Transmissibility of Infectious Bronchitis Virus H120 Vaccine Strain Among Broilers Under Experimental Conditions

Infectious bronchitis virus: an overview of the "chicken coronavirus"

Infectious bronchitis virus (IBV) is a highly contagious avian Gammacoronavirus that affects mainly chickens (Gallus gallus) but can circulate in other avian species. IBV constitutes a significant threat to the poultry industry, causing reduced egg yield, growth and mortality levels that can vary in impact. The virus can be transmitted horizontally by inhalation or direct/indirect contact with infected birds or contaminated fomites, vehicles, farm personnel and litter (Figure 1). The error-prone viral polymerase and recombination mechanisms mean diverse viral population results, with multiple genotypes, serotypes, pathotypes and protectotypes. This significantly complicates control and mitigation strategies based on vigilance in biosecurity and the deployment of vaccination.

Hassan MS, C. Cork S, Abdul-Careem MF. Infectious Bronchitis Coronavirus Infection in Chickens: Multiple System Disease with Immune Suppression

In the early 1930s, infectious bronchitis (IB) was first characterized as a respiratory disease in young chickens; later, the disease was also described in older chickens. The etiology of IB was confirmed later as being due to a coronavirus: the infectious bronchitis virus (IBV). Being a coronavirus, IBV is subject to constant genome change due to mutation and recombination, with the consequence of changing clinical and pathological manifestations. The potential use of live attenuated vaccines for the control of IBV infection was demonstrated in the early 1950s, but vaccine breaks occurred due to the emergence of new IBV serotypes. Over the years, various IBV genotypes associated with reproductive, renal, gastrointestinal, muscular and immunosuppressive manifestations have emerged. IBV causes considerable economic impacts on global poultry production due to its pathogenesis involving multiple body systems and immune suppression; hence, there is a need to better understand the pathogenesis of infection and the immune response in order to help developing better management strategies. The evolution of new strains of IBV during the last nine decades against vaccine-induced immune response and changing clinical and pathological manifestations emphasize the necessity of the rational development of intervention strategies based on a thorough understanding of IBV interaction with the host.

Evaluation of protection conferred by a vaccination program based on the H120 and CR88 commercial vaccines against a field variant of avian infectious bronchitis virus

Due to serotype variations among different avian infectious bronchitis viruses isolated in Tunisia since 2000, protection of chicks, especially broiler flocks, with Mass H120 vaccine often fails. Therefore, association of CR88 (793B type) with H120 vaccines was used for better response. Challenge experiments were then conducted to evaluate tracheal and renal cross-protection in chickens immunized via nasal and eye drops. Conferred protection was measured by clinical signs and macroscopic lesions observed, based on scores attributed according to their severities. The results showed a low protection conferred by H120 alone, as vaccination did not reduce tracheal and kidney lesions (70% scored as 3) after TN20/00 virus challenge, which also led to 10% mortality. Conversely, the challenge results indicated that the combination of the 2 strains (H120/CR88) allow high protection. Based on the results of the challenge experiments, a vaccination protocol coupling CR88 to H120 was applied for industrial broiler flocks. Clinical observations and serological results confirmed that association of heterologous serotypes (H120 and CR88 vaccines) increased the levels of protection against infectious bronchitis viruses compared with the H120 vaccine given alone.

Vaccine or field strains: the jigsaw pattern of infectious bronchitis virus molecular epidemiology in Poland

