Work package 3

Does the route of exposure to pathogens determine the potential for colonisation and expression of virulence genes?

Work with Salmonella in chickens demonstrated that airborne exposure is much more efficient in producing infection than exposure by feeding. Similar data are available for pigs, but control of airborne infections by management is much more difficult. However, measures aimed at improving disease resistance must be effective against all routes of entry.

The hypothesis underlying the work in this programme is that microbial load in the environment determines the level and route of exposure of individual animals to pathogens and commensals, and that the route of exposure determines the numbers of organisms required to colonise different sites. This will be examined by comparing airborne and oral challenge with Salmonella Enteritidis ands S. Typhimurium. The ability of the pathogen to persist in the face of local immune responses in respiratory and intestinal mucosal will be examined and compared. The importance of expression of specific pathogen genes for survival in the two mucosal sites will be determined using signature-tagged-mutagenesis libraries.

The work proposed will identify the relative risks associated with exposure of animals to pathogens in air (contaminated dust, aerosols from other animals etc.) or by contamination of surfaces, food or water (the oral route). These results will identify targets for farm-based intervention in further work. In addition, comparative data on the local and systemic immune responses after different routes of challenge will contribute to future work on vaccine development.