Genetic mutations in live infectious bronchitis vaccine viruses following single or dual in vitro infection of tracheal organ cultures

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

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

Infectious Bronchitis Virus (Gammacoronavirus) in Poultry Farming: Vaccination, Immune Response and Measures for Mitigation

Infectious bronchitis virus (IBV) poses significant financial and biosecurity challenges to the commercial poultry farming industry. IBV is the causative agent of multi-systemic infection in the respiratory, reproductive and renal systems, which is similar to the symptoms of various viral and bacterial diseases reported in chickens. The avian immune system manifests the ability to respond to subsequent exposure with an antigen by stimulating mucosal, humoral and cell-mediated immunity. However, the immune response against IBV presents a dilemma due to the similarities between the different serotypes that infect poultry. Currently, the live attenuated and killed vaccines are applied for the control of IBV infection; however, the continual emergence of IB variants with rapidly evolving genetic variants increases the risk of outbreaks in intensive poultry farms. This review aims to focus on IBV challenge-infection, route and delivery of vaccines and vaccine-induced immune responses to IBV. Various commercial vaccines currently have been developed against IBV protection for accurate evaluation depending on the local situation. This review also highlights and updates the limitations in controlling IBV infection in poultry with issues pertaining to antiviral therapy and good biosecurity practices, which may aid in establishing good biorisk management protocols for its control and which will, in turn, result in a reduction in economic losses attributed to IBV infection.

Host immune response to infectious bronchitis virus Q1 in two commercial broiler chicken lines

This study investigated the pathogenesis of infectious bronchitis virus (Gammacoronavirus) strain Q1 in two commercial broiler chicken lines, and the host immune response to infection. Chicks from each line were grouped into either infected or control. Following Q1 infection at day-old, fast (Line-A) and slow (Line-B) growing chicks were monitored for clinical signs and body weights. At 3, 7, 9, 14, 21 and 28 days post infection (dpi), five birds were humanely euthanised, and trachea, kidney and proventriculus tissues were collected for quantitative RT-PCR and histopathology. Blood was collected weekly to determine IBV-specific ELISA antibody titres. Q1 infection significantly reduced the body weights of Line-A chicks at 14 and 21 dpi, but there were no significant differences in Line-B. Through qRT-PCR, significantly higher viral loads were found in the trachea, proventriculus and kidney tissues of Line-A chicks at 7-9 dpi. At day-old and at 28 dpi, the mean antibody titre in Line-B was notably higher than Line-A. Significant IFN-α mRNA expression was noted in the trachea and kidneys of Line-A, whereas no change occurred in Line-B. Chicks in Line-B, compared to those in Line-A, demonstrated a tissue-dependent increase of IFN-β, TLR3, IL-1β and IL-6 and LITAF gene transcription responses to IBV Q1. It appears that the level of maternal antibodies, growth rates, and other inherent host genetic factors could have influenced the differences in viral loads and immune responses.

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.

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

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

Co-circulation of genetically diverse population of vaccine related and unrelated respiratory mycoplasmas and viruses in UK poultry flocks with health or production problems

Respiratory diseases continue to have a major impact on poultry health, welfare and productivity. However, little information is available on their current status in UK poultry flocks. We investigated the presence of four economically important respiratory pathogens in healthy or problematic flocks; infectious bronchitis virus (IBV), avian metapneumovirus (aMPV), Mycoplasma gallisepticum (Mg) and Mycoplasma synoviae (Ms). Samples from 131 UK poultry flocks were received during the 12 month study period. Oropharyngeal (OP) swabs were taken from eight birds per flock and accompanied with flock health information. The study included 118 chicken, 6 pheasant and 5 turkey flocks, and 1 quail and 1 partridge flock. Chicken flocks were of layers (n = 98), broilers (n = 15), breeders (n = 3) and undisclosed (n = 2). Flock ages ranged from 3 to 72 weeks old, and the average flock size was 17,633 birds. PCR detected 65 (49.6%), 59 (45%) and 8 (6.1%) flocks as positive for IBV, Mg/Ms and aMPV respectively. Analysis of the mgc2 gene of the Mg isolates revealed high similarities to Mg TS-11 and Mg 6/85. Further gene analysis found that the TS-11-like isolates were unrelated to the TS-11 vaccine. Multi-locus sequence typing (MLST) analysis identified the majority of positive Ms as ST21, along with ST2 (MS-H-like), ST6 and ST43. IBV S1 gene sequencing identified strains as 793B (66.7%), Arkansas (23.8%) and Massachusetts (9.5%). All aMPV positive samples belonged to subtype B. Findings indicate that over half of the flocks sampled were positive for at least one of the four vaccine or field strains of mycoplasmas or viruses.