An evaluation of the role of antibodies toActinobacillus pleuropneumoniaeserovar 1 and 15 in the protection provided by sub‐unit and live streptomycin‐dependent pleuropneumonia vaccines

Abstract

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 serovarspecific 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.

Adhesion Protein ApfA of Actinobacillus pleuropneumoniae Is Required for Pathogenesis and Is a Potential Target for Vaccine Development

“…Since each of the Apx exotoxins confers only partial protection against porcine pleuropneumonia and the distribution of Apx exotoxins varies among the different serotypes, the current commercial vaccine (Porcilis APP, Intervet, Holland) is composed of three toxoids-ApxI, ApxII, and ApxIII-and one 42-kDa outer membrane protein. This subunit vaccine is effective at preventing acute disease, but it neither protects effectively against colonization nor confers cross-serotype protection (8).…”

Efficacy Evaluation of Combination Vaccine of Recombinant C-Terminal Fragments of ApxIA, ApxIIA and ApxIIIA in Piglets

“…These vaccines do not effectively prevent colonization and are not widely cross protective (Tumamao et al 2004). As other pathogenic bacteria of multiple serotypes, a major point in the prevention of APP infections is to identify conserved antigens or proteins involved in immunogenicity, which may provide cross-protection against distinct APP serotype infections (Chen et al 2012;Haesebrouck et al 2004).…”

“…Various studies have been carried out to identify vaccine candidates for efficient cross-protection, such as killed bacterin vaccines and subunit vaccines (Blackall et al 2002;Haesebrouck et al 2004;Zhou et al 2013). These vaccine candidates do not prevent colonization and are not widely cross-protective (Tumamao et al 2004). Therefore, further efforts need to be made for development of more efficient vaccines.…”

Genetic and antigenic characteristics of ApxIIA and ApxIIIA fromActinobacillus pleuropneumoniaeserovars 2, 3, 4, 6, 8 and 15

“…Recently, commercially available toxin‐type vaccines have been shown to confer strong protection against a wide variety of A. pleuropneumoniae serovars. However, a recent trial with one of these vaccines, composed of ApxI, ApxII, ApxIII and a 42 kDa outer membrane protein, showed that the vaccine failed to protect swine against challenge with strain HS143 (serovar 15) . The failure of this toxin‐type vaccine may be attributable to differences between the ApxII and ApxIII toxins and specific polysaccharide of serovar 15 and those incorporated in the vaccines .…”