Design and evaluation of vaccines for the control of Campylobacter in poultry

Campylobacter is the main cause of foodborne diarrhoeal illness in humans in the developed world and it has been estimated that 60-80% of cases are attributed to handling or consumption of chicken. Our previous studies have demonstrated that caecal Campylobacter levels in chickens can be significantly reduced by oral vaccination with Salmonella Typhimurium ∆aroA strains expressing the C. jejuni antigen CjaA. We evaluated avian pathogenic E. coli (APEC) ∆aroA expressing CjaA as a TetC fusion, or TetC, relative to S. Typhimurium ∆aroA expressing the same antigens. APEC have lower zoonotic potential and a commercially available APEC vaccine (PoulVac® E. coli) is used to control avian colibacillosis. In two trials, neither vaccine decreased caecal Campylobacter levels compared to mock-vaccinated controls, though antigen-specific humoral responses were detected. To screen other candidate antigens, 22 surface-localised and immunogenic Campylobacter proteins were cloned as GST fusions and their solubility was assessed. Nine were purified in sufficient quantities to be evaluated as subunit vaccines in chickens and three conferred up to 2log10 reductions in caecal Campylobacter carriage at 49-56 days post-hatching across at least two independent replicates. Current work will evaluate whether combining the three antigens above confers improved protection and investigates the nature of the protective immune responses.