Efficacy of a Mycoplasma hyopneumoniae bacterin in pigs challenged with two contemporary pathogenic isolates of M hyopneumoniae

Objective: To evaluate the efficacy of a Mycoplasma hyopneumoniae (M hyo) bacterin against two contemporary field isolates of M hyo. Materials and methods: Two challenge studies were performed in which pigs received two doses of either saline (nonvaccinated groups) or an M hyo bacterin (vaccinated groups), followed 3 weeks later by intratra-cheal inoculation of each pig with one of two M hyo field isolates. Necropsies were performed 28 or 30 days post challenge. Vaccine efficacy was determined by evaluating macroscopic lung lesions, DNA levels of M hyo in bronchial alveolar lavage fluids (BALF), M hyo-specific immunoglobulin (Ig)A and IgG antibodies, and serum antibodies measured by the Tween 20 and DAKO enzyme-linked immunosorbent assays. Results: The percentage of macroscopic lung lesions and concentration of M hyo DNA in BALF samples post challenge with either isolate were significantly less in vaccinated than in nonvaccinated pigs (P < .05). M hyo-specific mucosal IgA and IgG antibody levels in BALF were significantly higher in the vaccinated pigs than in the nonvaccinated Pigs-Implications: Under the conditions of these studies, fewer M hyo organisms and fewer macroscopic lesions of pneumonia are observed when pigs are vaccinated with an M hyo bacterin prior to challenge with contemporary virulent M hyo field isolates. Vaccination is an effective tool to reduce pneumonia induced by M hyo. although more studies are needed to determine protection against a wide range of field isolates.