West Nile Virus reported in Michigan horses

Vaccinating your horse for West Nile Virus reduces the risk of your horse getting sick.

The Michigan Department of Agriculture and Rural Development (MDARD) recently received confirmation that three Michigan horses were diagnosed with West Nile Virus (WNV).

Most horse owners are familiar with WNV, which is a virus that affects horses’ neurological system. This virus was first isolated in the United States in New York in the late summer of 1999 and has been a disease of concern ever since.

Transmission of WNV is by mosquitoes. Birds serve as the reservoir host after having been bitten by an infected mosquito. People, horses and other mammals (bats, cats, chipmunks, skunks, squirrels and some domestic rabbits) are incidental hosts and do not spread the disease. Horses can be “dead-end” hosts because they cannot pass this virus to other horses, humans or mosquitoes. However, the virus can be passed from bird to bird only by mosquito bites.

Clinical signs of a horse sick from WNV are: ataxia (incoordination, stumbling, limb weakness), somnolence (sleepiness), dullness, listlessness, facial paralysis (droopy eyelids, lower lip) and inability to rise. Other signs may include: a mild fever, blindness, circling, head pressing, muscle trembling, excitability and seizures. Clinical cases are typically seen between July and October.

There is no specific treatment. Horses that are clinically infected are treated by supportive measures, such as IV fluids, control of fever and safe, quiet housing. Unlike eastern Equine encephalitis (EEE) and Western equine encephalitis (WEE) which have a very low survival rate, WNV clinically affected horses appear to have a 65 percent chance of recovery and return to normal function when treated.

Michigan State University Extension suggests that prevention remains the best practice to follow. One key prevention practice to follow includes vaccinating your horse for WNV. In addition to vaccination, horse owners should protect their horses against mosquitoes by applying repellent, eliminating standing water and bringing horses indoors from early evening until after sunrise when mosquitoes are out in full force.

Unvaccinated horses are at risk, so it’s crucial horse owners work with their veterinarian to make sure their animals are up-to-date on vaccinations. All horses should be vaccinated yearly for WNV, EEE and WEE. It's never too late to vaccinate for these diseases. If your horse’s vaccination history is questionable, work with your veterinarian to determine the best route to providing an adequate protection program in as timely a manner as possible.

If your horse is having any of these symptoms or issues, contact your veterinarian immediately. If your veterinarian suspects WNV or EEE, it should be reported to MDARD at 800-292-3939 (daytime) or 517-373-0440 (after-hour emergencies).

For more information on equine diseases, visit MDARD’s website at www.michigan.gov/equinediseases.

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