A Quantitative Study on the Direct and Indirect Campylobacter Transmission in Broilers Under Experimental Conditions

Mathematical modelling is a useful tool in addressing questions in veterinary epidemiology. It can be used to evaluate measures taken to sufficiently reduce transmission of infection. Horizontal transmission of Campylobacter is probably the most important route of introduction. To eradicate Campylobacter from broiler flocks, transmission between broilers and broiler flocks has to be reduced to the extent that persistence of Campylobacter becomes impossible. The aim of this study was to gain a better understanding of the population dynamics of Campylobacter. To this end, we studied three decisive parameters, i) the infectious dose that is necessary to successfully colonize a broiler, through challenge shedding experiments, ii) the extent of direct spread between broilers through transmission experiments with broilers that are housed in groups, and iii) the extent of indirect transmission between broilers through transmission experiments with individually housed broilers. In addition we also tested the effect of acidified drinking water, as possible control measure, on all of these three aspects. We found that the probability for a broiler to become Campylobacter colonized depends on the dose at which the broiler is exposed to. In addition acidified drinking water seems to increase the dose necessary to successfully colonize a broiler. Once a broiler is colonized however, Campylobacter will spread fast to (almost) all broilers within the flock, regardless infectious dose or water treatment. This implies that to reduce the Campylobacter prevalence one should concentrate on the reduction of indirect transmission. The extent of transmission of infectious agents is determined by the infectivity of infectious individuals and the susceptibility of uninfected individuals. Our results give rise to new research questions, how is the (indirect) transmission of Campylobacter influenced by the infectivity of colonized broilers or by the susceptibility of Campylobacter free broilers, which are currently under investigation.