Characterization of the complete genome, antigenicity, pathogenicity, tissue tropism, and shedding of a recombinant avian infectious bronchitis virus with a ck/CH/LJL/140901-like backbone and an S2 fragment from a 4/91-like virus

Potential Transcriptional Enhancers in Coronaviruses: From Infectious Bronchitis Virus to SARS-CoV-2

Coronaviruses constitute a global threat to human and animal health. It is essential to investigate the long-distance RNA-RNA interactions that approximate remote regulatory elements in strategies, including genome circularization, discontinuous transcription, and transcriptional enhancers, aimed at the rapid replication of their large genomes, pathogenicity, and immune evasion. Based on the primary sequences and modeled RNA-RNA interactions of two experimentally defined coronaviral enhancers, we detected via an in silico primary and secondary structural analysis potential enhancers in various coronaviruses, from the phylogenetically ancient avian infectious bronchitis virus (IBV) to the recently emerged SARS-CoV-2. These potential enhancers possess a core duplex-forming region that could transition between closed and open states, as molecular switches directed by viral or host factors. The duplex open state would pair with remote sequences in the viral genome and modulate the expression of downstream crucial genes involved in viral replication and host immune evasion. Consistently, variations in the predicted IBV enhancer region or its distant targets coincide with cases of viral attenuation, possibly driven by decreased open reading frame (ORF)3a immune evasion protein expression. If validated experimentally, the annotated enhancer sequences could inform structural prediction tools and antiviral interventions.

Molecular characterization of a novel variant of infectious bronchitis virus from field outbreaks in backyard chicken population of North East India

Infectious bronchitis virus (IBV) causes considerable economic impacts on global poultry production. Since its emergence in early 1930, IBV continues to evolve and now exists in a wide range of antigenically and genetically distinct variants, that makes the prevention and the control of the disease both complex and challenging. Although IBV has been reported regularly from different corner of India, information about the molecular epidemiology of circulating strain in relation to clinical form of the disease is not available. We have studied the clinico-pathology and confirmed eight distinct field outbreaks of the disease from poultry population of Mizoram, India. The clinical disease in affected birds resulted sever pathological lesions involving respiratory, gastrointestinal, and urinary system together. The complete S1 nucleotide sequences and protein analyses have revealed a distinct variant of genotype I-IBV (GI), designated as GI-24 circulating in India. The S1 protein of the field strains displayed unique additional eighteen amino acids at C terminal end when compared with M41strain. Comparison of the S1 protein among all the 27 lineages of GI revealed five mutations that are exclusive to only the Indian strains. All the field strains have also possessed the amino acid mutations at highly variable region 2 (HVR2) of S1 receptor-binding domain (RBD) that are considered characteristic of nephropathogenic strains. The circulating GI-24 strains displayed potency for a wide range of tropism from respiratory epithelium to GIT and urinary system. This study provides insight on recently emerging IBV outbreaks in NER, India, which might be causing huge economic losses to the poultry farmers in the region.

Development and Immunoprotection of Bacterium-like Particle Vaccine against Infectious Bronchitis in Chickens

Infectious bronchitis (IB) is a major threat to the global poultry industry. Despite the availability of commercial vaccines, the IB epidemic has not been effectively controlled. The exploration of novel IBV vaccines may provide a new way to prevent and control IB. In this study, BLP-S1, a bacterium-like particle displaying the S1 subunit of infectious bronchitis virus (IBV), was constructed using the GEM-PA surface display system. The immunoprotective efficacy results showed that BLP-S1 can effectively induce specific IgG and sIgA immune responses, providing a protection rate of 90% against IBV infection in 14-day-old commercial chickens. These results suggest that BLP-S1 has potential for the development of novel vaccines with good immunogenicity and immunoprotection.

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.

