Effect of IBV-H120 vaccination in broilers on colibacillosis susceptibility after infection with a virulent Massachusetts-type IBV strain

Evaluation of protection and immunity induced by infectious bronchitis vaccines administered by oculonasal, spray or gel routes in commercial broiler chicks

Broiler chicks' responses following combined IBV live attenuated Massachusetts and 793B strains through gel, spray or oculonasal (ON) vaccination routes were cross-compared. Subsequently, the responses following IBV M41 challenge of the unvaccinated and vaccinated groups were also assessed. Post-vaccination humoral and mucosal immune responses, alongside viral load kinetics in swabs and tissues, were determined using commercial ELISA assays, monoclonal antibody-based IgG and IgA ELISA assays and qRT-PCR respectively. After challenged with IBV-M41 strain, humoral and mucosal immune responses, ciliary protection, viral load kinetics, and immune gene mRNA transcriptions between the three vaccination methods were examined and compared. Findings showed that post-vaccinal humoral and mucosal immune responses were similar in all three vaccination methods. Post vaccinal viral load kinetics is influenced by method of administration. The viral load peaked in the ON group within the tissues and the OP/CL swabs in the first and third weeks respectively. Following M41 challenge, ciliary protection and mucosal immune responses were not influenced by vaccination methods as all three methods offered equal ciliary protection. Immune gene mRNA transcriptions varied by vaccination methods. Significant up-regulation of MDA5, TLR3, IL-6, IFN-α and IFN-β genes were recorded for ON method. For both spray and gel methods, significant up-regulation of only MDA5 and IL-6 genes were noted. The spray and gel-based vaccination methods gave equivalent levels of ciliary protection and mucosal immunity to M41 virulent challenge comparable to those provided by the ON vaccination. Analysis of viral load and patterns of immune gene transcription of the vaccinated-challenged groups revealed high similarity between turbinate and choanal cleft tissues compared to HG and trachea. With regards to immune gene mRNA transcription, for all the vaccinated-challenged groups, similar results were found except for IFN-α, IFN-β and TLR3, which were up-regulated only in ON compared to gel and spray vaccination methods.

Broiler resilience to colibacillosis is affected by incubation temperature and post-hatch feeding strategy

Colibacillosis is a poultry disease that negatively affects welfare and causes economic losses. Treatment with antibiotics raises concerns on antimicrobial resistance. Consequently, alternative approaches to enhance poultry resilience are needed. Access to feed and water directly after hatch (early feeding) may enhance resilience at later ages. Additionally, a high eggshell temperature (EST) during mid incubation may improve chick quality at hatch, supporting potential positive effects of early feeding. Effects of EST [37.8°C (control) or 38.9°C (higher)] during mid-incubation (embryo days 7–14) and feeding strategy (early feeding or 48 h delayed feeding) were tested in a 2 × 2 factorial arrangement. At hatch, ~ 1,800 broilers were divided over 36 pens and grown for 6 wk. At d 8 post hatch, avian pathogenic E. coli (APEC) was inoculated intratracheally as model to investigate broiler resilience against respiratory diseases. Incidence and severity of colibacillosis, local infection, and systemic infection were assessed at 6 moments between 3 h and 7 d postinoculation. Broilers were weighed daily during 13 d postinoculation and weekly thereafter. At higher EST, early feeding resulted in higher incidence of systemic infection compared to delayed feeding whereas at control EST, systemic infection was not different between feeding strategies. Regardless of EST, early compared to delayed feeding resulted in lower incidence of local infection, fewer BW deviations, and higher growth until d 35. In conclusion, early feeding could be considered as a strategy to enhance broiler resilience, but only when EST is not too high.

