Mitigating the Impact of Infectious Coryza in Commercial Layers through the Use of Live Vaccine against Avibacterium paragallinarum

Commodities

• Animals: poultry

Practices

• Animal Production: animal protection and health, vaccines

Poultry growers face a significant challenge posed by the resurgence of Infectious Coryza (IC), an infectious respiratory disease of chickens. The recent increase in the prevalence and severity of IC could be due to changes in pathogen genotype, virulence, and/or failure of the current vaccines. Inactivated vaccines against Avibacterium paragallinarum (AP) do not provide long-lasting and comprehensive protection from IC. Therefore, there is an urgent need to develop a safe, more effective, and cross-protective vaccine against the emerging AP strains. We have identified two AP strains, isolated from asymptomatic commercial flocks in Ohio, with defects in crucial virulence genes. These strains were non-pathogenic in specific-pathogen-free (SPF) chickens during a challenge trial. Based on these preliminary findings, we propose to evaluate the safety and efficacy of these strains as live vaccine candidates in commercial layers. The safety of the live vaccine candidates will be measured based on the clinical signs score and live body weight in challenged chickens. If deemed safe, the efficacy will be measured based on the vaccines’ ability to protect chickens against challenge from virulent field strain of AP. The proposed live vaccines could be effective alternatives to the currently available inactivated AP vaccines. Furthermore, the proposed vaccines, if successful will be more cost-effective in terms of production and administration, compared to current vaccines. The vaccines will reduce the economic burden faced by poultry growers due to persistent and increasing outbreaks of IC in commercial poultry flocks.

Objectives

The project aims to mitigate the economic burden faced by poultry growers in the Northeastern United States, due to IC affecting poultry flocks, especially layer and breeder chickens. The goal of this proposed study is to provide poultry growers and the US poultry industry with a safe, effective, low-cost, and easy-to-administer, live attenuated vaccine against Avibacterium paragallinarum (AP). The proposed vaccine candidate can reduce the impact of IC in susceptible chickens. The specific objectives of the proposed NE-SARE project are as follows:

1. To determine the safety of the two live vaccine candidates in the commercial layers.  

The safety of the two avirulent strains named AP36_OH_21 and AP37_OH_21 will be determined based on the clinical signs scores, and live body weight of the chickens after challenge inoculation with the vaccine candidates. We have already established that the vaccine candidates are not pathogenic in the SPF chickens. Based on the preliminary findings from the pathogenicity trial in SPF chickens and the observation of multiple defective virulence genes from the in-silico study, we hypothesize that the two vaccine candidates will be safe and produce no adverse effects in commercial layers as well.

2. To evaluate the efficacy of the live-vaccine candidates against the challenge from virulent field strain of Avibacterium paragallinarum in commercial layers.

The efficacy of the vaccine candidates AP36_OH_21 and AP37_OH_21 will be assessed based on the reduction in the clinical sign scores and the amount of bacterial shedding in the vaccinated groups compared to the unvaccinated control groups. We hypothesize that the two live vaccine candidates will elicit strong immunity which will reduce the bacterial colonization and severe clinical signs caused by virulent field strains of the AP in the commercial layers.