Horse Owners Urged to Watch for West Nile Virus

Extensive rain, flooding, and warm temperatures have created prime conditions for mosquitoes, heightening the risk of the pests transmitting West Nile virus (WNV) and Eastern equine encephalitis (EEE), or "sleeping sickness," to horses. University of Missouri College of Veterinary Medicine (CVM) veterinarians Philip Johnson, BVSc (Hons), MS, Dipl. ACVIM, Dipl. ECEIM, MRCVS, professor of equine medicine and surgery. and Alison LaCarrubba, DVM, Dipl. ABVP, head of the CVM's equine ambulatory section, say horse owners--both in Missouri and elsewhere--should take preventive measures against mosquitoes and vigilantly watch for signs of WNV and EEE from now through October.

"Since WNV was first reported in Missouri in 2001, increased awareness and the availability of effective vaccines have combined to significantly reduce the incidence of the virus among Missouri horses," said Johnson. "However, horse owners need to be extremely cautious this year because the warm, wet weather and extensive flooding increases the risk of WNV spreading."

West Nile virus can cause equine encephalomyelitis, a potentially fatal inflammation of the brain and spinal cord. There were five diagnosed cases of WNV in Missouri in 2010, according to the USDA Animal and Plant Health Inspection Service. However, this is commonly underreported, Johnson said.

Owners should vaccinate their horses against WNV and EEE and booster the vaccinations annually. They should also remove water from flooded pastures or paddocks, water troughs, ornamental water decorations, gutters, and other sources of standing water. They also can utilize commercially available nontoxic water treatment products that kill mosquito larvae.

Though some infected horses do not exhibit clinical signs of WNV, owners should watch for fever, ataxia (lack of coordination), muscle twitching or weakness, head pressing (when a horse uses his head to push against an object to maintain balance), depression or apprehension, reduced appetite or vision, the inability to stand or swallow, unusual behavior, excessive tiredness, or convulsions. Affected horses can recover from WNV, especially those vaccinated against WNV.

Along with symptoms similar to WNV, EEE can make horses appear "dopey and lethargic," Johnson said.

"We do not have a specific treatment for these viruses, except to treat the symptoms as much as possible," Johnson said. "If horse owners are concerned about their animals, they should contact their veterinarian immediately. Recently, fewer people have been having their animals vaccinated due to the expense and low risk because of dry summers. However, the likelihood of disease will be higher this year because of all the water activity."

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