Sarcocystis neurona encephalitis in a dog.

Summary

# Editorial Summary: Sarcocystis neurona encephalitis in a dog Whilst *Sarcocystis neurona* is well-established as a cause of neurological disease in horses, its occurrence in other species remains poorly documented; this case report describes the first confirmed diagnosis of *S. neurona* encephalitis in a canine patient. A 1.5-year-old male dog presenting with hind limb paresis that progressed despite corticosteroid treatment (dexamethasone) to recumbency, hyperaesthesia, and behavioural changes was found at post-mortem examination to have multifocal encephalitis predominantly affecting the cerebellum and cerebrum, with protozoan organisms identified at sites of inflammation and tissue necrosis. Immunohistochemistry using species-specific polyclonal and monoclonal antibodies, combined with polymerase chain reaction confirmation, definitively identified *S. neurona* as the causative agent, whilst negative testing for *Toxoplasma gondii* and *Neospora caninum* ruled out other protozoal differentials. This case extends the known host range for *S. neurona* beyond equines and highlights the zoonotic potential and epidemiological complexity of this parasite; equine professionals should be aware that clinical neurological signs in dogs with poor response to standard treatment warrant investigation for *S. neurona*, particularly in endemic regions, and that shared environmental exposure pathways between horses and other domestic species merit further investigation.

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Key Findings

• •Sarcocystis neurona encephalitis was identified for the first time in a dog, confirmed by immunohistochemistry and PCR
• •Multiple foci of encephalitis were present in the cerebrum and cerebellum with associated malacia and protozoan organisms
• •Dexamethasone treatment provided initial favorable response but posterior paresis returned and progressed to recumbency

Conditions Studied