Actinobacillus pleuropneumoniae, Actinobacillus suis, and Haemophilus parasuis are upper respiratory residing pathogens, which cause fatal respiratory illnesses, meningitis, and septicaemia in pigs. Prevention through immunizations is key, however, prevention based on vaccination is a major concern due to the limited cross protection conferred by the inactivated whole cell vaccines currently used. These pathogens rely on surface transferrin-binding proteins A and B (TbpA and TbpB) for acquiring iron from the host iron-binding protein transferrin, a process essential for survival and causing disease. Based on our diversity analysis of TbpBs from many strains of the three pathogens we believe that a single vaccine based on a limited number of diversity representative TbpB based antigens will be capable of inducing a cross protective immune response against all three pathogens.
We have demonstrated that immunizations of pigs with a recombinant form of TbpB defective in binding transferrin, Y167A-TbpB, provides superior protection against infection by H. parasuis Nagasaki str. compared to the wildtype TbpB. Furthermore, we have shown this protection to be both homologous and cross protective. Recently, we evaluated the ability of different vaccine formulations and administration routes based on the mutant Y167A-TbpB against a homologous H. parasuis challenge in a conventional pig model. The vaccines were all immunogenic in pigs, however, differences in terms of antigenicity, immune response, and clinical symptoms were observed. We observed that some vaccines not only prevented infection but also appeared to eliminate natural colonization by H. parasuis during the experiment. In conjunction with previous studies, our results demonstrate that the Y167A-TbpB antigen is a promising antigen for developing a broad-spectrum vaccine against H. parasuis infection and colonization and brings us closer to identifying the limited set of TbpB based antigens that will be capable of inducing a cross-protective response against all three pathogens.