Unusual pulmonary thromboembolism in a Dirofilaria immitis infected dog

The nematode Dirofilaria immitis and its endosymbiont Wolbachia are the agents of canine heartworm (HW) disease. The worm´s main habitats are the pulmonary arteries, which elicit inflammation and disorders of the coagulation process. Clinical signs vary according to multiple factors, including worm burden, individual reaction, and duration of infection. This report describes an unusual case of pulmonary thromboembolism secondary to HW infection. A 7-year-old female dachshund presented with a history of cough, dyspnea, and two syncope episodes. On physical examination, the oral mucosa was slightly discolored, the femoral pulse was weak, respiratory distress was present, and the abdomen distended. Echocardiography showed severe right atrioventricular and pulmonary artery enlargement and a large structure with high echogenicity in the artery. After the dog died naturally, the lungs and heart were examined. Only one worm was found in the right ventricle, and a large thrombus was found in the main pulmonary artery. Histologically, fibrin thrombi and fragments of parasites were present inside the pulmonary artery branches. These findings highlight the importance of a thorough clinical evaluation of HW patients and confirm that only a few worms can threaten an animal’s life. Therefore, veterinarians must enforce chemoprophylaxis once treatment is life threatening.