Infectious bronchitis (IB), caused by infectious bronchitis virus (IBV), account for severe economic losses in the poultry industry. The continuous emergence of a multitude of IBV variants poses many challenges for its diagnosis and control, and live attenuated vaccines, despite their routine use, still plays a significant role in driving IBV evolution, further complicating the epidemiological scenario. Unfortunately, the impact of different vaccination strategies on IB control, epidemiology, and diagnosis has rarely been investigated. This work presents the results of a large-scale diagnostic survey performed in Poland to study IBV molecular epidemiology and how vaccination may affect the viral circulation in the field. To this purpose, 589 samples were collected between May 2017 and January 2019, tested by reverse transcription-PCR for IBV and sequenced. Vaccine and field strains were discriminated based on genetic and anamnestic information. The most commonly detected lineages were 793B (79%) and variant 2 (17.4%), with sporadic detections of QX, Mass, and D274-like strains. Most of the detected strains had a vaccine origin: 46.3% matched one of the applied vaccines, while 36.5% were genetically related to vaccines not implemented in the respective protocol. Besides their practical value for the proper planning of vaccination protocols in Poland, these results suggest that only a fraction (17.2%) of the circulating strains are field ones, imposing a careful assessment of the actual IBV field menaces. Moreover, phenomena like vaccine spreading and persistence seem to occur commonly, stressing the need to further study the epidemiological consequences of the extensive use of live vaccines.

The 3D8 single chain variable fragment protein suppress infectious bronchitis virus transmission in the transgenic chickens

Infectious bronchitis (IB) generated by the infectious bronchitis virus (IBV) causes economic difficulties for livestock farmers. The 3D8 single chain variable fragment (scFv) protein is a recombinant antibody with nuclease activity that shows antiviral effects against various DNA and RNA viruses in mice and chickens. In this experiment, 3D8 scFv G₂ transgenic chickens produced by crossing 3D8 scFv G₁ transgenic rooster and wild type hens were screened by genomic PCR and immunohistochemistry analysis. 3D8 scFv transgenic chickens, wild type sibling chickens, and SPF chickens were directly infected with IBV (5 chickens per group) and indirectly infected by airborne propagation (15 chickens per group). The relative IBV shedding titers were measured by quantitative real-time PCR using oropharyngeal and cloacal swabs on days 3 and 5 after intraocular infection. The viral load was significantly decreased in the 3D8 scFv transgenic chickens from the contact transmission group. Additionally, blood was collected from each group on day 17 post-infection. The ELISA results showed a marked reduction of the antibody titer against IBV in the 3D8 scFv transgenic chickens from the contact transmission group. These results suggest that the 3D8 scFv protein potentially inhibits infectious bronchitis virus transmission in chickens.

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Produced G2 3D8 single chain  variable  fragment (scFv) transgenic chickens.

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3D8 scFv transgenic chickens showed reduced infectious bronchitis viral shedding level in the  contact transmission group.

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3D8 scFv transgenic chickens were 40% lower than the response in the control groups in IBV serum antibody titer.

Genetic diversity of avian infectious bronchitis virus in China in recent years

In this study, 213 infectious bronchitis viruses (IBVs) were isolated from samples collected from 801 flocks suspected to be infected with IBV from January 2016 to December 2017 in China. By using complete nucleotide sequences of S1 gene we determined the phylogeny of these IBV isolates, which in turn allowed us to define six lineages/genotypes, a number of recombinants and a novel variant. The GI-19 lineage was the most frequently isolated type in China in recent years. Although scattered mutations in the S1 gene among the GI-19 lineage viruses were observed, we also noted different sublineages in the GI-19 lineage with unique mutations, suggesting a high degree of S1 gene variation since they were first isolated in the mid-1990s. We also isolated a number of vaccine-like viruses from vaccinated diseased chickens, although more work is needed to differentiate the reisolation of vaccine strains from field strains of the same serotype. One of the important findings in this study is that the prevalence of the TW I type viruses in GI-7 lineage has been increasing in recent years in China. Another important finding is that recombination events occurred between the predominant GI-19 lineage and the commonly used 4/91 vaccine, which gave rise to distinct IBV isolates. In addition, a novel IBV isolate, together with a reference strain in GenBank database, were found to form a novel lineage/genotype that was remarkably distinct from established lineages. The characteristics of the antigenicity, tissue tropism, pathogenicity and complete genome were required for further investigation for the recombinants and the viruses in different sublineages and novel lineages. Meanwhile, permanent monitoring of circulating strains was needed to monitor the emerging viruses and rationally modify vaccination strategies in the field situation.

