Comparison of the efficacy of a subunit and a live streptomycin-dependent porcine pleuropneumonia vaccine.

OBJECTIVE: To evaluate the efficacy of two new-generation porcine pleuropneumonia vaccines when challenged with Australian isolates of Actinobacillus pleuropneumoniae of serovars 1 and 15. DESIGN: The Porcilis APP vaccine and an experimental streptomycin-dependent strain of A pleuropneumoniae were evaluated in a standardised pen trial. Each vaccine/challenge group consisted of 10 pigs. RESULTS: With the serovar 1 challenge, the Porcilis APP vaccine and the live vaccine, compared with the control group, gave significant protection in terms of clinical signs, lung lesions, re-isolation scores and average daily gain (ADG) postchallenge. Only the Porcilis APP vaccine provided significant protection against mortality. In the serovar 15 challenged pigs, the only significant difference detected was that the Porcilis APP vaccinated pigs had a better postchallenge ADG than the controls. None of the Porcilis APP vaccinated pigs showed signs of depression postvaccination and none were euthanased after challenge with either serovar 1 or 15. The pigs vaccinated with the live vaccine showed obvious depression after each vaccination and a total of 3 pigs were euthanased after challenge (one with serovar 1 and two with serovar 15). CONCLUSIONS: Both of the vaccines provided significant protection against a severe challenge with serovar 1 A pleuropneumoniae. Neither vaccine was effective against a serovar 15 A pleuropneumoniae challenge. There was evidence that the Porcilis APP vaccine did provide some protection against the serovar 15 challenge because the ADG, after challenge of pigs given this vaccine, was greater than the control pigs.

An evaluation of the role of antibodies to Actinobacillus pleuropneumoniae serovar 1 and 15 in the protection provided by sub-unit and live streptomycin-dependent pleuropneumonia vaccines.

OBJECTIVE: To evaluate the serological response of pigs receiving either the Porcilis APP vaccine or a modified live vaccine based on a streptomycin-dependent (SD) strain of Actinobacillus pleuropneumoniae, and then challenged with an Australian isolate of A. pleuropneumoniae of either serovar 1 or 15 as a means of understanding the protection provided by both vaccines against serovar 1 but not against serovar 15. DESIGN: The serological tests evaluated were serovar-specific polysaccharide ELISA tests (for serovar 1 and 15), ELISA tests for antibodies to three A. pleuropneumoniae toxins (ApxI, ApxII and ApxIII) as well as to a 42 kDa outer membrane protein (OMP), a haemolysin neutralisation (HN) assay and immunoblotting. The tests were used to detect antibodies in vaccinated pigs that had been shown to be protected against serovar 1 but not serovar 15. RESULTS: In the polysaccharide antigen ELISA assays, both vaccines resulted in a significant rise in the titre in the serovar 1 ELISA but not the serovar 15 ELISA. The Porcilis APP vaccinated pigs showed a significant response in the ApxI, ApxIII and 42 kDa OMP ELISA. In the ApxII ELISA, all pigs tested (the Porcilis APP vaccinates and the controls) were positive on entry to the trial. In the HN assay, the Porcilis APP vaccinated pigs showed a significant response after one dose while the SD vaccinated pigs required two doses of vaccine before a marked rise in titre was induced. Immunoblotting revealed that neither vaccine generated antibodies that recognised the ApxIII produced by serovar 15. CONCLUSIONS: The failure of these vaccines to provide protection against serovar 15 may be due to novel virulence factors possessed by serovar 15, significant differences between the ApxIII toxin of serovar 15 and those present in the Porcilis APP vaccine or failure by both vaccines to induce antibodies to the serovar 15 specific polysaccharide.