Effect of multiple vaccinations on transmission and degree of Mycoplasma hyopneumoniae infection in gilts

Mycoplasma hyopneumoniae (M. hyopneumoniae) infections continue to result in significant respiratory challenges in the swine industry worldwide. Vaccination for M. hyopneumoniae is commonly utilized, as reduction in bacterial loads and clinical severity in vaccinated pigs have been shown. However, the effect of M. hyopneumoniae vaccination on transmission across different pig populations has been minimally investigated. The aim of this pilot study was to evaluate the effect of multiple vaccinations on M. hyopneumoniae infection, transmission, and genetic variability in infected and susceptible gilt populations. Thirty-two naïve gilts were allocated to four treatment groups: (1) Vaccinated seeder (VS); (2) Non-vaccinated seeder (NVS); (3) Vaccinated contact (VC); and (4) Non-vaccinated contact (NVC). At 5, 7, and 9 weeks of age, all gilts selected to be vaccinated received a commercial M. hyopneumoniae bacterin for a total of 3 doses. At 11 weeks of age, VS and NVS gilts were inoculated with M. hyopneumoniae to become seeders. At 28 days post-inoculation (dpi), VS and NVS gilts were individually relocated to clean experimental rooms, where they were placed in contact with one age-matched VC or NVC gilt (1:1 ratio) for 14 days. Blood and tracheal samples, bronchial swabs, and lung lesions were collected and/or evaluated for M. hyopneumoniae infection. In this study, a three-dose vaccination strategy against M. hyopneumoniae significantly reduced bacterial load in seeder gilts. Furthermore, a numerical reduction in M. hyopneumoniae lung lesions at 28 dpi was observed in VS gilts. All VC gilts in the VS:VC treatment group pairing remained M. hyopneumoniae negative, compared to other groups in which 1–2 transmission events occurred per treatment group. Results from this investigation provide insight on the potential impact of multiple vaccinations on reducing M. hyopneumoniae transmission and infection. Further research encompassing vaccinations of gilt groups in field settings is necessary to validate findings.