Phylogenetic and Spatiotemporal Analyses of the Complete Genome Sequences of Avian Coronavirus Infectious Bronchitis Virus in China During 1985-2020: Revealing Coexistence of Multiple Transmission Chains and the Origin of LX4-Type Virus

Infectious bronchitis (IB) virus (IBV) causes considerable economic losses to poultry production. The data on transmission dynamics of IBV in China are limited. The complete genome sequences of 212 IBV isolates in China during 1985–2020 were analyzed as well as the characteristics of the phylogenetic tree, recombination events, dN/dS ratios, temporal dynamics, and phylogeographic relationships. The LX4 type (GI-19) was found to have the highest dN/dS ratios and has been the most dominant genotype since 1999, and the Taiwan-I type (GI-7) and New type (GVI-1) showed an increasing trend. A total of 59 recombinants were identified, multiple recombination events between the field and vaccine strains were found in 24 isolates, and the 4/91-type (GI-13) isolates were found to be more prone to being involved in the recombination. Bayesian phylogeographic analyses indicated that the Chinese IBVs originated from Liaoning province in the early 1900s. The LX4-type viruses were traced back to Liaoning province in the late 1950s and had multiple transmission routes in China and two major transmission routes in the world. Viral phylogeography identified three spread regions for IBVs (including LX4 type) in China: Northeastern China (Heilongjiang, Liaoning, and Jilin), north and central China (Beijing, Hebei, Shanxi, Shandong, and Jiangsu), and Southern China (Guangxi and Guangdong). Shandong has been the epidemiological center of IBVs (including LX4 type) in China. Overall, our study highlighted the reasons why the LX4-type viruses had become the dominant genotype and its origin and transmission routes, providing more targeted strategies for the prevention and control of IB in China.

Identification of Novel T-Cell Epitopes on Infectious Bronchitis Virus N Protein and Development of a Multi-epitope Vaccine

Cellular immune responses play a key role in the control of viral infection. The nucleocapsid (N) protein of infectious bronchitis virus (IBV) is a major immunogenic protein that can induce protective immunity. To screen for potential T-cell epitopes on IBV N protein, 40 overlapping peptides covering the entirety of the N protein were designed and synthesized. Four T-cell epitope peptides were identified by gamma interferon (IFN-γ) enzyme-linked immunosorbent spot (ELISpot), intracellular cytokine staining, and carboxyfluorescein succinimidyl ester (CFSE) lymphocyte proliferation assays; among them, three peptides (N_211-230, N_271-290, and N_381-400) were cytotoxic T lymphocyte (CTL) epitopes, and one peptide (N_261-280) was a dual-specific T-cell epitope, which can be recognized by both CD8⁺ and CD4⁺ T cells. Multi-epitope gene transcription cassettes comprising four neutralizing epitope domains and four T-cell epitope peptides were synthesized and inserted into the genome of Newcastle disease virus strain La Sota between the P and M genes. Recombinant IBV multi-epitope vaccine candidate rLa Sota/SBNT was generated via reverse genetics, and its immune protection efficacy was evaluated in specific-pathogen-free chickens. Our results show that rLa Sota/SBNT induced IBV-specific neutralizing antibody and T-cell responses and provided significant protection against homologous and heterologous IBV challenge. Thus, the T-cell epitope peptides identified in this study could be good candidates for IBV vaccine development, and recombinant Newcastle disease virus-expressing IBV multi-epitope genes represent a safe and effective vaccine candidate for controlling infectious bronchitis. IMPORTANCE T-cell-mediated immune responses are critical for the elimination of IBV-infected cells. To screen conserved T-cell epitopes in the IBV N protein, 40 overlapping peptides covering the entirety of the N protein were designed and synthesized. By combining IFN-γ ELISpot, intracellular cytokine staining, and CFSE lymphocyte proliferation assays, we identified three CTL epitopes and one dual-specific T-cell epitope. The value of T-cell epitope peptides identified in the N protein was further verified by the design of an IBV multi-epitope vaccine. Results show that IBV multi-epitope vaccine candidate rLa Sota/SBNT provided cross protection against challenges with a QX-like or a TW-like IBV strain. So, T-cell-mediated immune responses play an important role in the control of viral infection, and conserved T-cell epitopes serve as promising candidates for use in multi-epitope vaccine construction. Our results provide a new perspective for the development of a safer and more effective IBV vaccine.

