Associations between Pleurisy and the Main Bacterial Pathogens of the Porcine Respiratory Diseases Complex (PRDC)

SIMPLE SUMMARY: Respiratory disease is a significant health issue in intensive pig production, and it can have a significant impact on animal welfare, productivity, and profitability. Some of the common respiratory diseases affecting pigs include Porcine Respiratory Diseases Complex (PRDC). These pathogens can act synergistically and cause severe respiratory disease in pigs. Hence, to document and quantify the occurrence of these pathogens, 1015 carcasses of pigs were evaluated according to the pleuritis score in a slaughterhouse. Lungs were evaluated according to the pneumonia index (0.91 to 1.89) and pleurisy score were determined. Samples of lung and pleura were collected for DNA quantification by PCR of these five pathogens in fattening pigs. Moreover, the correlation of bacterial quantification and macroscopic lesions were performed. Our finding revealed a prevalence of 12.3% of pleuritis and correlations between quantification of Actinobacillus pleuropneumoniae, Glaesserella parasuis, Mycoplasma hyopneumoniae, Pasteurella multocida, and Streptococcus suis between different pleurisy scores. Finally, monitoring respiratory lesions in slaughter pigs can provide valuable information about the efficacy of control measures that have been implemented, allowing veterinarians and pig producers to make informed decisions about future management strategies that can lead to improved diagnosis, treatment, and prevention of PRDC. ABSTRACT: Porcine Respiratory Diseases Complex (PRDC) is a multifactorial disease that involves several bacterial pathogens, including Mycoplasma hyopneumoniae (M. hyopneumoniae), Actinobacillus pleuropneumoniae (A. pleuropneumoniae), Pasteurella multocida (P. multocida), Glaesserella parasuis (G. parasuis), and Streptococcus suis (S. suis). In pigs, the infection may cause lesions such pleurisy, which can lead to carcass condemnation. Hence, 1015 carcasses were selected from three different commercial pig farms, where the respiratory conditions were evaluated using slaughterhouse pleurisy evaluation system (SPES) and classified into five groups. In total, 106 pleural and lung fragments were collected for qPCR testing to identify the five abovementioned pathogens. A moderate correlation between the severity of the lesions and the presence of P. multocida (R = 0.38) and A. pleuropneumoniae (R = 0.28) was observed. Concerning the lung samples, the severity of the lesions was moderately correlated with the presence of P. multocida (R = 0.43) and M. hyopneumoniae (R = 0.35). Moreover, there was a strong correlation between the presence of P. multocida and M.hyopneumoniae in the pleura (R = 0.82). Finally, this approach may be a useful tool to identify and quantify causative agents of PRDC using qPCR, providing a comprehensive evaluation of its relevance, strength, and potential application in the field as a surveillance tool for veterinarians.