated by the synthesized peptides. IFN-γ secretion and CD8(+) T cell proliferation in chickens were tested by ELISpot array and flow cytometry, respectively. Four epitopes (P8SRIQTATDP, P9SRNATGSQP, P18GAYAVVNV, and P19SRIQTATQP) were identified to stimulate CD8(+) T cell proliferation and IFN-γ secretion, indicating their efficacy as CTL epitopes in chicken. Poly-CTL-epitope DNA vaccine (pV-S1T) was constructed by inserting nucleotide sequences encoding the P8, P9, P18, and P19 CTL epitopes into the pVAX1 vector. Chickens were vaccinated with either pV-S1, pV-S1T, or pVAX1 and the protection efficacy was analyzed, revealing that ninety percent of chickens immunized with pV-S1T were protected after challenge with 10(6) ELD50 of IBV, demonstrating that these novel CTL epitopes were effective against IBV challenge. This study provides a new method to screen virus CTL epitopes in chicken and to develop poly-CTL-epitope DNA vaccines.

Successful cross-protective efficacy induced by heat-adapted live attenuated nephropathogenic infectious bronchitis virus derived from a natural recombinant strain

A natural recombinant nephropathogenic K40/09 strain of infectious bronchitis virus (IBV) was heat-adapted for possible future use as live attenuated vaccine. The K40/09 strain was selected during successive serial passages in specific-pathogen free (SPF) embryonated eggs at sub-optimal higher temperature (56 °C). Unlike the parental strain, the attenuated strain, designated K40/09 HP50, was found to be safe in 1-day-old SPF chicks, which showed neither mortality nor signs of morbidity, and rarely induced ciliostasis or histological changes in the trachea and kidney after intraocular and fine-spray administration. K40/09 HP50 provided almost complete protection against two distinct subgroups of a nephropathogenic strain (KM91-like and QX-like subgroup) and elicited the production of high titers of neutralizing antibody (neutralization index of 3.6). We conclude that the K40/09 HP50 vaccine virus is rapidly attenuated by heat adaptation and exhibits the desired level of attenuation, immunogenicity, and protective efficacy required for a live attenuated vaccine. These results indicate that the K40/09 vaccine could be helpful for the reduction of economic losses caused by recently emergent nephropathogenic IBV infection in many countries.