Evaluation of a novel recombinant strain of infectious bronchitis virus emerged from three attenuated live vaccine strains

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.

An Amplicon-Based Application for the Whole-Genome Sequencing of GI-19 Lineage Infectious Bronchitis Virus Directly from Clinical Samples

Infectious bronchitis virus (IBV) causes a highly contagious respiratory disease in chickens, leading to significant economic losses in the poultry industry worldwide. IBV exhibits a high mutation rate, resulting in the continuous emergence of new variants and strains. A complete genome analysis of IBV is crucial for understanding its characteristics. However, it is challenging to obtain whole-genome sequences from IBV-infected clinical samples due to the low abundance of IBV relative to the host genome. Here, we present a novel approach employing next-generation sequencing (NGS) to directly sequence the complete genome of IBV. Through in silico analysis, six primer pairs were designed to match various genotypes, including the GI-19 lineage of IBV. The primer sets successfully amplified six overlapping fragments by long-range PCR and the size of the amplicons ranged from 3.7 to 6.4 kb, resulting in full coverage of the IBV genome. Furthermore, utilizing Illumina sequencing, we obtained the complete genome sequences of two strains belonging to the GI-19 lineage (QX genotype) from clinical samples, with 100% coverage rates, over 1000 × mean depth coverage, and a high percentage of mapped reads to the reference genomes (96.63% and 97.66%). The reported method significantly improves the whole-genome sequencing of IBVs from clinical samples; thus, it can improve understanding of the epidemiology and evolution of IBVs.

Differential analysis of IBV-infected primary chicken embryonic fibroblasts and immortalized DF-1

Infectious bronchitis virus (IBV), the causative agent of infectious bronchitis, is responsible for major economic losses in the poultry industry worldwide. While IBVs can usually be passaged in primary chicken embryonic fibroblasts (CEFs), most of the wild ones cannot adapt to passaged cell lines. In this study, the wild strain CK/CH/MY/2020 was used to infect primary CEF and immortalize DF-1 CEF cells. Results indicated that IBV was able to cause lesions and pass onto CEF, but not DF-1. Indeed, the virus could enter DF-1 cells and synthesize the associated structural gene but could not assemble into complete viral particles for release. Furthermore, transcriptome sequencing analysis showed significant differences in gene expression between CEF and DF-1 cells after viral infection, although the corresponding antiviral responses could be activated in both cell types. The biggest difference was in terms of the amino acid biosynthesis pathway and the cytokine receptor interaction pathway, which were significantly and specifically activated in CEF. This could actually explain why intact viruses can be assembled but not in DF-1. In addition, SLBP and P2RX7 affect the replication of IBV's structural genes to some extent. Overall, IBV can enter CEF and DF-1 cells, but the complex intracellular cytokine interactions affect the assembly and release of viral particles. The insight will be useful for the study of IBV through in vitro transmission and pathogenesis.

IMPORTANCE

Infectious bronchitis virus (IBV) is responsible for high morbidity and mortality as well as substantial economic losses worldwide. Transcriptome sequencing of IBV-infected chicken embryonic fibroblast and DF-1 cells revealed that the virus elicits antiviral immunity in cells after viral infection, but IBV cannot activate DF-1 cells to produce sufficient amounts of viral structures to assemble into complete virions, which may be caused by the interactions between cytokines. The study of IBV cellular adaptations is important for vaccine development and investigation of the pathogenesis of IBV.

