August 12, 2004 - A Clinton County horse has tested positive for West Nile virus, the first of the year, veterinary officials with the Michigan Department of Agriculture (MDA) today confirmed.

Laboratory tests conducted in early August at the Michigan State University Diagnostic Center for Population and Animal Health confirmed the presence of West Nile virus (WNV) in the unvaccinated horse, according to Dr. Nancy Frank, Michigan’s Acting State Veterinarian. The horse, which showed signs of stumbling and mild depression, has since recovered from the illness.

The case reaffirms that WNV transmission is occurring in Michigan and the importance of the state’s residents and horse owners remaining on guard against the disease and taking appropriate precautions, Frank said.

“While the risk of horses contracting the virus or developing severe disease is low, it is vital that Michigan horse owners know about WNV and follow some basic, but important, steps to protect their animals,” said Dr. Steve Halstead, MDA Equine Program Manager.

Most horses bitten by carrier mosquitoes do not develop disease. Of those that do, only about one-third develop severe illness and die, or are so affected that they require euthanasia. Clinical signs of WNV in horses vary, though typical symptoms include ataxia (incoordination, stumbling, limb weakness or other unusual movement) that either appears suddenly or appears gradually and worsens, somnolence (sleepiness), dullness, listlessness, facial paralysis (droopy eyelids, lower lip, tongue), and the inability to rise. Some horses may also develop mild fevers, blindness, muscle trembling and other signs.

Halstead said that vaccine products that have been shown safe for use and proven effective are available as an aid to prevent West Nile virus in horses. Horse owners should contact their private veterinarian to discuss vaccination and other preventive measures.

341 Michigan horses tested WNV positive in 2002, prior to widespread awareness and use of vaccine. Only 10 horses tested positive in 2003.

MDA also recommends the following measures to lower WNV risk for horses:

• Eliminating opportunities for mosquito breeding by draining wet areas of pasture, repairing eave troughs, gutters, and clearing any containers, tarps, etc. that may hold even small pools of water.
• Draining and refilling water tanks, troughs or buckets at least weekly.
• Using approved insect repellants to protect horses.
• Placing horses in stables, stalls or barns under fans during the prime mosquito exposure hours of dawn and dusk, and other times when mosquitoes are present, if possible.

For more information on West Nile virus or other arborvirus diseases, plus the latest updates of bird, horse and human cases, visit www.michigan.gov/westnilevirus.