Route of infectious bronchitis virus vaccination determines the type and magnitude of immune responses in table egg laying hens

Chicken immune responses to infectious bronchitis virus (IBV) vaccination can depend on route of administration, vaccine strain and bird age. Typically for layer chickens, IBV vaccinations are administered by spray in the hatchery at day-old and boosted at intervals with live vaccines via drinking water (DW). Knowledge of live attenuated IBV vaccine virus kinetics and the immune response in egg-laying hens is exceptionally limited. Here, we demonstrated dissemination of vaccine viruses and differences in hen innate, mucosal, cellular and humoral immune responses following vaccination with Massachusetts or 793B strains, administered by DW or oculonasal (ON) routes. Detection of IBV in the Mass-vaccinated groups was greater during early time-points, however, 793B was detected more frequently at later timepoints. Viral RNA loads in the Harderian gland and turbinate tissues were significantly higher for ON-Mass compared to all other vaccinated groups. Lachrymal fluid IgY levels were significantly greater than the control at 14 days post-vaccination (dpv) for both vaccine serotypes, and IgA mRNA levels were significantly greater in ON-vaccinated groups compared to DW-vaccinated groups, demonstrating robust mucosal immune responses. Cell mediated immune gene transcripts (CD8-α and CD8-β) were up-regulated in turbinate and trachea tissues. For both vaccines, dissemination and vaccine virus clearance was slower when given by DW compared to the ON route. For ON administration, both vaccines induced comparable levels of mucosal immunity. The Mass vaccine induced cellular immunity to similar levels regardless of vaccination method. When given either by ON or DW, 793B vaccination induced significantly higher levels of humoral immunity.

In vivo typing of Escherichia coli obtained from laying chickens with the E. coli peritonitis syndrome

RESEARCH HIGHLIGHTS

Even at high doses not any E. coli strain can induce EPSSubstantial differences in virulence exist within very virulent E. coli strainsThe embryo lethality test is a useful alternative for biotyping E. coli in laying hensBroiler colibacillosis may represent a source of EPS strains for layers and vice versa.

Factor Influences for Diagnosis and Vaccination of Avian Infectious Bronchitis Virus (Gammacoronavirus) in Chickens

Infectious bronchitis virus (IBV) is a major economic problem in commercial chicken farms with acute multiple-system infection, especially in respiratory and urogenital systems. A live-attenuated and killed vaccine is currently immunized to control IBV infection; however, repeated outbreaks occur in both unvaccinated and vaccinated birds due to the choice of inadequate vaccine candidates and continuous emergence of novel infectious bronchitis (IB) variants and failure of vaccination. However, similar clinical signs were shown in different respiratory diseases that are essential to improving the diagnostic assay to detect IBV infections. Various risk factors involved in the failure of IB vaccination, such as various routes of application of vaccination, the interval between vaccinations, and challenge with various possible immunosuppression of birds are reviewed. The review article also highlights and updates factors affecting the diagnosis of IBV disease in the poultry industry with differential diagnosis to find the nature of infections compared with non-IBV diseases. Therefore, it is essential to monitor the common reasons for failed IBV vaccinations with preventive action, and proper diagnostic facilities for identifying the infective stage, leading to earlier control and reduced economic losses from IBV disease.

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.

Recent approaches for control of E. coli and respiratory complex in Middle East

This study was conducted on 100 one-day-old broiler chicks to evaluate the effect of Poulvac E. coli vaccine in reduction of clinical signs and complications after concurrent infectious bronchitis virus (variant 02) and virulent E. coli O78 challenges. The birds were evaluated for clinical signs, mortality for 7 days post-infection, PM lesion score, average body weight and serological evaluation. Re-isolation and RT-PCR for the challenging infectious bronchitis virus (IBV) variant 02 were conducted thereafter. The results showed that the Poulvac E. coli at one-day old chicks in the presence of co-infection with virulent E. coli and IBV variant 02 provides better body weight gain at 35 days than the other groups. The challenge with IBV variant 02 alone in non-vaccinated birds doesn't give any mortality; this indicated that the severity of IBV variant 02 increased by the presence of co-infection with Avian Pathogenic E. coli (APEc). The mortality percentage associated with both E. coli and IBV variant 02 infections in the none vaccinated group by Poulvac E. coli was 25% while this percentage was 10% of the vaccinated group. The Poulvac E. coli is not negatively affecting the immune response against different concurrent viral vaccines like Infectious bursal disease (IBD), and moreover, it improves the immune response against some others like Newcastle disease virus (NDV), Avian Influenza (AI) H5 and IBV.

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.

