Actinobacillus pleuropneumoniae (APP) is a respiratory pathogen which causes severe pleuropneumonia in swine, leading to substantial economic losses in the pig industry. Current vaccines have shown limited protection against APP. The present study aimed to develop and evaluate a septuple-deletion mutant strain of APP (SLW08; serovar 1) as a live attenuated vaccine candidate. The SLW08 was developed from the sextuple-deletion mutant APP WBY06 (ΔapxICΔapxIICΔorf1ΔcpxARΔarcAΔureA) by knocking out ApxIVA and inserting ApxIIIA into the ApxIVA locus. The virulence of mutant strain was assessed in mice. The immunogenicity, safety, and protective efficacy of SLW08 were evaluated in mice and piglets. Protection studies involved challenging immunized and control animals with a virulent APP strain (SLW01) and vaccine efficacy was determined using survival rates and lung pathology. The SLW08 strain exhibited slower growth rates as compared to the WBY06 and WT (SLW01) strains but showed significantly reduced virulence. Vaccinated pigs demonstrated strong immune responses without adverse effects. Upon challenge with virulent APP, the vaccinated pigs showed markedly reduced signs of infection compared to controls, indicating strong protective efficacy. SLW08, expressing ApxIII, provided effective protection to mice and piglets against APP, with less toxicity, resulting in higher survival rates and less lung pathology. The SLW08 mutant of APP with strong immune responses may represent a promising live attenuated vaccine candidate for protecting swine against APP infection.

To Cite This Article: Cao W, He Q, Chen Y, Liu J, Wei Z, Wei X, Chen H and Weicheng Bei, 2024. Development and assessment of a septuple-deletion mutant live attenuated vaccine for Actinobacillus pleuropneumoniae in swine. Pak Vet J, 44(4): 1229-1236. http://dx.doi.org/10.29261/pakvetj/2024.297