Porcine proliferative enteropathy: transmission dynamics and immune response

Abstract

Lawsonia intracellularis is a gram negative, intracellular bacterium that affects pigs and other species. In pigs, it produces porcine proliferative enteropathy (PPE), a costly problem in the swine industry worldwide. This gastrointestinal disease mainly affects the small intestinal tract. The symptoms can be subclinical, with loss of average daily gain (ADG), which can easily become chronic with soft, watery diarrhea, producing uneven growth rates. The less common acute form of the disease, porcine hemorrhagic enteropathy (PHE), occurs in finishing pigs and replacement gilts, producing bloody diarrhea, weakness, depression and sometimes sudden death. Vaccination against Lawsonia intracellularis, with an oral live attenuated isolate of the bacterium or more recently with a killed intramuscular bacterin, is available to help control the infection. However, a comprehensive comparison of the impact that vaccination has on the transmission and induced immunity in vaccinated animals is needed in order to choose the right intervention in farms that may result in reducing transmission rates and generating immunological response. In this thesis, I aimed to 1) compare the impact of vaccination on the transmission of L. intracellularis and 2) compare the impact of vaccination on the local and systemic immune responses of vaccinated and non-vaccinated pigs. The results from my studies highlight the importance of vaccination in the control of L. intracellularis. The length of L. intracellularis shedding as well as the transmission rate were reduced after both oral and intramuscular vaccination. The systemic immune response represented by serological IgG antibodies were stronger in the intramuscularly vaccinated group, while local immune responses represented by secretory IgA in the intestinal lumen and the cell mediated immunity were similarly induced from both vaccination protocols. The results demonstrated in this thesis contribute to the better understanding of the epidemiology, transmission and immune responses to L. intracellularis in vaccinated pigs, using the two commercially available vaccines.