Eastern Equine Encephalitis Found in Horse Populations

Posted: November 12, 2007

Ohio Department of Agriculture (ODA) officials confirmed the discovery of eastern equine encephalitis (EEE) virus - a mosquito-borne viral disease - in a central-Ohio horse and a northwest-Ohio horse.

INDIANAPOLIS (23 October 2007)-The number of counties with horses testing positive for Eastern equine encephalitis (EEE) has mushroomed to 17-the widest dispersion of the virus in recent memory, according to veterinarian Sandra Norman, Equine Director for the Indiana State Board of Animal Health. Laboratories have reported 24 test-positive horses this year.

            "Typically, in years when we receive reports of EEE, we see them clustered in the most northern counties in Indiana, particularly on the western side of the state," Dr. Norman said. "Michigan reports cases nearly every year."

            Counties with EEE-positive horses this year include: Dekalb, Elkhart, LaPorte, St. Joseph, Adams, Putnam, Boone, Howard, Daviess, Steuben, Noble, Rush, Jay, LaGrange, Decatur, Hendricks and Kosciusko.

            Because the virus is carried by mosquitoes, new EEE-positives will likely surface up to-and even slightly beyond-freezing temperatures that will kill the flying pest populations.

            For currently unvaccinated horses, a vaccine given now may be too late to offer protection this season; an animal's immune system will build gradually after two doses, administered three weeks to six weeks apart.

"But vaccinating now is certainly better than not at all-plus it gives the horses a jump-start for protection next year," added Dr. Norman. "EEE should be part of a horse's annual health regimen."

            Meanwhile, horse owners should take steps to protect their animals by eliminating potential breeding sites-even very small pools of water can harbor more mosquitoes. Horses should also be kept sheltered during high-activity flight times near dusk.

             EEE is a mosquito-borne arbovirus that causes central nervous system problems in horses that cannot be cured. Horses are dead-end hosts for the disease and cannot spread the virus directly to humans (who are also susceptible); mosquitoes must feed from infected birds to spread the virus. Infected horses may exhibit a variety of central nervous system signs, such as seizures, as well as a fever. Owners should consult a veterinarian as quickly as possible to seek supportive care for their animals.

Kentucky Dept of Agriculture quarantines horses for equine herpes virus:



FRANKFORT, Ky. — The Kentucky Department of Agriculture has imposed a quarantine in a barn at Churchill Downs in Louisville where a horse tested positive for equine herpes virus.

 “These measures were taken to protect other horses on the grounds as Churchill Downs prepares to open its fall meet,” said State Veterinarian Dr. Robert C. Stout. “At this time there are no restrictions on movement of other horses at Churchill.”


A 3-year-old Thoroughbred trained by David Carroll presented symptoms Thursday. The horse, a resident horse at the track, was transported to an equine hospital in Lexington. Carroll has 19 horses in the barn, including a stable pony, and another 16 horses in Barn 47 are under the care of trainer Al Stall.

The KDA also has ordered biosecurity measures at the track to guard against the introduction of the virus to the rest of the horse population. Horses that ship in to race will be allowed only in the track’s receiving barn.  Rusty Ford, the equine programs manager in the state veterinarian’s office, said test results suggested the affected horse has a low level of the virus, which implies the amount of virus capable of transmission is reduced, thus lowering the transmissibility of the virus to other horses in the barn.

 Equine herpes virus occurs primarily in younger horses. It can be transmitted by direct or indirect contact with an infected horse or contaminated material. It also may be spread through the air when a horse coughs. Symptoms most commonly include fever and an upper respiratory infection. Symptoms also may include lethargy, loss of appetite, a nasal discharge and a cough. In severe cases, horses can lose coordination and become unable to stand. The virus can be fatal.


Historically a quarantine for equine herpes virus remains in effect for 21 days from the time of potential exposure to the virus. Officials will observe the horses for signs of disease. Samples have been taken from each horse in the barn to test for the presence of equine herpes virus. Test results will be available next week. The horses will be tested again before the quarantine is lifted.


From the Ohio Dept. of Agriculture

REYNOLDSBURG, Ohio (Oct. 17, 2007) – Ohio Department of Agriculture (ODA) officials today confirmed the discovery of eastern equine encephalitis (EEE) virus — a mosquito-borne viral disease — in a central-Ohio horse and a northwest-Ohio horse. These cases, found in Orient and Harrod, mark the first in Ohio since 2005, when a case was reported in Trumbull County.


The virus, which is spread through infected mosquitoes, can be fatal to horses if they are not properly vaccinated. Dr. Tony Forshey, ODA state veterinarian, urges equine owners to vaccinate their animals.


“Horses are highly susceptible to EEE, and vaccination can be an effective tool in combating this deadly virus. Horse owners should take all necessary precautions, including the implementation of good mosquito control.”


The ODA Animal Disease Diagnostic Laboratory in Reynoldsburg confirmed EEE in both Ohio horses. The virus, which has been found in several surrounding states, is most commonly spread in and around freshwater hardwood swamps in the Atlantic and Gulf Coast states as well as in the Great Lakes region. The virus can be fatal to horses, causing death within two to three days of onset.


According to the Centers for Disease Control and Prevention (CDC), human cases occur relatively infrequently, largely because the primary transmission cycle takes place in and around swampy areas where human populations tend to be limited. However, humans should avoid mosquito bites by employing personal and household protection measures, such as using an EPA-registered repellant according to manufacturers' instructions, wearing protective clothing, avoiding outdoor activities when mosquitoes are active, and removing standing water that can provide mosquito breeding sites.


For more information regarding the EEE virus, visit the CDC Web Site at

 DISCLAIMER: This notification does not constitute a press release from the Pennsylvania Department of Agriculture. The content is intended for the informational purposes of those involved in the animal health community in the Commonwealth.