Establishment of a model of Mycoplasma hyopneumoniae infection using Bama miniature pigs

Abstract

Mycoplasma hyopneumoniae (M. hyopneumoniae), is the primary aetiological agent of enzootic pneumonia leading to chronic respiratory disease prevalent worldwide. Conventional pigs are the only animals used for pathogenicity studies and vaccine evaluations of M. hyopneumoniae. Considering that the challenge animals have better genetic stability and a smaller body size to operate with, an alternative experimental animal model of M. hyopneumoniae infection with Bama miniature pigs was established. Nine seven-week-old snatch-farrowed, porcine colostrum-deprived (SF-pCD) Bama miniature pigs and nine conventional pigs were randomly divided into two infected groups (Bama miniature-infected (BI) and conventional-infected groups (CI), BI and CI, n = 6) and two control groups (Bama miniature control (BC) and conventional control (CC) groups, BC and CC, n = 3). Every piglet was tracheally inoculated with 5 × 108 CCU/mL containing 10% suspension of a stock of frozen lung homogenate from SF-pCD pigs infected with virulent strain JS or sterilized KM2 medium. Typical lung lesions appeared in all infected pigs after necropsy, and the mean gross lung lesions was 17.3 and 13.7 in groups of BI and CI. Serum IgG and nasal sIgA antibody titres were increased significantly. Cilia shedding and mucus staining increased greatly in JS-infected bronchi. Obvious reddish gross lesions and M. hyopneumoniae antigen were detected, especially apparently observed in group of BI. Moreover, DNA copies of M. hyopneumoniae from bronchoalveolar lavage fluid (BALF) of each JS-infected piglet reached more than 108, and M. hyopneumoniae could be re-isolated from each infected BALF. These results indicate that Bama miniature pigs could be used as an alternative and more maneuverable experimental infection model for M. hyopneumoniae and display typical clinical and pathological features consistent with those in conventional pigs.