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 is estimated that 60-80% of cases are attributed to handling or consumption of chicken. Our previous studies demonstrated that caecal Campylobacter levels in chickens can be significantly reduced by subcutaneous vaccination with recombinant 6xHis-CjaA. However, protection was modest and late in the life of broiler birds. To improve the magnitude and timing of protection, other candidate antigens were screened. Twenty two 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 birds and three conferred up to 2 log10 CFU/g reductions in caecal Campylobacter carriage at 49-56 days post-primary vaccination on the day of hatch across at least three independent trials. In a single trial, no improvement of the protective effect was noted using a double or triple combination of the antigens found to be protective. The induction of specific serum IgY antibodies against the Campylobacter antigens used was demonstrated but the kinetics of antigen-specific humoral responses did not correlate with protection. Measurement of caecal IgA levels is ongoing. Preliminary analysis of splenocyte recall responses in birds vaccinated with one of the protective antigens revealed a correlation between the level of proliferation and the Campylobacter caecal counts in vaccinated birds. Future trials will further investigate the nature of the immune responses and whether they can repel heterologous challenge in broilers at commercial stocking density.