Integrated pathological and molecular characterisation of respiratory disease in extensively reared Sicilian Black pigs: detection of Mycoplasma hyopneumoniae, porcine circovirus type 2, and concurrent pulmonary silicosis.

The Sicilian Black pig is a well-adapted autochthonous breed, yet its susceptibility to respiratory disease remains poorly defined due to limited data on pathogen circulation and lesion patterns in extensive production systems. This study characterised the pathological features of Porcine Respiratory Disease Complex (PRDC) in this breed by examining lungs and tracheobronchial lymph nodes from 59 animals through pathological assessment, molecular detection of major respiratory pathogens, and evaluation of crystalline particulates using scanning electron microscopy coupled with energy-dispersive X-ray analysis to characterise infectious and environmental contributors. Gross examination revealed multifocal cranioventral bronchopneumonia in 35/59 pigs (59.32%) and diffuse interstitial pneumonia in 18/59 pigs (30.51%). Molecular testing identified Mycoplasma hyopneumoniae (M. hyopneumoniae) as the most frequent pathogen (17/47; 36.17%), followed by porcine circovirus type 2 (PCV2; 10/47; 21.28%) and Pasteurella multocida (6/47; 12.77%), with co-infections consistently involving M. hyopneumoniae. The presence of pathogen DNA was correlated with increased severity of lesions as well as the presence of fibrosis and hyperplasia of the BALT. Histological evidence of Metastrongylus spp. lungworms was identified in 7/35 pigs (20%) with bronchopneumonia. Silicate crystals consistent with pulmonary silicosis were detected in 10/59 lungs (17.0%), indicating substantial exposure to silicate-rich dust in outdoor environments. However, silicosis was not related to the presence of specific respiratory pathogens. Overall, these findings demonstrate that respiratory disease in Sicilian Black pigs is multifactorial, arising from the combined influence of bacterial, viral, parasitic, and environmental components. The concurrent detection of M. hyopneumoniae, PCV2, secondary bacterial agents, lungworm infestation, and silicate particulates supports an integrated PRDC model in this native breed. These results highlight the need for a multifaceted control strategy, including improved diagnostics, targeted management, immunoprophylaxis, helminth control, and mitigation of silicate-rich dust to reduce the impact of PRDC in extensive production systems.