Efficacy in Reduction of Lung Lesions of a Toxin Expressing Whole-cell Vaccine Against Multiple Serovars of Actinobacillus Pleuropneumoniae in Growing Pigs

Abstract

Background: Actinobacillus pleuropneumoniae is a major economically significant bacterial respiratory pathogen of pigs, and vaccine use is considered an integral control method to prevent disease. The objective of this multi-study analysis was to evaluate the serovar independent efficacy in growing pigs of the C-vaccine (Coglapix®, Ceva, France), which comprises whole cells of A. pleuropneumoniae serovars 1 and 2 expressing ApxI, ApxII and ApxIII toxins. Efficacy was based on protection against lung lesions, since there is good correlation between the severity/extension of lung lesions and losses induced by pleuropneumonia. Vaccine efficacy was determined against challenge with the most common serovars (1, 2, 4, 5, 6, 7, 9/11 and 13) of A. pleuropneumoniae in a total of 13 studies of the same design and reproducibility was validated.Results: Protection against homologous serovars 1 and 2 significantly reduced lung lesion scores (LLS) compared to the positive controls: p = 0.00007 and p = 0.00124, respectively. The protection against heterologous serovars 4, 5, 6, 7, 9/11, and 13 also significantly reduced LLS: range p = 2.9e-10 to p = 0.00953. Reproducibility between challenge studies was excellent with the estimated random effect of study (the fraction of the total variation attributed by differences between studies) being only 2.6%, 2.2% and 4.8% for three serovar 2, two serovar 9/11 and serovar 4 challenge studies, respectively. An outlier was the 35% of variation attributable to trial between the two serovar 6 challenges, possibly explained by a Streptococcus spp. outbreak.Conclusions: A highly significant serovar independent reduction of pathological lung lesions by the C-vaccine was demonstrated for all the serovars tested (1, 2, 4, 5, 6, 7, 9/11 and 13). High levels of protection with similar significance-values were obtained for both homologous and heterologous serovar challenge. To our knowledge the aerosol chamber challenge concept based on accurate individual pig dosing and a standardized biologically weighted lung lesion scoring is the first to be validated statistically as reproducible and reliable. The C-vaccine was demonstrated to be a good candidate to fulfil the demands in the field for an A. pleuropneumoniae-vaccine i.e., high protective capability against disease caused by multiple serovars.