Pros and Cons on Use of Live Viral Vaccines in Commercial Chicken Flocks

The poultry industry is the largest source of meat and eggs for the growing human population worldwide. Key concerns in poultry farming are nutrition, management, flock health, and biosecurity measures. As part of the flock health, use of live viral vaccines plays a vital role in the prevention of economically important and common viral diseases. This includes diseases and production losses caused by Newcastle disease virus, infectious bronchitis virus, infectious laryngotracheitis virus, infectious bursal disease virus, Marek's disease virus, chicken infectious anemia virus, avian encephalomyelitis virus, fowlpox virus, and avian metapneumovirus. These viruses cause direct and indirect harms, such as financial losses worth millions of dollars, loss of protein sources, and threats to animal welfare. Flock losses vary by type of poultry, age of affected animals, co-infections, immune status, and environmental factors. Losses in broiler birds can consist of high mortality, poor body weight gain, high feed conversion ratio, and increased carcass condemnation. In commercial layers and breeder flocks, losses include higher than normal mortality rate, poor flock uniformity, drops in egg production and quality, poor hatchability, and poor day-old-chick quality. Despite the emergence of technology-based vaccines, such as inactivated, subunit, vector-based, DNA or RNA, and others, the attenuated live vaccines remain as important as before. Live vaccines are preferred in the global veterinary vaccine market, accounting for 24.3% of the global market share in 2022. The remaining 75% includes inactivated, DNA, subunit, conjugate, recombinant, and toxoid vaccines. The main reason for this is that live vaccines can induce innate, mucosal, cellular, and humoral immunities by single or multiple applications. Some live vaccine combinations provide higher and broader protection against several diseases or strains of viruses. This review aimed to explore insights on the pros and cons of attenuated live vaccines commonly used against major viral infections of the global chicken industry, and the future road map for improvement.

Effect of monovalent and bivalent live attenuated vaccines against QX-like IBV infection in young chickens

Since 1999, QX-like (GI-19) avian infectious bronchitis viruses have been the predominant strains in China till now. Vaccination is the most effective way to control the disease, while live attenuated vaccine is widely used. In the current research, we evaluated the effect of several monovalent and bivalent live IBV vaccines in young chickens against the QX-like (GI-19) IBV infection. The results showed that monovalent 4/91 and bivalent Ma5+LDT3 vaccines could provide efficient protection in day-old chickens that reduced morbidity and mortality, ameliorated histopathology lesions, and reduced viral loads were observed. These data suggest that vaccination through nasal route with monovalent 4/91 or bivalent Ma5+LDT3 in day-old chickens could serve a safe and effective vaccination strategy for controlling QX-like (GI-19) infectious bronchitis virus.

Molecular characterization of the S1 gene in GI-17 and GI-13 type isolates of avian infectious bronchitis virus (IBV) in Costa Rica, from 2016 to 2019

Avian infectious bronchitis is one of the most important respiratory diseases affecting poultry production worldwide. The etiological agent of this disease is the avian infectious bronchitis virus (IBV). We analyzed 14 isolates of IBV obtained from poultry farms in Costa Rica, from 2016 through 2019. We sequenced the S1 region of the genome and the sequences obtained were submitted to GenBank. Phylogenetic analyses showed that the isolates obtained during 2016-2017 belong to the GI-17 lineage and are related to the Georgia 13-type Ga-13/14255/14 and CK/CR/1160/16 variants, with a 96.90-100% nucleotide sequence identity and a 92.25-100% amino acid sequence identity. The main differences were detected in the RBD and HVR-3 regions, where a series of mutations eliminate an N-glycosylation site in 10 out of 11 isolates. The isolates obtained during 2018-2019 belong to the GI-13 lineage and are closely related to the 4/91 vaccine variant, with over 98% sequence identity at the nucleotide and amino acids levels. Variations were detected in the RBD and HVR regions, with a possible N-glycosylation site detected in isolate CK/CR/0632/19. These results indicate that a GA13-like pathogenic variant circulated during the 2016-2017 period and that the 4/91 variant was detected after the introduction of the vaccine. The variations shown in both the GA13-like and 4/91 isolates examined, reveal the need for continuous surveillance of IBV in Costa Rica, to detect new variants that may be introduced to the country or develop during outbreaks. This information is highly relevant for vaccination planning and disease management programs.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13337-022-00762-2.