EFFECTS OF ENDOBRONCHIAL CHALLENGE WITH ACTINOBACILLUS-PLEUROPNEUMONIAE SEROTYPE-9 OF PIGS VACCINATED WITH INACTIVATED VACCINES CONTAINING THE APX TOXINS

The efficacy of two inactivated vaccines containing the Apx toxins of Actinobacillus pleuropneumoniae (Hemopig(TM), Biokema, Lausanne, Switz erland and Porcilis(TM) APP, Intervet, Boxmeer, the Netherlands) was d etermined. Ten pigs were vaccinated twice with Hemopig(TM) and eight p igs with Porcilis(TM) App. Ten control animals were injected twice wit h a saline solution. Three weeks after the second vaccination, all pig s were endobronchially inoculated with 10(5) colony-forming units (CFU ) of an A. pleuropneumoniae serotype 9 strain. Increased respiratory r ate and/or fever were observed in all vaccinated and control pigs afte r challenge. One pig of the Hemopig(TM) group and of the Porcilis(TM) App group died, whereas all pigs of the control group survived the cha llenge. Surviving pigs were killed at 7 days after challenge. The mean percentage of affected lung tissue was 34% in the control group, 16% in the Hemopig(TM) group, and 17% in the Porcilis(TM) App group. A. pl europneumoniae was isolated from the lungs of all 10 control animals, from 7 of the 10 animals vaccinated with Hemopig(TM) and from 5 of the 8 animals vaccinated,vith Porcilis(TM) App. The mean bacterial titres of the caudal lung lobes were 1.4x10(6) CFU/g in the control group, 1 .7x10(3) CFU/g in the Hemopig(TM) group, and 4.8x10(3) CFU/g in the Po rcilis(TM) App group. In both vaccinated groups the mean number of day s with dyspnoea, the mean number of days with fever, the mean percenta ge of affected lung tissue, and the mean bacterial titre in the caudal lung lobes were significantly lower than in the control group, Signif icant differences between the two vaccinated groups were not observed. It was concluded that both vaccines induced partial protection.