WNV Reported in Michigan Horse

Michigan's State Veterinarian Dr. Steve Halstead today announced the state's first case of West Nile Virus (WNV) in a horse for 2006. The horse was a 3-year old gelding from Washtenaw County. Dr. Halstead urges residents to take precautions that include preventing mosquito exposure during late summer outdoor activities and vaccinating horses.

The virus is spread by mosquitoes that have fed on wild birds infected with the virus. Many birds are able to harbor the WNV virus without becoming recognizably ill, therefore serving as a reservoir for the disease causing agent. It is important for horse owners to vaccinate their horses to help prevent infection with this potentially deadly virus. Owners should contact their veterinarian for details.

"Michigan typically sees an increase in the number of cases of West Nile Virus this time of year, as the virus, which has been circulating in mosquito and bird populations throughout the spring and early summer, spills over to horses, and potentially humans," said Halstead. "It is imperative that precautions are taken to prevent exposure to mosquitoes."

Most horses bitten by carrier mosquitoes do not develop the 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.

"It is important to note that horses are "dead-end" hosts for West Nile Virus, meaning the disease can't be directly transmitted from infected horses to other horses or humans," added Halstead.

There have been a higher percentage of positive birds in the surveillance testing and an increase in the infection in mosquito samples over the last few weeks. This indicates that the virus infection in mosquito populations is increasing, therefore prevention measures are still very important. Today, the Michigan Department of Community Health (MDCH) also reported its second human case of West Nile Virus. The virus was confirmed in a 36-year-old male in Kent County by the MDCH laboratory in Lansing.

Tips for preventing mosquito-borne sickness in horses include:

  • Vaccinate your horses. Inexpensive vaccines for WNV and related viruses Eastern and Western Equine Encephalitis are readily available. It is not too late to vaccinate horses this season. Talk to your veterinarian for details.
  • Use approved insect repellants to protect horses.
  • If possible, put horses in stables, stalls or barns during the prime mosquito exposure hours of dusk and dawn- under fans if possible to disturb mosquito flight.
  • Eliminate standing water and dense brush, and drain troughs and buckets at least two times a week.

For more information about WNV in horses, contact the Michigan Department of Agriculture, Animal Industry Division, at 517/373-1077, or visit www.michigan.gov/mda. For information on human WNV cases and tips for reducing the risk of becoming infected, contact your local health department or visit the Michigan Department of Community Health Web site at www.michigan.gov/emergingdiseases.

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