Respiratory phagocytes are implicated in enhanced colibacillosis in chickens co-infected with influenza virus H9N2 and Escherichia coli

1. The aim of this study was to determine the most likely time interval after infection with influenza virus H9N2 for co-infection with Escherichia coli to cause colibacillosis, the importance of lung load of E. coli and the involvement of respiratory phagocytes. 2. Specific pathogen free chickens were inoculated intranasally with 10⁶EID₅₀ of influenza virus or uninfected. After specified time intervals, 10⁷ CFU E. coli or phosphate-buffered saline was inoculated. The presence of lesions, the number of respiratory phagocytes in the respiratory lavage fluid and the E. coli load in the lung were determined after different time intervals. 3. Compared with the number of lesions in chickens receiving only E. coli inoculation, the number lesions in co-infected chickens were increased at 0- and 3-d time intervals, but reduced in the groups at 6- and 9-d intervals between co-infection. 4. At 1-3 d after E. coli inoculation, the number of lesions chickens was correlated with the number of respiratory phagocytes harvested and related to the E. coli load in the lungs at 5 d. 5. These results suggest that the lesions caused by E. coli in chickens were increased within a 0-3 d interval following H9N2 virus inoculation and that this effect is related to the number of respiratory phagocytes.

Alternative methods to compare safety of live-attenuated respiratory Newcastle disease vaccines in young chicks

The work reported here is an initial attempt to find an alternative method by which the safety of live-attenuated Newcastle disease virus (NDV) vaccines for the respiratory tract of young chickens can be assessed. The current recommended methods involve either the subjective assessment of respiratory signs, or raise ethical concerns, as in the case of the intracerebral pathogenicity index. The two methods considered here were the use of tracheal organ cultures to assess the level of ciliostasis which the vaccines caused to the ciliated epithelium of the trachea and the incorporation of a pathogenic strain of Escherichia coli in the inoculum in order to induce colibacillosis. Both methods were successful in confirming the safety of the two vaccines. However, these results are only preliminary and more studies need to be performed to determine whether one or both methods have potential, either to replace the existing statutory tests, or provide a test which might be useful during the development stages of a new live-attenuated NDV vaccine.

The efficacy of inactivated Escherichia coli autogenous vaccines against the E. coli peritonitis syndrome in layers

Autogenous Escherichia coli vaccines to prevent the E. coli peritonitis syndrome (EPS) in laying hens are often used in the field, although their effectiveness has not been demonstrated yet. Therefore, in this study, which consisted of two experiments, their efficacy was assessed. In the first experiment, the EPS-inducing ability of three E. coli isolates originating from bone marrow of hens that died due to EPS and with different Pulsed-Field Gel Electrophoresis patterns, was examined by intravenous inoculation of the isolates in 17-week-old brown layers. Based on the results one isolate was chosen for the preparation of the vaccines and for homologous challenge and another one for heterologous challenge performed in the second experiment. In the named experiment, groups of laying hens which had been vaccinated intramuscularly at 14 and 18 weeks of age with inactivated vaccine either formulated as aqueous suspension or as water-in-oil emulsion were homologously or heterologously challenged per aerosol at 30 weeks of age. The vaccines contained ≥10^8.2 formaldehyde-inactivated colony-forming units (cfu) of E. coli per hen dose in 0.5 ml. The estimated E. coli challenge dose uptake ranged from 10^5.8 to 10^6.5 cfu per hen. Groups consisted of 18 hens each and were housed in separate isolators from 27 weeks of age. Control groups were included in this experiment, which was ended eight days after challenge. Vaccinations had no effect on body growth and both vaccine types induced (almost) complete protection against homologous challenge, while protection against heterologous challenge was inconclusive.

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.

Establishment of reverse genetics system for infectious bronchitis virus attenuated vaccine strain H120

