COLUMBIA, Mo. – 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 equine veterinarians Philip Johnson and Alison LaCarrubba say Missouri horse owners 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, a professor of veterinary medicine and surgery. “However, horse owners need to be extremely cautious this year because the warm, wet weather and extensive flooding increases the risk of WNV spreading.”
WNV 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 U.S. Department of Agriculture Animal and Plant Health Inspection Service (APHIS). However, this is commonly underreported, Johnson said.

Owners should vaccinate their horses against WNV and EEE, giving vaccination boosters annually. They should also drain water from flooded pastures or paddocks, water troughs, ornamental water decorations, gutters, and other sources of standing water. They also can utilize nontoxic water treatment products that kill mosquito larvae, which are commercially available.

Though most infected horses do not exhibit clinical signs of WNV, owners should watch for fever, ataxia or 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 West Nile Virus, 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.”
Equine veterinarians in the MU Veterinary Medicine Teaching Hospital are available to help veterinarians identify WNV and provide consultation for the treatment of affected animals. To contact the MU Veterinary Hospital during normal business hours, Monday-Friday 8 a.m.-5 p.m., call (573) 882-3513. For emergencies after hours and on weekends, call (573) 882-4589. To contact the MU Veterinary Medical Diagnostic Lab, call (573) 882-6811.

Owners should immediately report a suspected or confirmed case of WNV to the Missouri state veterinarian at (573)751-3377 and/or to USDA-APHIS Veterinary Services at (573) 636-3116.