Fatal hepatic sarcocystosis in a puppy with eosinophilia and eosinophilic peritoneal effusion

A 3-month-old male Golden Retriever puppy was evaluated for lethargy and fever of 2-days duration. Results of a CBC and biochemical profile revealed marked eosinophilia (6.3 X 10(3)/microL; reference interval 0.1-1.2 X 10(3)/microL), moderate thrombocytopenia, and increased activities of alanine aminotransferase, aspartate aminotransferase, and creatine kinase. Hepatomegaly and peritoneal effusion were found using abdominal ultrasound. Peritoneal fluid analysis revealed eosinophilic inflammation (23,000 nucleated cells/microL with 88% eosinophils). Despite supportive treatment the puppy's condition deteriorated rapidly; euthanasia was requested, and a necropsy performed. Microscopically, there was marked necrosuppurative and eosinophilic hepatitis with vasculitis. Numerous hepatocytes contained protozoal organisms suspected to be Toxoplasma gondii or Neospora caninum. However, serum was negative for both T gondii and N caninum antibodies; polymerase chain reaction assay on hepatic tissue was negative for both organisms; and immunohistochemical evaluation of hepatic tissue using serum raised against T gondii, N caninum, and Sarcocystis neurona also was negative. Schizont morphology suggested that merozoites replicated by endopolygeny, forming rosettes around a central residual body. Transmission electron microscopy revealed that merozoites lacked rhoptries. These findings were consistent with a diagnosis of Sarcocystis canis, an apicomplexan parasite with an unknown life cycle.