In September 2017, Cornell’s Ambulatory Service was called out on emergency to assess a 26 year old Arabian mare with acute onset of muscle fasciculation and ataxia for less than 24 hours. The patient had no history of vaccination.

On presentation, the patient was quiet and alert, but appeared distressed, and was reluctant to move. On physical exam, she was tachycardic, mildly dehydrated, had a stiff gait, and was exhibiting muscle twitching of her muzzle, shoulder, and legs. A neurologic exam was performed, revealing no cranial nerve deficits, pivoting and dragging toes when circled, and reluctance to move when walked with her head raised. The patient became very distressed at this point in the exam and almost fell, so the neurologic exam was stopped.

Possible causes of the acute signs were discussed with the owner at length, ruling out toxins and mineral deficiencies from her feed. Given the time of year, the muscle tremors and the ataxia, the equine encephalitis viruses were prioritized in our differential list and diagnostic plan. The owner agreed to further testing, and blood was collected and submitted for CBC, Chemistry Panel, and West Nile Virus (WNV) Immunoglobulin Titers.

This presentation will discuss equine encephalitis viruses, the statewide prevalence of WNV, and vaccination protocols.