Treatment failure in a dog with acute Babesia canis infection using lower-range therapeutic doses of imidocarb dipropionate.

Canine babesiosis caused by Babesia canis is considered an emerging disease in Central and Eastern European countries, including Germany. Imidocarb dipropionate is recommended for treatment of acute B. canis infections. A nine-year-old, male intact Golden Retriever living in Saxony, Germany, was presented in November 2025 due to lethargy, inappetence, vomiting, fever (39.6 °C), and darkened urine to a small animal veterinary practice. Ectoparasite prophylaxis was discontinued three months before the onset of clinical signs. An acute B. canis infection was diagnosed based on microscopic detection of large merozoites in peripheral blood smears, followed by Babesia spp. PCR and sequencing. Hematological examination revealed marked thrombocytopenia, mild non-regenerative anemia, lymphopenia, and eosinopenia. The dog remained PCR positive after two imidocarb dipropionate injections (2.0 mg/kg bodyweight and 5.0 mg/kg bodyweight s.c.), and hematological abnormalities were still present. Prednisolone (2.0 mg/kg bodyweight s.c., continued orally) was applied, after which merozoites were still detected in peripheral blood smear analysis, so prednisolone was discontinued. After two further imidocarb dipropionate injections (9.4 mg/kg bodyweight s.c. each), the dog presented as clinically healthy, and a subsequent PCR testing was negative. From this report, different measures for dogs suffering from an acute B. canis infections can be derived: Dogs should be treated with a high dosage of imidocarb dipropionate of 6.6 mg/kg bodyweight as approved by the FDA, and the treatment success should be monitored by PCR 14 days post treatment. If treatment fails after two administrations at either dose of imidocarb dipropionate, i.e. if PCR remains positive, it is recommended to verify a B. canis infection by molecular species differentiation, e.g. via sequencing. Furthermore, dogs with treatment failure should be screened for coinfections and underlying comorbidities, which may complicate the course of an acute B. canis infection. Due to the authors’ personal experience, application of corticosteroids, even in non-immunosuppressive dosages, should be avoided, especially if blood transfusions are not necessary and/or marked hemolytic anemia is absent. Furthermore, this report highlights the importance of efficient year-round tick control, even in winter months.