Development of a live oral vaccine against porcine enzootic pneumonia

Mycoplasma hyopneumoniae is the etiological agent of porcine enzootic pneumonia, a commercially expensive respiratory disease of swine. Currently there are no easily administered, cost effective vaccines against this pathogen. The development of efficacious recombinant subunit vaccines would aid greatly in ameliorating economic losses incurred in the pig meat industry as a consequence of enzootic pneumonia. As part of a program aimed at identifying protective antigens of Mycoplasma hyopneumoniae, a random pEX library was constructed and screened with antisera from hyperimmunised pigs. One clone (pSD9), identified by Dr S.P. Djordjevic, contained a 0.8 kb M. hyopneumoniae DNA fragment which encodes an immunoreactive antigen of that pathogen. This antigen was expressed as an 11 kDa M. hyopneumoniae component fused to the carboxy-terminus of the 117 kDa pgalactosidase protein to produce a 128 kDa fusion protein. Antibodies generated in rabbits against the 128 kDa fusion protein reacted in immunoblots against a 42 kDa protein of M hyopneumoniae. The vaccine potential of purified fusion protein was assessed in pig vaccine trials by delivery of the antigen emulsified in different adjuvant formulations. Following experimental challenge with virulent M. hyopneumoniae, the mean Goodwin lung score of all vaccinated animals, irrespective of the adjuvant treatment, was significantly reduced compared to control unvaccinated pigs (P < 0.05) (performed by staff at the Elizabeth Macarthur Agricultural Institute).