Horse owners need to protect their animals from the West Nile virus, North Dakota State University Extension Service equine specialist Carrie Hammer advises.

Numerous states are reporting an increase in the number of equine West Nile virus cases this year. The U.S. Geological Survey’s disease map reports 157 cases in 31 states as of Aug 28. In contrast, only 119 cases were reported in all of 2011.

Louisiana is the leading state with 26 reported positive cases, while North Dakota ranks fourth with 10 cases.

“Horses become infected with the West Nile virus after being bitten by a mosquito,” Hammer explains. “The virus is not contagious from horse to horse or from horse to humans.”

The virus affects the horse’s brain and spinal cord; thus, depending on the area affected, clinical signs can vary in range and severity. Some of the more common clinical signs include incoordination (especially of the hind limbs), muscle twitching, depression or heightened sensitivity, stumbling, toe dragging, inability to get up and death.

“Unfortunately, approximately 30 percent of horses that show severe clinical signs will die,” Hammer says. “Many horses that survive the initial illness will have residual effects, such as an altered gait or behavior for months.”

No specific treatment is available for horses affected with the virus. Treatment will depend on clinical signs and focuses on controlling pain and reducing inflammation. Owners should consult with their veterinarian immediately if they suspect their horse may have the virus. Prompt and early treatment often can minimize the severity of the disease.

The American Association of Equine Practitioners (AAEP) lists the following guidelines to help protect your horse against the West Nile virus:

• Vaccinate your horse. The AAEP vaccination guidelines are available at http://www.aaep.org/wnv.htm. Horse owners should talk with their veterinarian to ensure their animals are vaccinated properly against the virus.
• Eliminate mosquito-breeding sites (old tires and other containers that hold standing water).
• Use larvicides when eliminating certain mosquito breeding sites is not possible. Be sure to consult with your local Extension agent or mosquito control authority before taking this action.
• Clean water troughs at least monthly.
• Keep your horse indoors during peak mosquito activity periods (dusk to dawn) if possible.
• Install fans over horses (mosquitos have trouble flying against the wind).
• Avoid turning on lights in the barn during the evening.
• Use insect repellants and/or fly sheets and masks that are designed to repel mosquitos.

“Many horse owners have stopped vaccinating against the West Nile virus because the number of cases has been low in recent years,” Hammer says. “This year is a reminder that the virus is still here and should not be forgotten.”

NDSU Agriculture Communication - Aug. 30, 2012