Successful treatment of a dog with a severe Babesia vulpes infection and associated haemophagocytic syndrome after splenectomy.

A 12-year-old female, neutered, crossbreed dog was diagnosed by its primary care practice with severe Babesia vulpes infection, based on positive PCR testing, three weeks after elective splenectomy for splenic nodules identified on abdominal ultrasound. Despite treatment with standard antiprotozoal therapy, glucocorticoids, and three blood transfusions, anaemia persisted, becoming non-regenerative and prompting referral. Upon presentation, the dog exhibited pale mucous membranes and was hyperthermic. Blood tests revealed a regenerative anaemia, thrombocytopenia, hyperbilirubinaemia, hypertriglyceridaemia, hyperferritinaemia and elevated liver enzyme activity. Coombs' testing was negative, and thoracic and abdominal imaging were unremarkable. A repeated Babesia vulpes PCR was positive and screening for other infectious diseases was negative. Bone marrow cytology and histopathology showed generalised hyperplasia, with macrophages comprising ≥3% of the total nucleated cells. These macrophages displayed prominent erythrophagia and, to a lesser extent, engulfment of mature neutrophils, platelets, and nucleated red blood cells. Therefore, a diagnosis of haemophagocytic syndrome associated with a severe Babesia vulpes infection was made. The dog received double immunosuppressive therapy, a combination of antiprotozoal drugs and a further three blood transfusions. The thrombocytopenia quickly resolved, with the anaemia improving ten days later. The antiprotozoal and immunosuppressive therapies were eventually discontinued without relapse of the babesiosis and repeated Babesia vulpes PCR testing was negative. To the authors' knowledge, this is the first report to describe the successful treatment of a splenectomised dog with severe Babesia vulpes infection complicated by haemophagocytic syndrome.