Acute onset of encephalomyelitis with atypical lesions associated with dual infection of Sarcocystis neurona and Toxoplasma gondii in a dog

•Immunohistochemistry and polymerase chain reaction (PCR) was used to detect Toxoplasma gondii and Sarcocystis neurona in the CNS of a dog with progressive, severe, neurologic impairment and atypical gross lesions.•Banked serum was negative for T. gondii using the modified agglutination test, suggesting an acute case of T. gondii infection or immunosuppression.•To the authors' knowledge, this is the first report of dual T. gondii and S. neurona infection in a dog.

A two-year-old male, neutered, basset hound-beagle mix with progressive neurological impairment was examined postmortem. Grossly, the dog had multiple raised masses on the spinal cord between nerve roots. Microscopically, the dog had protozoal myeloencephalitis. Toxoplasma gondii and Sarcocystis neurona were detected in the CNS by immunohistochemistry and polymerase chain reaction (PCR). Sarcocysts in formalin-fixed muscle were negative for Sarcocystis by PCR. Banked serum was negative for T. gondii using the modified agglutination test, suggesting an acute case of T. gondii infection or immunosuppression; however, no predisposing immunosuppressive diseases, including canine distemper, were found. To the authors' knowledge, this is the first report of dual T. gondii and S. neurona infection in a dog.