Infectious Disease Alert- West Nile Virus

Hagyard Equine Medical Institute’s McGee Medicine Center has diagnosed the first case of WEST NILE in the state in an 8-year-old Thoroughbred pregnant mare located in Woodford County. The mare had been vaccinated for West Nile in January earlier this year.

Symptoms: The mare presented with a 103F degree fever and depression as the initial signs. Hours later she started to have muscle fasciculations and ataxia and was referred to the hospital.

Patient: Recovering and 50% improved

Recommendations: It’s been the perfect year for mosquitos due to the wet environment. In previous years, West Nile Virus have been diagnosed in patients who were vaccinated in January/February. Discuss with your veterinarian if your horse may need to have another booster.

About West Nile Virus: It is a mosquito borne Flavivirus infectious disease with humans and horses as dead-end hosts. Clinical signs, which can be sudden and progressive, include the following:

• ataxia and weakness

• fevers (101F-103F)

• periods of hyperexcitability to listlessness/depression

• fasciculations of face/neck/shoulder muscles, hyperesthesia, complete flaccid paralysis of one or more limbs

• potential development of recumbency rapidly with complete flaccid paralysis of one or more limbs

Diagnosis: Serology (a blood test) looks at a specific antibody called IgM. We use this for acute cases because the current vaccines do not elicit an IgM response. This test can be performed at the University of Kentucky Veterinary Diagnostic Laboratory

How the virus causes disease: The virus causes Polioencephalomyelitis, primarily affecting the brain (diencephalon). The virus will then progress through the hind brain, and frequently throughout the spinal cord. This can lead to an increase release of excitatory neurotransmitters that results in the muscle fasciculations and ataxia.