Septic pericardial effusion with <i>Pasteurella</i> species in an immunosuppressed Cavalier King Charles spaniel

Summary A 4‐year‐old, male, entire Cavalier King Charles spaniel presented for a 3‐day history of lethargy, inappetence and occasional coughing. The patient was being treated with prednisone and cyclosporine for lymphoplasmacytic and eosinophilic enteritis diagnosed 2months prior. Clinical pathology revealed a significant leukocytosis, a mild non‐regenerative anaemia, and moderate hypoalbuminaemia. Point‐of‐care thoracic ultrasonography revealed pericardial effusion. Subsequent therapeutic pericardiocentesis resulted in improved cardiac output. Immunosuppressant therapy was discontinued, and supportive therapy was instituted. However, the dog rapidly deteriorated over 12 hours despite no evidence of pericardial effusion reaccumulation. The dog experienced respiratory arrest and, despite initial successful resuscitation, was ultimately euthanased. Laboratory cytological analysis of the pericardial fluid was consistent with septic pericardial effusion, with culture revealing growth of Pasteurella species. Opportunistic pericardial infection of an unreported bacterium secondary to immunosuppressive therapy was considered the most likely cause of septic pericarditis in this case. An underlying immunodeficiency was also suspected.