F4+ Escherichia coli in piglets: effect of host characteristics on population dynamics

Post-weaning diarrhoea (PWD) is a multifactorial disease of newly-weaned piglets that occurs in the first two weeks after weaning. PWD causes growth retardation and increased mortality, resulting in reduced animal welfare and economical damage. The main causative agent of PWD is enterotoxigenic Escherichia coli expressing F4 fimbriae (F4+ E. coli ).Intervention measures for F4+ E. coli can be aimed at preventing diarrhoea or at preventing transmission and should be evaluated in challenge or transmission studies.In this thesis, transmission of F4+ E. coli was studied and quantified. Factors affecting the population dynamics of this bacterium were investigated in individual piglets and at population level. Special interest was taken in the F4 receptor (F4R), a specific adhesion site for F4+ E. coli in the small intestine. Not all pigs express F4R; pigs with adhesive (F4R+) and non-adhesive brush borders (F4R-) can be distinguished by in vitro adhesion tests.

The set up and analysis of transmission experiments with F4+ E. coli are described in this thesis and a definition of the infectious state based on the shedding patterns of individual animals was developed. No indication was found that reinfection affected the population dynamics of F4+ E. coli .

F4R+ piglets were found to be more susceptible to become infectious than F4R- piglets. It was concluded that the F4R status of the pig has a strong effect on the population dynamics of F4+ E. coli . The F4R status should therefore be used as a co-variate in the statistical analysis of F4 + E. coli intervention studies, both in challenge and transmission studies.The level of transmission is mainly dependent on the fraction of F4R+ piglets in the population.By reducing the fraction of F4R+ piglets in the population to <0.09 large outbreaks of F4+ E. coli will be prevented.

The heterogeneity in susceptibility may serve as a point of departure to control F4+ E. coli by selective breeding for F4R- pigs. With a simple discrete model, it was illustrated that selective breeding for F4R- piglets by using F4R- boars, is an effective way to reduce the fraction of F4R+ piglets in the population, given the presence of a sensitive F4R status test.