Epsilon Open Archive

Abstract

In recent years several incidents of feed-borne spread of Salmonella spp. have been documented in Swedish pig herds, including serotypes previously not associated with pigs. In this thesis two feed-associated serotypes (S Cubana and S Yoruba) were compared with two serotypes commonly detected in pigs (S Typhimurium and S Derby). The overall aim of the thesis was to increase knowledge about the feed-associated serotypes, with special focus on their infection dynamics in pigs. In 2003, a contamination in a feed mill caused the spread of S Cubana via feed to a number of pig herds. Questions raised during that outbreak led to the design of the present PhD project. The outbreak was analysed and in experimental studies pigs were inoculated orally with one of four serotypes, in three different doses (103, 106 or 109 colony forming units). Pigs were then monitored for eight weeks in order to determine differences among serotypes in faecal shedding, serological response and body distribution. Differences among serotypes were revealed as regards infectious dose, serological response and distribution to extra-intestinal organs and tissues. The data obtained were used for a mathematical modelling approach on the dynamics of faecal salmonella shedding and the immune response in pigs. The results showed that the dynamics of faecal shedding during infection were strongly associated with the challenge dose but weakly associated with the infection serotype. In order to investigate transmission of the four serotypes, uninfected pigs were introduced to salmonella-shedding pigs in a late stage of infection as well as to contaminated pens. All four serotypes were transmitted to at least one of the naïve pigs, but the overall transmission was low in both experimental settings. In conclusion, these studies showed that S Cubana may differ in some aspects regarding infection dynamics in pigs. However, the inoculation dose had a larger impact than the serotype. Thus, the level of infection in a herd infected with Salmonella spp. may be more indicative of what control measures that are needed, than the serotype involved.