Genetic and pathogenic characterization of a novel recombinant avian infectious bronchitis virus derived from GI-1, GI-13, GI-28, and GI-19 strains in Southwestern China

Avian infectious bronchitis (IB), caused by avian infectious bronchitis virus (IBV), is an acute and highly contagious disease that is extremely harmful to the poultry industry throughout the world. The cross-using of different attenuated live vaccine strains has led to the occurrence of diverse IBV serotypes. In this study, we isolated an IBV strain from a chicken farm in southwest China and designated it CK/CH/SCMY/160315. Construction of a phylogenetic tree based on full S1 gene sequence analysis suggested that CK/CH/SCMY/160315 bears similarity to GI-28, and further comparison of S1 amino acid residues revealed that CK/CH/SCMY/160315 showed mutations and deletions in many key positions between LDT3-A and other GI-28 reference strains. Importantly, CK/CH/SCMY/160315 was identified as a novel recombinant virus derived from live attenuated vaccine strains H120 (GI-1), 4/91 (GI-13), LDT3-A (GI-28), and the field strain LJL/08-1 (GI-19), identifying at least 5 recombination sites in both structural and accessory genes. Pathogenicity analysis indicated that CK/CH/SCMY/160315 caused listlessness, sneezing, huddling, head shaking, and increased antibody levels in the inoculated chickens. To further describe pathogenicity of this novel strain, we assessed viral load in different tissues and conducted hematoxylin and eosin (HE) staining of the trachea, lungs and kidneys. Our results provide evidence for the continuing evolution of IBV field strains via genetic recombination and mutation, leading to outbreaks in the vaccinated chicken populations in China.

Genotyping of infectious bronchitis viruses isolated in Japan during 2008-2019

Seventeen isolates of infectious bronchitis virus (IBV) were obtained from various prefectures of Japan during 2008-2019 and genetically analyzed. The IBV isolates were classified into six genetic groups, based on phylogenetic analysis of the S1 gene. The S1 genotypes were distinguishable by a newly developed restriction fragment length polymorphism (RFLP) method using three endonucleases, Hae II, Hpa I, and Fok I. Moreover, the isolates were classified into four genetic groups, based on phylogenetic analysis of the S2 gene. However, novel genetic groups based on a combination of S1 and S2 genotypes, which were undetected previously, were confirmed in this study, indicating that various recombinant IBV strains were prevalent in poultry in Japan.

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.

Evaluation of the reproductive system development and egg-laying performance of hens infected with TW I-type infectious bronchitis virus

The prevalence of TW I-type infectious bronchitis virus (IBV) has been increasing rapidly, and it has become the second most common genotype of IBV in China threatening the poultry industry. In this study, 1-day-old specific-pathogen-free (SPF) chickens infected with TW I-type IBV were continuously observed for 200 days. TW I-type IBV affected the respiratory, urinary, and female reproductive systems, resulting in a mortality rate of 10% as well as a decrease in egg quantity and an increase in inferior eggs. During the monitoring period, serious lesions occurred in the female reproductive system, such as yolk peritonitis, a shortened oviduct, and cysts of different sizes with effusion in the degenerated right oviduct. The infective viruses persisted in vivo for a long time, and due to the stress of laying, virus shedding was detected again after the onset of egg production. Our findings suggest that TW I-type IBV is deadly to chickens and could cause permanent damage to the oviduct, resulting in the poor laying performance of female survivors and decreasing the breeding value and welfare of the infected flock.

Evolutionary Analysis of Infectious Bronchitis Virus Reveals Marked Genetic Diversity and Recombination Events

In the last 5 years, frequent outbreaks of infectious bronchitis virus (IBV) are observed in both broiler and layer chicken flocks in the Kingdom of Saudi Arabia (KSA) in spite of extensive usage of vaccines. The IBV is a widespread avian coronavirus affecting both vaccinated and unvaccinated chicken flocks and is attributed to significant economic losses, around the globe. In the present study, 58 (n = 58) samples were collected from four different commercial poultry flocks from 8 KSA districts during 2019. A total of nine positive isolates (9/58; 15.5%), based on real-time reverse transcriptase PCR targeting nucleocapsid (N) gene, were used for further genetic characterization and evolutionary analysis. Genetic characterization of the partial spike (S1) gene revealed the clustering of the reported isolates into three different genotypes, whereas four additional isolates were grouped within 4/91 genotype, two isolates within IS/885 genotype, one isolate was closely related to IS/1494/06, and two isolates were grouped within classic serotype (vaccine-like strains). Phylodynamic revealed clustering of four isolated viruses within GI-13 lineage, three isolates within GI-23 lineage, and two isolates within GI-1 lineage. Results indicate that there are high evolutionary distances between the newly identified IBV strains in this study and the commercially used vaccines (GI-1), suggesting that IBV strains circulating in the KSA are under constant evolutionary pressures. Selective pressure biostatistics analyses consistently demonstrate the presence of a higher positive score which highlights the role of natural selection, a mechanism of virus evolution on sites located on the protein surface, within or nearby domains involved in viral attachment or related functions. Recombination analysis revealed emergence of two isolates through recombination events resulting in new recombinant viruses. Taken together, these finding demonstrate the genetic and evolutionary insights into the currently circulating IBV genotypes in KSA, which could help to better understand the origin, spread, and evolution of infectious bronchitis viruses, and to ascertain the importance of disease monitoring as well as re-evaluation for the currently used vaccines and vaccination programs.

