By JANE HOUIN
Ohio Correspondent

REYNOLDSBURG, Ohio — In mid-September, the Ohio Department of Agriculture (ODA) confirmed cases of Eastern Equine Encephalitis (EEE) in two horses that died on a farm in Mercer County.
This was the first incident of EEE in Ohio in 10 years. At this time, there are no known human illnesses associated with this confirmation.

Eastern Equine Encephalitis is one of several contagious types of ecephalomyeltis that cause sickness and death in horses by affecting the central nervous system. It is caused by a virus that can infect birds, horses and humans. It is transmitted by mosquitoes, and outbreaks typically occur in late summer and early fall when mosquitoes are most abundant.

According the American Assoc. of Equine Practitioners (AAEP), clinical signs of infection include behavioral changes, loss of appetite and fever.

These can progress in 12-24 hours to dementia with head pressing, teeth grinding, circling and often blindness. The disease is fatal in up to 90 percent of cases, making it the most deadly of the three types of encephalidites found in the United States. There is no treatment for EEE aside from supportive care. And typically, infected horses with clinical symptoms die within 3-5 days after onset of clinical signs. Those who do survive are left with residual mental dullness.

However, an effective equine vaccine does exist for EEE, making prevention especially important since there is no treatment or cure for the disease in horses. According to the AAEP, young horses are particularly prone to the disease. Adult horses with an unknown vaccination history or who have never been vaccinated against EEE should receive a primary series of two vaccine doses with a four to six week interval between doses with revaccination prior to the onset of the next vector season or annually thereafter.

For adult horses who have been previously vaccinated, AAEP recommends an annual revaccination prior to the vector season in the spring. High-risk animals or those with limited immunity may require more frequent vaccinations. In areas where mosquitos are active year round, many veterinarians elect to vaccinate at 6-month intervals to ensure uniform protection throughout the year although this practice is not specifically recommended by vaccine manufacturers.

Pregnant mares who have previously received the vaccine should be revaccinated four to six weeks before foaling. Those mares with unknown vaccination history or who have not been vaccinated should immediately begin a two-dose primary series with a four week interval between doses and a booster 4-6 weeks before foaling or prior to the onset of the next vector season - whichever comes first.

Foals from mares vaccinated in the pre-partum period should begin a three-dose series at 4-6 months of age with 4-6 weeks between the first and second dose.

The third dose should be given at 10-12 months of age and prior to the onset of the next mosquito season.

Foals from unvaccinated mares or those with an unknown vaccination history should begin their three-dose series at three to four months of age with a four-week interval between the first and second doses. Third dose procedures are the same as for foals from vaccinated mares.

Horse-to-horse transmission and horse-to-human transmission by mosquitoes is very unlikely because of the small concentration of the virus in horses affected by EEE. Transmission typically occurs via mosquitoes from birds or rodents, which are natural reservoirs for the virus.

EEE infection is rare in humans, but when it does occur, it can be serious. The Ohio Department of Health (ODH) urges Ohioans to take steps to avoid mosquito bites, such as wearing light-colored long pants and long-sleeved shirts as well as socks and shoes.
In addition, to avoid mosquito bites for both animals and humans, the ODA and ODH recommend insect repellants be used according to label directions.

Mosquitoes can be active until the first frost and will stay infected, and capable of transmitting viruses, as long as they live. EEE outbreaks have been historically restricted to the eastern, southeastern and some southern states according to AAEP.
Suspect equine cases should be reported to local veterinarians and the ODA, and any suspect human cases should be reported to the local health department.