Constrictive-effusive pericarditis and epicarditis as a cause of restrictive cardiomyopathy associated with Dirofilaria repens infection in a dog

A 5-year-old spayed female mixed-breed dog was presented to a veterinary clinic due to progressive generalised weakness and anorexia. Clinical and ultrasound examination revealed the presence of ascites and pericardial effusion. Due to cardiac tamponade, pericardiocentesis was performed, yielding 230 mL of hemorrhagic fluid. Cytological analysis of the fluid revealed the presence of microfilariae. Despite antiparasitic, anti-inflammatory, and supportive therapy, recurrent pericardial effusion and progressive pericardial thickening necessitated thoracoscopic partial pericardiectomy. Pleural effusion developed postoperatively, leading to dyspnea and repeated thoracocentesis. Lack of clinical improvement, along with recurrence of effusions, led the owners to elect euthanasia three months after the initial presentation. Necropsy revealed fibrinous pericarditis and epicarditis, and a single adult Dirofilaria repens in the peritoneal cavity. Histopathological examination confirmed widespread inflammation and fibrosis. D. repens DNA was identified using RT-PCR both in the pericardial fluid ante mortem and in the parasite retrieved from the peritoneal cavity during necropsy. This is the first documented case of pericarditis and epicarditis as a cause of restrictive cardiomyopathy associated with D. repens infection in a dog.