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The GI-19 lineage was the most frequently isolated type in China in recent years.

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Different sub-lineages were found in the GI-19 lineage with unique mutations.

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A number of vaccine-like viruses were isolated from vaccinated diseased chickens.

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The TW I type viruses in GI-13 lineage has been increasing in recent years in China.

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A novel IBV isolate was found to form a novel clade that was distinct from established lineages.

Genetics, antigenicity and virulence properties of three infectious bronchitis viruses isolated from a single tracheal sample in a chicken with respiratory problems

Three different IBV genotypes/serotypes, designated ck/CH/LDL/150434–I (LDL/150434–I), ck/CH/LDL/150434–II (LDL/150434–II) and ck/CH/LDL/150434–III (LDL/150434–III), were detected in a single tracheal sample from a chicken showing signs of respiratory disease. The viruses were isolated using a cross-neutralization test and limiting dilution in embryonated specific-pathogen-free (SPF) eggs. Isolate LDL/150434–I was a re-isolation of H120 vaccine strain that was introduced into the chicken flock by vaccination, transmitted between chickens, and later accumulated several genomic mutations. Isolate LDL/150434–II was a novel variant that originated from recombination events between H120 and ck/CH/LDT3/03-like viruses. The widespread use of H120 vaccine, which offered incomplete protection against heterotypic IBVs in the fields, may play important roles in the emergence of such a novel genetic variant. Based on the analysis of S1 and complete genomic sequence, isolate LDL/150434–III was related genetically but distinct from the established strains of nrTW I type viruses of GI-7 lineage circulating in Mainland China since 2009. The three IBV isolates were avirulent when they infected SPF chickens. Furthermore, synergistic effects on pathogenicity were not observed when the different types co-infected the SPF chickens. However, the isolates persisted in the respiratory tracts longer in combined infected birds than those in individual infected birds. The results provide insights into the evolution of the viruses and co-infection of chickens with different virus serotypes.

Phylodynamic analysis and molecular diversity of the avian infectious bronchitis virus of chickens in Brazil

Avian infectious bronchitis virus (IBV) is the etiological agent of a highly contagious disease, which results in severe economic losses to the poultry industry. The spike protein (S1 subunit) is responsible for the molecular diversity of the virus and many sero/genotypes are described around the world. Recently a new standardized classification of the IBV molecular diversity was conducted, based on phylogenetic analysis of the S1 gene sequences sampled worldwide. Brazil is one of the biggest poultry producers in the world and the present study aimed to review the molecular diversity and reconstruct the evolutionary history of IBV in the country. All IBV S1 gene sequences, with local and year of collection information available on GenBank, were retrieved. Phylogenetic analyses were carried out based on a maximum likelihood method for the classification of genotypes occurring in Brazil, according to the new classification. Bayesian phylogenetic analyses were performed with the Brazilian clade and related international sequences to determine the evolutionary history of IBV in Brazil. A total of 143 Brazilian sequences were classified as GI-11 and 46 as GI-1 (Mass). Within the GI-11 clade, we have identified a potential recombinant strain circulating in Brazil. Phylodynamic analysis demonstrated that IBV GI-11 lineage was introduced in Brazil in the 1950s (1951, 1917-1975 95% HPD) and population dynamics was mostly constant throughout the time. Despite the national vaccination protocols, our results show the widespread dissemination and maintenance of the IBV GI-11 lineage in Brazil and highlight the importance of continuous surveillance to evaluate the impact of currently used vaccine strains on the observed viral diversity of the country.

Factors influencing the outcome of infectious bronchitis vaccination and challenge experiments

The factors influencing the outcome of infectious bronchitis vaccination and challenge experiments regarding the respiratory and renal systems are reviewed. Advantages and disadvantages of the available techniques for measuring protection against an infectious bronchitis virus challenge are discussed, including the definition of protection itself. Suggestions are made regarding some ways in which progress towards standardization of a recognized protocol for performing experimental challenge studies can be made and areas where more work is needed are indicated.

