Meningoencephalitis secondary to rhinitis caused by Pythium insidiosum in sheep

ABSTRACT: A case of meningoencephalitis caused by Pythium insidiosum secondary to rhinitis is reported in a three-year-old crossbred sheep from a herd of 15 animals, raised extensively and with free access to a weir. The animal presented mild dyspnea, blindness, mydriasis, opisthotonos, nystagmus, incoordination, decreased mandibular tone, and spasticity of the pelvic limbs. Macroscopic examination of the nasal cavity showed a blackish-red, irregular, friable mass that bilaterally compromised the nasal septum and the rostral portion of the nasal turbinates. In the brain, there was diffuse thickening of the leptomeninges of the cerebellum and ventral portion of the brainstem characterized by yellowish, granular material associated with vessel hyperemia. On the floor of the fourth ventricle, there was deposition of yellowish, irregular, slightly granular material that protruded towards the obex and displaced the cerebellum dorsolaterally. Microscopically, there were pyogranulomatous, eosinophilic, necrotizing rhinitis and fibrinosuppurative, eosinophilic, necrotizing meningoencephalitis, both associated with thrombosis, vasculitis, and intralesional hyphae. The hyphae were impregnated with silver and presented thin, parallel walls, rarely septate and branched. At immunohistochemistry, the hyphae were immunostained with polyclonal anti-P. insidiosum antibody in fragments of the cerebellum and nasal cavity. The findings showed that P. insidiosum rhinitis can secondarily affect the nervous system of sheep, causing nonspecific neurological clinical signs.