First report of a <i>Buchananella hordeovulneris</i> –associated pyothorax in a feline leukaemia virus‐positive cat

Abstract A 10‐month‐old, neutered, male domestic shorthair cat with outdoor access was presented with a thoracic wound, severe respiratory distress, cachexia, dehydration and pleural effusion. Imaging confirmed bilateral pyothorax. Haematology showed marked neutrophilia with left shift, mild anaemia, thrombocytopenia and lymphocytosis. The cat tested FeLV positive and FIV negative. Due to poor prognosis, euthanasia was performed. Necropsy revealed extensive pleural adhesions, abundant exudate, pulmonary and pleural abscesses, pyogranulomatous pleuritis and pericarditis, and fibrinous myocarditis. Histopathology identified pyogranulomatous inflammation surrounding filamentous bacteria in multiple thoracic tissues. Cytology showed abundant neutrophils, pyocytes and filamentous Gram‐positive, non‐acid‐fast bacteria. 16S rRNA sequencing of thoracic fluid and lung confirmed Buchananella hordeovulneris (99.37% identity). This represents the first confirmed report of B. hordeovulneris infection in a cat in Mexico. The case highlights the importance of considering uncommon opportunistic pathogens in feline pyothorax, particularly in immunocompromised patients, and demonstrates the value of combining pathology, cytology and molecular diagnostics.