Horse identified with West Nile Virus in northwest Oklahoma  

Horses not infected with West Nile Virus. (Journal stock photo.)

According to the Equine Disease Communication Center website at, another horse in Oklahoma is suffering from the effect of West Nile Virus. 

On Nov. 7, a yearling Quarter Horse stallion started showing clinical signs of the disease Oct. 29, with hindlimb weakness. The horse is recovering and was unvaccinated. Another horse was reported in Ottawa County Nov. 6. 

Since Aug. 1, there have been 15 horses identified by the Oklahoma State Veterinary Office and reported on the EDCC website. Counties with affected horses include Caddo, Carter, Cherokee (2), Coal, Harper, Hughes, Jackson, Oklahoma, Ottawa (2), Pawnee, Payne, Washita, and Woodward. 

Of those identified, ages range from yearling to 10 years old, and some ages are unknown. Several were vaccinated, most unvaccinated and a few had unknown vaccination status. 

According to the EDCC, West Nile Virus is a mosquito-borne flavivirus. WNV primarily causes disease in birds, humans, and horses and is transmitted by many different species of mosquitoes. Since 1999, more than 27,600 United States horses have been confirmed with WNV neuro-invasive disease with an estimated average case fatality rate of 30% to 40%. During 2002 alone, over 15,000 horses were affected in the U.S. WNV is now considered endemic with yearly activity in the U.S. (with an average 300 cases per year), Canada, Mexico and the Caribbean. 

Clinical signs include: 

• Depression and anorexia without fever when initially infected; 

• Mild low-grade fever (101.5 to 103.5 degrees Fahrenheit or 38.6 to 39.7 degrees Celsius) in about 25% of affected horses; 

• Lack of appetite; 

• Lethargy or drowsiness; 

• Neurologic signs (frequently sudden and progressive); 

• Periods of hyperexcitability, apprehension or drowsiness; 

• Fine tremors and fasciculations of the face and neck muscles 

• Cranial nerve paralysis (facial paralysis and tongue weakness common); 

• Head tilt, droopy lip, muzzle deviation; 

• Weakness, ataxia, and dysmetria (incoordination) in one or all limbs; 

• Complete paralysis of one or more limbs; 

• Colic; 

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• Recumbency, the inability to stand; and • Death. 

For more information on WNV or see other states with cases, visit

Kylene Scott can be reached at 620-227-1804 or [email protected]