Pathomorphological and microbiological diagnosis of pneumonia due to Pasteurella multocida and associated agents in goats of Punjab, India.

The study investigated the incidence of respiratory infections caused by Pasteurella multocida in goats, both as a primary pathogen and in co-infections. Twenty-four goat carcasses submitted for necropsy between January 2024 and March 2025 to the Department of Veterinary Pathology, Guru Angad Dev Veterinary and Animal Sciences University, Ludhiana, were examined. Diagnosis was based on gross and histopathology and confirmed using immunohistochemistry (IHC), microbial isolation, and PCR.Pasteurella multocida was detected in 14 of 24 cases. In 4 of these, it was the sole pathogen producing fibrinopurulent bronchopneumonia. In the remaining 10 cases, it occurred as a co-infection with Staphylococcus aureus, Escherichia coli, or Streptococci, leading to broncho-interstitial pneumonia. Gross lesions in Pasteurella pneumonia included pleural adhesions, fibrinous pleuritis, and pulmonary consolidation. Histologically, oat-shaped macrophages, fibrin deposition, and pleural thickening were characteristic. IHC demonstrated P. multocida antigen in bronchiolar epithelium and pneumocytes, which was further confirmed by PCR targeting the KMT1 gene.Co-infection cases showed mild to moderate fibrinous pleuritis, sometimes with abscessation. Histopathology revealed thickened interalveolar septa due to lymphocytic, macrophagic, and neutrophilic infiltration, epithelial sloughing, necrotic debris, and inflammatory exudate within bronchi and bronchioles, with multifocal to coalescing abscesses. Bacteriological isolation confirmed S. aureus, E. coli, and Streptococci, while IHC and PCR targeting the nuc gene confirmed S. aureus.The study concludes that P. multocida alone produces fibrinopurulent bronchopneumonia, whereas mixed infections result in a broncho-interstitial pattern of pneumonia in goats.