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.

Genetic Analysis of Avian Coronavirus Infectious Bronchitis Virus in Yellow Chickens in Southern China over the Past Decade: Revealing the Changes of Genetic Diversity, Dominant Genotypes, and Selection Pressure

The high mutation rates of infectious bronchitis virus (IBV) pose economic threats to the poultry industry. In order to track the genetic evolutionary of IBV isolates circulating in yellow chickens, we continued to conduct the genetic analyses of the structural genes S1, E, M, and N from 64 IBV isolates in southern China during 2009–2017. The results showed that the dominant genotypes based on the four genes had changed when compared with those during 1985–2008. Based on the S1 gene phylogenetic tree, LX4-type (GI-19) was the most dominant genotype, which was different from that during 1985–2008. The second most dominant genotype was LDT3-A-type, but this genotype disappeared after 2012. New-type 1 (GVI-1) isolates showed increasing tendency and there were four aa (QKEP) located in the hypervariable region (HVR) III and one aa (S) insertion in all the New-type 1 isolates. Both the analyses of amino acid entropy and molecular evolutionary rate revealed that the variations from large to small were S1, E, M, and N. Purifying selection was detected in the S1, E, M, and N gene proteins, which was different from the positive selection during 1985–2008. Six isolates were confirmed to be recombinants, possibly generated from a vaccine virus of the 4/91-type or LDT3-A-type and a circulating virus. The estimated times for the most recent common ancestors based on the S1, E, M, and N genes were the years of 1744, 1893, 1940, and 1945, respectively. Bayesian skyline analysis revealed a sharp decrease in genetic diversity of all the four structural genes after 2010 and since late 2015, the viral population rapidly rose. In conclusion, the IBVs circulating in southern China over the past decade have experienced a remarkable change in genetic diversity, dominant genotypes, and selection pressure, indicating the importance of permanent monitoring of circulating strains and the urgency for developing new vaccines to counteract the emerging LX4-type and New-type IBVs.

Genetic and biological characteristics of four novel recombinant avian infectious bronchitis viruses isolated in China

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Two IBV strains were proved to be originated from multiple recombination events.

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Viruses with very similar S1 gene sequences showed varying biological features.

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Point mutations were observed in the RBD and HVRs of the recombinant viruses.

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Point mutations likely have an effect on these differences in biological characteristics.

Infectious bronchitis viruses (IBVs) of GI-13 (793/B) and GI-19 (QX/LX4) lineages have been frequently detected in China in recent years. Naturally recombinant IBVs originating from the GI-13 and GI-19 lineages have also been isolated from chicken flocks with respiratory and renal problems in China. Thorough genetic and biological investigations of these recombinant viruses have led to speculation regarding their origin, evolution, and control. In order to confirm the previous results and further extend our understanding about the characteristics of the four recombinant IBV strains we had previously identified (I0718/17, I0722/17, I0724/17, and I0737/17), we conducted phylogenetic analysis by comparing their complete S1 gene sequences with those of 71 reference strains of different genotypes and lineages. We identified a close relationship between the S1 sequences of the four strains and those of GI-13 strains. The results of complete genome sequence analysis confirmed the previously identified recombination events in the four IBV strains and revealed additional recombination events in different genomic regions of strains I0718/17 and I0724/17, suggesting that the two strains originated from multiple recombination events between 4/91-like and YX10-like viruses. We comparatively evaluated the antigenicity, pathogenicity, and affinity of the four recombinant viruses and their deduced parental strains in the trachea and kidneys. Some of the strains showed comparable antigenic relatedness, pathogenicity, and affinity for the trachea and kidneys among each other and with their parental viruses; however, some of them showed varying biological characteristics. Point mutations observed in the receptor-binding domain and hypervariable region of the S1 subunit of the spike protein likely have an effect on these differences in biological characteristics, although the influence of other factors—such as host innate-immune responses and changes in genomic regions beyond the S1 protein—might also be responsible for such changes.