MISSISSIPPI STATE -- A recent case of Eastern equine encephalitis in Lamar County should remind owners of the importance of vaccinating horses against mosquito-borne diseases.

Eastern equine encephalitis is similar to West Nile virus in that it is spread primarily by mosquitoes that have fed on infected birds. EEE is spread by the Culiseta melanura mosquito and in horses is almost always fatal.

"While there is no treatment for the virus, horses vaccinated against Eastern equine encephalitis rarely come down with the disease," said Dr. Stanley Robertson, Mississippi State University Extension Service veterinarian. "Most outbreaks in horses occur when owners have not kept up with the vaccination schedule."

Adult horses need two initial shots three to four weeks apart, and foals should be vaccinated at 4, 5 and 6 months of age. All horses need an annual booster vaccination to protect them against EEE infection. The best time to vaccinate is in late spring, before the mosquito season begins.

EEE attacks a horse's central nervous system, primarily the spinal cord and brain.

"Symptoms happen fairly quickly after the horse has been bitten, usually between 24 and 72 hours," Robertson said.

"Infected horses may be unsteady on their feet, display erratic behavior, lose coordination, experience seizures, lose consciousness and die," Robertson added.

If an owner suspects a horse may have contracted the virus, it is important to immediately contact a veterinarian, who will diagnose the infection and take blood or tissue samples for confirmation. Some owners are reluctant to report suspect cases for fear of quarantine, but failing to report cases only postpones the mosquito control activities that could protect other horses.

Only mosquitoes can transmit the virus, so an infected horse poses no threat to humans or other horses.

As with West Nile virus, Robertson said in addition to vaccinating against the virus, horse owners should take steps to prevent mosquito activity around stable and pasture areas. The best way to keep mosquitoes at bay is to discourage breeding activity by eliminating standing water and cleaning water tanks or other sources of drinking water at least weekly.

"Improving the overall cleanliness of the premises can also limit vector activity, so frequent removal of manure and removing or trimming weeds can be beneficial," Robertson said. "In addition, keeping horses indoors during peak mosquito feeding times, such as at dusk and dawn, can cut down on the chances of getting Eastern equine encephalitis. Turning off barn lights or using fluorescent lights can minimize the attraction of adult mosquitoes into barns."

Keep air moving in stabling areas by using fans, and apply insect repellents that contain permethrins to horses especially during peak mosquito feeding times.

While extremely rare in people -- only 153 confirmed human cases of EEE have been reported in the United States since 1964 -- it is beneficial to avoid contact with mosquitoes. Extension entomologist James Jarratt advised taking precautions to avoid mosquito bites, especially during peak mosquito hours.

"If you're outside early in the morning or late in the afternoon, wear long pants and long-sleeved shirts," Jarratt said. "Apply an insect repellant that contains DEET to all exposed skin."

Follow label directions when applying DEET, and keep it out of the eyes. DEET is a repellant, not an insecticide, and keeps mosquitoes from landing and feeding on people.

"DEET is the most effective product on the market," Jarratt said.

He said some other products have some mosquito repellency, but none as much as DEET. Citronella candles are popular outdoor repellants, but Jarratt said breezes reduce their effectiveness by diffusing the substance in the air.

Although rare, the Association of State and Territorial Directors of Health Promotion and Public Health Education reports the effects of EEE can be devastating to an infected person. About half of patients infected die from the disease, and of those who survive, many suffer permanent brain damage and require lifetime institutional care.