Infectious bronchitis virus (IBV) strain H120 was successfully rescued as infectious clone by reverse genetics. Thirteen 1.5-2.8 kb fragments contiguously spanning the virus genome were amplified and cloned into pMD19-T. Transcription grade complete length cDNA was acquired by a modified "No See'm" ligation strategy, which employed restriction enzyme Bsa I and BsmB I and ligated more than two fragments in one T4 ligase reaction. The full-length genomic cDNA was transcribed and its transcript was transfected by electroporation into BHK-21 together with the transcript of nucleocapsid gene. At 48 h post transfection, the medium to culture the transfected BHK-21 cells was harvested and inoculated into 10-days old SPF embryonated chicken eggs (ECE) to replicate the rescued virus. After passage of the virus in ECE five times, the rescued H120 virus (R-H120) was successfully recovered. R-H120 was subsequently identified to possess the introduced silent mutation site in its genome. Some biological characteristics of R-H120 such as growth curve, EID50 and HA titers, were tested and all of them were very similar to its parent strain H120. In addition, both R-H120 and H120 induced a comparable titer of HA inhibition (HI) antibody in immunized chickens and also provided up to 85% of immune protection to the chickens that were challenged with Mass41 IBV strain. The present study demonstrated that construction of infectious clone from IBV vaccine strain H120 is possible and IBV-H120 can be use as a vaccine vector for the development of novel vaccines through molecular recombination and the modified reverse genetics approach.

Veterinary vaccines: alternatives to antibiotics?

The prevention of infectious diseases of animals by vaccination has been routinely practiced for decades and has proved to be one of the most cost-effective methods of disease control. However, since the pioneering work of Pasteur in the 1880s, the composition of veterinary vaccines has changed very little from a conceptual perspective and this has, in turn, limited their application in areas such as the control of chronic infectious diseases. New technologies in the areas of vaccine formulation and delivery as well as our increased knowledge of disease pathogenesis and the host responses associated with protection from disease offer promising alternatives for vaccine formulation as well as targets for the prevention of bacterial disease. These new vaccines have the potential to lessen our reliance on antibiotics for disease control, but will only reach their full potential when used in combination with other intervention strategies.

The role of phagocytic cells in enhanced susceptibility of broilers to colibacillosis after Infectious Bronchitis Virus infection

Colibacillosis results from infection with avian pathogenic Escherichia coli bacteria. Healthy broilers are resistant to inhaled E. coli, but previous infection with vaccine or virulent strains of Infectious Bronchitis Virus (IBV) predisposes birds for severe colibacillosis. We investigated whether IBV affects recruitment and function of phagocytic cells and examined NO production, phagocytic and bactericidal activity, and kinetics of peripheral blood mononuclear cells (PBMC) and splenocytes. Moreover, we measured cytokine mRNA expression in lung and spleen samples. Broilers were inoculated with IBV H120 vaccine or virulent M41 and challenged 5 days later with E. coli 506. A PBS control and E. coli group without previous virus inoculation were also included. Birds were sacrificed at various time points after inoculation (h/dpi). Inoculation with IBV induced extended and more severe colibacillosis than with E. coli alone. At 4 dpi, the number of KUL-01⁺ PBMC in all E. coli-inoculated groups was significantly higher than in PBS-inoculated birds, which correlated with lesion scores. From 1 to 4 dpi, NO production by PBMC from all E. coli-inoculated animals was elevated compared to PBS birds. Bactericidal activity of PBMC in IBV-inoculated animals at 7 dpi was lower than in PBS- and E. coli-inoculated birds, but phagocytic capacity and recruitment were not severely impaired. In spleen samples of IBV-infected animals reduced expression of IL-1β, IL-6, IL-8, IL-10, IL-18 and IFN-γ mRNA was found 1 dpi. Our results suggest that enhanced colibacillosis after IBV infection or vaccination is caused at least by altered innate immunity and less by impairment of phagocytic cell function.

Infectious bronchitis virus: S1 gene characteristics of vaccines used in China and efficacy of vaccination against heterologous strains from China

The entire S1 protein genes of eight infectious bronchitis (IB) vaccine strains used in China were compared with those of the IB virus isolates present in the field in China. The nucleotide and amino acid similarities between the eight IB vaccine strains and the field strain, tl/CH/LDT3/03, which was isolated from a teal (Anas sp.), were not more than 81.1% and 79.2%, respectively. Phylogenetic analysis based on the S1 genes showed that the vaccines and field strains belonged to different clusters and showed larger evolutionary distances, and indicated that they were of different genotypes. Four out of the eight vaccines, in addition to the Massachusetts type vaccine H120, were used for protection tests against challenge by the IB virus isolate tl/CH/LDT3/03. This revealed that each of the five IB vaccines induced poor protection against the teal isolate, as assessed by respiratory protection, clinical signs and mortality, indicating the necessity of developing vaccines from local strains for IB control in China.