Real-time PCR quantification and histopathological findings of Mycoplasma hyopneumoniae infection in the lungs of pigs slaughtered in São Luís, Maranhão, Brazil

ABSTRACT: Porcine enzootic pneumonia (PES), mainly caused by the bacteria Mycoplasma hyopneumoniae, is the main cause of respiratory problems in pigs. Infection by M. hyopneumoniae leads to production losses and the predisposition of affected animals to secondary infections, which may result in the condemnation of carcasses and organs due to lung lesions at the time of slaughter. The objective of the research was to evaluate the infection by M. hyopneumoniae in pigs submitted to slaughter in São Luís Island/MA, using molecular and histopathological diagnostic methods. One hundred fifty lung samples were collected from inspected (n=65) and non-inspected (n=85) slaughter pigs on São Luís Island, Maranhão, from July 2019 to August 2021. Of the 150 DNA samples collected, 121 showed an amplified product for Cyt B in the PCR assay. Thus, 121 samples were submitted to qPCR of M. hyopneumoniae, of which 44 (36.36%) showed positive results. The mean amount of bacterial load ranged from 1.20 × 101 to 7.20 × 104, with a mean of 1.73 × 104 copies. Of the reagent samples, 81.81% (36 samples) were obtained from non-inspected slaughter, while 18.18% (8 samples) were obtained from slaughterhouses. In the histopathological analysis, 44 positive qPCR samples were evaluated, of which 28 (63.63%) presented results compatible with the main inflammatory process associated with the presence of M. hyopneumoniae, that is, bronchial-associated lymphoid tissue hyperplasia (BALT). Three samples that showed the highest bacterial load (qPCR: 5.63 × 10³, 2.19 × 104 and 7.23 × 104) showed more evident lesions in this study. The microscopic findings associated with the quantifications indicated a relationship between the amount of bacterial load and the presence of microscopic lesions; higher bacterial load in lung tissue is associated with increased histopathologic staining for BALT hyperplasia. In conclusion, the results point to the circulation of the etiological agent in the sampled animals and the need for preventive measures on pig farms in Maranhão with the involvement of producers, sanitary defense and inspection agencies.