Comparison of protection efficacy of toxoid and whole-cell vaccines against porcine pleuropneumonia caused by endotracheal infection with Actinobacillus pleuropneumoniae

Abstract

Porcine pleuropneumonia caused by Actinobacillus pleuropneumoniae poses a continuous risk of contagious disease in large production units of pigs. This study was focused on comparison of protectivity of whole-cell inactivated vaccine containing Actinobacillus pleuropneumoniae serotype 9 and a toxoid vaccine containing Apx I, Apx II, Apx III toxins and outer membrane protein (OMP). Twenty-one piglets from a commercial pleuropneumonia-free herd were used in the experiment. Piglets were randomly divided to three groups, seven animals in each. Animals of the first group were vaccinated with the toxoid vaccine and those of the second group were treated with the whole-cell inactivated vaccine. The third group was an untreated control. Piglets aged 6 weeks were vaccinated for the first time and revaccinated at the age of 10 weeks. Two weeks following revaccination i.e. at the age of 12 weeks, piglets were inoculated endotracheally with a field strain A. pleuropneumoniae serotype 9, to yield an inoculum of 3.2 × 107 CFU/pig. Experimental infection resulted in the development of clinical pleuropneumonia in all animals. The survival rates were 100%, 71.4% and 14.3% in the first, second and third group, respectively. The clinical course of infection differed among the groups. In animals vaccinated with the toxoid vaccine clinical state turned to normal from day 3 following infection, in those vaccinated with whole-cell vaccine it was from day 5, and in untreated animals the symptoms persisted over the whole experimental period. The experiment was terminated 7 days following infection by sacrificing the piglets that survived the infection, and the degree of pulmonary lesions was determined at necropsy. Pulmonary scores were 6.3, 17.8 and 29.0 in animals vaccinated with the toxoid vaccine, whole-cell vaccine and non-vaccinated ones, respectively. Microbiological examinations confirmed the presence of A. pleuropneumoniae following the infection in tonsils.