West Nile Virus information for Michigan horse owners

Michigan horse owners need to be aware of West Nile virus and the precautionary measures they can take to help protect their horses now that the virus has been detected in Michigan.

The risk of horses contracting West Nile virus or developing severe disease is very low but it is critical that Michigan horse owners know about the disease and follow some basic but important steps to protect their horses. Reducing mosquito exposure is key in protecting Animals.

West Nile virus was first identified in Michigan at the end of August 2001. To date, 65 crows and blue jays have been confirmed positive with the disease in Wayne, Oakland, Macomb, Ingham, Jackson, Washtenaw, Barry, Calhoun, Ottawa and Muskegon counties. Aggressive surveillance is ongoing, and it has NOT yet been detected in humans or horses. It has been confirmed in one sample of mosquitoes from Oakland County and one sample from Macomb County. These positive mosquitoes were of the Culex pipiens species, which almost exclusively bite only birds. The testing on mosquito species that bite both horses and humans as well as birds, the so called "cross-over" species, has been negative to date.

West Nile virus infects birds, which then serve as the reservoir for the virus. At least 76 species of birds have been shown to be capable of carrying the virus. In the United States, the most common bird seems to be the American Crow, which frequently dies from the infection. Many other species survive infection with mild or no indication of disease.

WNV is spread from bird to bird by mosquitoes. Mosquitoes are also capable of spreading the virus to horses, humans, and other mammals. Most horses bitten by carrier mosquitoes do not develop disease. Of those that do, only about one-third develop severe disease and die, or are so affected that they require euthanasia. Incubation appears to be seven to 14 days.

The virus is NOT transmitted from person-to-person, horse-to-horse or horse-to-person. You cannot get the virus from touching or kissing a person who has the disease, from a health care worker who has treated someone with the disease or from contact with an infected horse.

Clinical signs of West Nile vary in horses, though typical symptoms include ataxia (incoordination, stumbling, limb weakness) that either appears suddenly or appears gradually and worsens, somnolence (sleepiness), dullness, listlessness, facial paralysis (droopy eyelids, lower lip), and the inability to rise. Some horses may also develop mild fevers, blindness, muscle trembling and other signs.

A vaccine is available as an aid to prevent West Nile virus in horses. While the product has been shown safe for use, its effectiveness has not yet been proven. Horse owners should contact their private veterinarian to discuss vaccination and other preventive measures.

MDA and MSU recommend the following measures to lower West Nile virus risk for horses:

• Contact private veterinarian to discuss vaccination.
• Use approved insect repellants to protect horses.
• Place horses in barns/stables under fans during prime mosquito exposure hours of dusk and dawn.
• Eliminate opportunities for mosquito breeding by draining wet areas of pasture, puddles, repairing eave troughs, gutters, and clearing any containers that may hold even small pools of water.
• Drain water tanks once or twice each week.

For more information on West Nile virus and horse surveillance and prevention, contact your local veterinarian or call the state's toll-free West Nile virus hotline at 888-668-0869.

Or take a look at this informative brochure "West Nile Virus in Horses: Diagnosis and Prevention Tips" (PDF file - requires Acrobat Reader)

Michigan has a brand new  West Nile Virus Site representing the collaborative work of several state agencies.

West Nile virus information may also be viewed at the Centers for Disease Control web site at www.cdc.gov