Progress and challenges toward the development of vaccines against avian infectious bronchitis

Avian infectious bronchitis (IB) is a widely distributed poultry disease that has huge economic impact on poultry industry. The continuous emergence of new IBV genotypes and lack of cross protection among different IBV genotypes have been an important challenge. Although live attenuated IB vaccines remarkably induce potent immune response, the potential risk of reversion to virulence, neutralization by the maternal antibodies, and recombination and mutation events are important concern on their usage. On the other hand, inactivated vaccines induce a weaker immune response and may require multiple dosing and/or the use of adjuvants that probably have potential safety risks and increased economic burdens. Consequently, alternative IB vaccines are widely sought. Recent advances in recombinant DNA technology have resulted in experimental IB vaccines that show promise in antibody and T-cells responses, comparable to live attenuated vaccines. Recombinant DNA vaccines have also been enhanced to target multiple serotypes and their efficacy has been improved using delivery vectors, nanoadjuvants, and in ovo vaccination approaches. Although most recombinant IB DNA vaccines are yet to be licensed, it is expected that these types of vaccines may hold sway as future vaccines for inducing a cross protection against multiple IBV serotypes.

Comparison of vaccine subpopulation selection, viral loads, vaccine virus persistence in trachea and cloaca, and mucosal antibody responses after vaccination with two different Arkansas Delmarva Poultry Industry -derived infectious bronchitis virus vaccines

Factors responsible for the persistence of Arkansas Delmarva Poultry Industry (ArkDPI)-derived infectious bronchitis vaccines in commercial flocks and the high frequency of isolation of ArkDPI-type infectious bronchitis viruses in respiratory cases are still unclear. We compared dynamics of vaccine viral subpopulations, viral loads, persistence in trachea and cloaca, and the magnitude of infectious bronchitis virus (1BV)-specific antibody induction after vaccination with two commercial ArkDPI-derived Arkansas (Ark) serotype vaccines. One of the vaccines (coded vaccine B) produced significantly higher vaccine virus heterogeneity in vaccinated chickens than the other vaccine (coded A). Chickens vaccinated with vaccine B had significantly higher viral loads in tears at 5 days postvaccination (DPV) than those vaccinated with vaccine A. Vaccine B also induced a significantly higher lachrymal immunoglobulin M response at 11 DPV, an earlier peak of IBV-specific lachrymal immunoglobulin A, and higher serum antibodies than vaccine A. In addition, a significantly higher proportion of birds vaccinated with vaccine B had vaccine virus detected in the trachea at 20 DPV than those vaccinated with vaccine A. Furthermore, the virus detected at 20 DPV in most of the chickens vaccinated with vaccine B was a single specific subpopulation (subpopulation 4) selected from multiple vaccine subpopulations detected earlier at 5 and 7 DPV in the same chickens. On the other hand, a higher proportion of chickens vaccinated with vaccine A had virus detected in cloacal swabs at 20 DPV. Thus we found differences in mucosal antibody induction and selection and persistence of vaccine viruses between two ArkDPI-derived vaccines from different manufacturers. The higher vaccine virus heterogeneity observed in chickens vaccinated with vaccine B compared with those vaccinated with vaccine A may be responsible for these differences. Thus the high frequency of Ark IBV viruses in the field may be due to the inherent ability of some ArkDPI-derived vaccine viruses to be selected and persist in vaccinated chickens. Vaccine virus persistence may offer genetic material for recombination or may undergo mutations with the potential to result in increased virulence.

