CORRELATION BETWEEN PREDISPOSING FACTORS AND LUNG INFLAMMATORY LESIONS IN PIGS INFECTED NATURALLY WITH MYCOPLASMA HYOPNEUMONIAE

Introduction: Mycoplasma hyopneumoniae and several predisposing factors are involved in the pathogenesis of enzootic pneumonia. The aim of this study was to investigate the correlation between farm management factors and pulmonary alterations in slaughtered swine. Materials and Methods: Lungs (n 5 1,103) from fattened pigs from 18 different vaccinated and unvaccinated batches from Italian herds were examined macroscopically. For each slaughtered batch, data related to production system, management practices and vaccination protocols were collected. One-hundred lung tissue samples were fixed in formalin and zinc salts for histopathological and immunohistochemistry studies (using antibodies against CD3, CD79 and Iba1). Results: Open cycle, growingefinishing weight !30 kg, presence of slatted systems and mixed natural and forced ventilation systems are predisposing factors. The histopathological investigation revealed that vaccinated animals had less severe lung lesions and more evident BALT hyperplasia. In vaccinated animals not affected by pneumonia, a higher count of B and T lymphocytes and a lower number of macrophages were observed in the BALT compared with unvaccinated animals. In vaccinated animals with pneumonia, a higher number of T lymphocytes and macrophages and fewer B lymphocytes were evident in BALT and in interalveolar septa than in unvaccinated animals. Conclusions: The study defined the main risk factors involved in the pathogenesis of enzootic pneumonia. A good tissue immune response was evident in vaccinated pigs without lung lesions, but a lower Th2 response and a higher non-protective cell-mediated response was observed in vaccinated animals with pneumonia.