Development of a divalent vaccine targeting Campylobacter in poultry production

Campylobacter is the leading cause of foodborne illnesses in the United States. According to FoodNet, the incidence of Campylobacter is the highest (19.2 cases per 100,000 population) among foodborne pathogenic bacteria and increased by 7% in 2022. Campylobacter infections not only cause gastrointestinal infection symptoms but also lead to severe post-infection complications, such as Guillain-Barré Syndrome, a neurological disorder causing muscular paralysis and even death. C. jejuni and C. coli are the major pathogenic species that are frequently involved in food contamination and human infection. Of the two species, C. jejuni accounts for the majority of infections, whereas C. coli is responsible for the remaining cases. While C. jejuni and C. coli commonly inhabit the gastrointestinal tract of a range of livestock, such as beef cattle, dairy cattle, swine, chicken, and turkey, they are most frequently transmitted to humans from contaminated poultry meat. Approximately 90% of broiler flocks in the United States are colonized by Campylobacter. Controlling Campylobacter in poultry production has proven to be difficult.Preharvest control of Campylobacter is crucial for reducing the risk of human illnesses and deaths caused by poultry contamination. Birds can be infected with Campylobacter through various environmental sources, such as contaminated water, feed, and wildlife, and once present, Campylobacter persists in the flock. Quantitative microbial risk assessment has shown that a 1-2 order of magnitude reduction in the level of Campylobacter in poultry intestines could decrease the risk of human Campylobacteriosis by 44% and 95%. Similarly, a 2-order of magnitude reduction of Campylobacter counts on chicken carcasses would decrease human campylobacteriosis 30-fold. Ongoing research is focused on developing intervention strategies to control Campylobacter at the preharvest level. Particularly, vaccination is considered an effective strategy to control Campylobacter in poultry production.The development of effective Campylobacter vaccines for poultry requires careful consideration of several unique features. First, vaccination should overcome antigenic variations resulting from the extensive diversity in Campylobacter genomes. Second, vaccination should be able to control both C. jejuni and C. coli. The two species coexist in the gastrointestinal tract of poultry and are commonly isolated from poultry meat. Therefore, Campylobacter vaccines must be effective in reducing both species in poultry. Third, the vaccine should be convenient to administer to large numbers of birds preferably via drinking water. This will reduce the need for individual injections, which can be time-consuming and labor-intensive. Fourth, poultry vaccination should be affordable for poultry producers. The cost of vaccination should be feasible for on-farm applications and should not outweigh the benefits of reduced Campylobacter levels in poultry populations. Fifth, bacterial vaccines typically take several weeks to elicit immune responses and become effective. Vaccines for broiler chickens should become effective within the short production cycle of the bird. Sixth, vaccines administered to birds should not remain on carcasses, since residual organisms can lead to false positive results, which can hinder regulatory compliance and delay product release. Seventh, most importantly, poultry vaccination should reduce the risk of Campylobacter contamination of poultry meat.Live-attenuated vaccines are live bacteria that present various antigenic molecules on their cell surface and stimulate robust, long-lasting immunity. In contrast, killed vaccines demonstrate limited Campylobacter inhibition in poultry despite the use of adjuvants and boosters to enhance host immune response. Live-attenuated vaccines resist enzymatic degradation when passing through the gastrointestinal tract, whereas recombinant subunit vaccines are prone to proteolytic degradation. Moreover, live-attenuated vaccines cost less to produce than killed vaccines and subunit vaccines, which require additional steps to inactivate pathogens and purify recombinant proteins. Importantly, our previous results demonstrate that a live-attenuated C. jejuni vaccine significantly reduced the level of Campylobacter in chickens within the short lifespan of broilers with a single oral administration.Leveraging our previous study, we aim to develop an oral water-based, divalent vaccine targeting both C. jejuni and C. coli for broiler production. Our long-term goal is to develop vaccines to control Campylobacter in poultry. The goal of this specific research proposal is to develop a live-attenuated divalent vaccine to control C. jejuni and C. coli in broiler chickens to reduce Campylobacter contamination of chicken meat, the primary source of human campylobacteriosis. To attain the goal, we will pursue the three objectives.1) Construct a divalent Campylobacter vaccine targeting C. jejuni and C. coli. We have already constructed an effective live-attenuated C. jejuni vaccine in our previous study. Here, we will first construct a C. coli vaccine and evaluate the efficacy of a divalent vaccine against the two species in chickens by measuring the levels of Campylobacter colonization and Campylobacter-specific host immunity. 2) Establish oral administration of a divalent vaccine via drinking water in poultry. Poultry vaccination through drinking water is a common method to administer vaccines to large numbers of birds. We will determine the dosage for vaccination via drinking water and evaluate vaccination efficacy.3) Assess the effect of vaccination on the reduction of Campylobacter contamination of chicken carcasses. The purpose of poultry vaccination is to reduce Campylobacter contamination of poultry products. Additionally, it is important to note that live-attenuated vaccines should not remain on poultry carcasses to ensure safety. The vaccine strains in our research are unable to survive on carcasses due to their increased susceptibility to oxygen and peroxyacetic acid, an oxidizing antimicrobial agent used to control carcass contamination during poultry processing. To evaluate the impact of poultry vaccination on food safety, we will measure the level of Campylobacter on chicken carcasses and confirm the absence of the vaccine strains on carcasses.Through these efforts, this project will contribute to food safety by developing an effective divalent vaccine to control Campylobacter in poultry production.