Optic Neuritis and Pyogranulomatous Encephalitis Caused by West Nile Virus in an Aged Mountain Lion (Puma concolor aztecus)
A 16-year-old mountain lion (Puma concolor aztecus) with a history of chronic renal failure presented with signs of disorientation, lethargy, and impaired vision. Over the course of the next 24 hours the animal exhibited signs of incoordination, circling to the left, bumping into walls, and bilateral mydriasis. Diagnostic evaluation included a complete ocular examination, a magnetic resonance brain scan, cerebral spinal fluid analysis (with anaerobic, aerobic, and fungal cultures), complete blood count, serum chemistry, and serology (feline infectious peritonitis, canine distemper, West Nile virus, St. Louis encephalitis, and coccidiodomycosis). The animal was treated supportively with antibiotics, steroids and fluids as needed. Significant findings by the neurologist were a bilateral optic neuritis, pyogranulomatous encephalitis, and an elevated WNV titer [1:640 by hemagglutination inhibition (HI)].
The animal recovered over the course of 1 month and remained clinically normal for 11 weeks except for impaired vision that developed after corticosteroids were discontinued. Over the next several months the animal intermittently exhibited episodes of ataxia, lethargy, circling, disorientation, nystagmus, bilateral mydriasis, bumping into walls, muscle tremors, and a possible seizure. The animal responded to steroids with or without antibiotics.
Mosquito trapping in the area at the time of the initial signs showed no evidence of WNV infected mosquitoes; although, in an adjacent enclosure, a male pronghorn was diagnosed with a WNV infection 1 month prior to the mountain lion’s infection.