Actinobacillus pleuropneumoniae (A. pleuropneumoniae), the causative agent of porcine contagious pleuropneumonia (PCP), is a significant pathogen of the world pig industry, vaccination is potentially an effective tool for the prevention of PCP. The purpose of present study was to enhance the immunogenicity of A. pleuropneumoniae live vaccine strain HB04C- (serovar 7), which was unable to express ApxIA, and to develop effective multivalent vaccines for the respiratory pathogens based on the attenuated A. pleuropneumoniae. We introduced a shuttle vector containing intact apxIA gene into HB04C-, generating HB04C2, an A. pleuropneumoniae serovar 7 live attenuated vaccine strain co-expressing ApxIA. Then we investigated the biological characteristics of HB04C2. We found that the shuttle vector expressing ApxIA was stable in HB04C2, and the growth ability of HB04C2 was not affected by the shuttle vector. We observed that HB04C2 elicited detectable antibodies against ApxIA and ApxIIA when it was administrated intratracheally as a live vaccine in pigs, and all immunized pigs were protected from heterologous virulent A. pleuropneumoniae (serovar 1) challenge. In conclusion, we demonstrated that A. pleuropneumoniae live vaccine could be used as a vector for expression of heterologous antigens.
Actinobacillus Infections ; prevention & control ; veterinary ; Actinobacillus pleuropneumoniae ; classification ; immunology ; Animals ; Bacterial Proteins ; biosynthesis ; genetics ; Bacterial Vaccines ; biosynthesis ; immunology ; Hemolysin Proteins ; biosynthesis ; genetics ; Pleuropneumonia ; microbiology ; prevention & control ; Swine ; Swine Diseases ; microbiology ; prevention & control ; Vaccines, Attenuated ; biosynthesis ; immunology

Swine respiratory diseases induce severe economic losses in the swine industry worldwide. Several methods have been developed and applied to control these diseases. However, there are still problems of disease control in the swine industry. Recently, egg yolk antibodies have been found to offer several advantages for disease control in animals and humans. In a previous study (24), antibodies to several causative pathogens of swine respiratory diseases were developed. However, several problems remained, especially in terms of reduced laying rates. Therefore, experimental vaccines were reformulated with various bacterial antigens of the swine respiratory diseases. After immunizing hens with the antigens, antibody profiles and other effects including laying rates were investigated and compared to those of the previous study. Profiles of antibody titers were very similar with those of the previous study. However, side effects, such as depression, weakness, reduction of laying rates and mortality, were dramatically lowered and laying rates were increased in hens injected with certain experimental vaccines. In particular, laying rates of hens injected with vaccines against atrophic rhinitis were increased up to 84% by injecting a vaccine composed of only the DNTs of B. bronchiseptica and P. multocida D:4. Efficacies of the vaccines against swine pneumonic pasteurellosis and pleuropneumonia were very similar with those of the previous study. These results suggest that new vaccines could be effective in the production of egg yolk antibodies against the causative agents of swine respiratory diseases.
Actinobacillus pleuropneumoniae/classification/genetics/*immunology ; Animals ; Antibodies, Bacterial ; Antibody Formation ; Bacterial Outer Membrane Proteins/genetics/isolation & purification ; Bordetella bronchiseptica/classification/genetics/*immunology ; Egg Yolk/microbiology ; Female ; Immunoglobulins/*genetics ; Oviposition ; Pasteurella multocida/classification/genetics/*immunology ; Serotyping ; Swine