Molecular characterization of infectious bronchitis virus isolates from Russia and neighbouring countries: identification of intertypic recombination in the S1 gene

Infectious bronchitis virus (IBV) isolates recovered in Russia, Ukraine, and Kazakhstan between 2007 and 2010 were subjected to molecular characterization and compared with those isolated a decade ago. The IBV genome was detected in 202 out of 605 field samples from chickens with various clinical signs. Partial sequencing of the S1 gene revealed 153 vaccine strains and 49 field isolates of several genetic groups. Massachusetts, 793/B and D274 remained the predominant IBV genotypes along with QX, whereas B1648, Italy-02, Arkansas and variants accounted for about 12% of the total number. Three IBVs contained recombinant S1 gene sequences comprising genome fragments of QX-type field isolates and vaccine strains H120 (UKR/02/2009) or 4/91 (RF/03/2010), and vaccine strains H120 and D274 (RF/01/2010). The results of the present study showed a significant decline in prevalence of variant IBVs and a further spread of QX-type isolates in commercial chicken flocks in Russia as compared with the 1998 to 2002 data.

Attenuated live vaccine usage affects accurate measures of virus diversity and mutation rates in avian coronavirus infectious bronchitis virus

The full-length genomes of 11 infectious bronchitis virus (IBV) field isolates from three different types of the virus; Massachusetts (Mass), Connecticut (Conn) and California (CAL) isolated over a 41, 25 and 8 year period respectively, were sequenced and analyzed to determine the mutation rates and level of polymorphisms across the genome. Positive selection was not detected and mutation rates ranged from 10(-4) to 10(-6)substitutions/site/year for Mass and Conn IBV types where attenuated live vaccines are routinely used to control the disease. In contrast, for CAL type viruses, for which no vaccine exists, positive selection was detected and mutation rates were 10 fold higher ranging from 10(-2) to 10(-3)substitutions/site/year. Lower levels of genetic diversity among the Mass and Conn viruses as well as sequence similarities with vaccine virus genomes suggest that the origin of the Mass and all but one of the Conn viruses was likely vaccine virus that had been circulating in the field for an unknown but apparently short period of time. The genetic data also identified a recombinant IBV isolate with 7 breakpoints distributed across the entire genome suggesting that viruses within the same serotype can have a high degree of genetic variability outside of the spike gene. These data are important because inaccurate measures of genetic diversity and mutation rates could lead to underestimates of the ability of IBV to change and potentially emerge to cause disease.

Efficacy of infectious bronchitis virus vaccinations in the field: association between the alpha-IBV IgM response, protection and vaccine application parameters

Infectious bronchitis virus (IBV) is, in spite of vaccination, still a major cause of respiratory problems in broilers and of poor egg production in breeders and layers in many parts of the world. A possible cause of the insufficient protection induced by vaccination is an inadequate application of the vaccine. This paper reports the results of two field studies. In the first, the results of the alpha-IBV IgM enzyme-linked immunosorbent assay (ELISA) on post-vaccination sera were compared with the efficacy of the IBV vaccination against homologous challenge of the same broilers. The results showed that groups with at least 50% positive sera in the IgM ELISA at 10 days post vaccination had a high level of protection against challenge. Most groups of broilers with a low level of IgM ELISA positives had a low or moderate level of protection against challenge. In a second field study, the IgM response to IBV vaccination was compared with detailed information of the vaccination process of 360 spray-vaccinated flocks of about 2-week-old broilers, layer pullets, broiler breeders and broiler grandparents. The information included parameters such as flock size, type of chicken, housing, age of the chicken, application route, vaccine, dose, water quantity and temperature, ventilation and light management, combination with other vaccines and temperature of the house. The aim was to identify factors that might be associated positively or negatively with the IgM response and thereby with the expected level of protection against homologous challenge under field conditions. Significant associations were detected between the level of IgM response and factors regarding type of bird, flock size, housing type, ventilation management, light management, age/interval of vaccination, interval between vaccination and blood sampling, and temperature of the water that was used to reconstitute the vaccine. This knowledge can be useful to improve the average efficacy of IBV vaccination in the field.