Eastern Equine Encephalitis (EEE; Triple E; sleeping sickness) has made its way back into the news again this year, with several documented equine and human cases in our area (Indiana and Michigan). It is important for horse owners to understand the clinical signs to look for and to be diligent about their vaccination programs.
Triple E, and several other less common viruses, are part of a group called alphaviruses, which is simply a description of what the virus looks like under a microscope and how it acts in real life. These viruses are passed to horses, humans, and other vertebrae species, and cause disease. It is important to note that these animals are considered “dead-end hosts”, meaning that they cannot pass it to other animals or humans. Mosquitoes also pass these viruses to birds, and it is thought that the birds can then serve as a source to infect more mosquitoes. Local disease surveillance often will test mosquitoes and dead birds for EEE and other diseases during the season to monitor the prevalence of the virus in the area.
Clinical signs of EEE center around the fact that the virus causes encephalitis (infection and inflammation of the brain tissues). Horses typically develop a fever, which may subside before neurologic signs are seen. Encephalitis usually results in horses that look like they have a headache – they may be dull or obtunded or appear unaware of their environment. As the brain swelling continues, they will become ataxic and wobbly, start head pressing or circling compulsively and ultimately may go down and be unable to get back up. The disease is usually fatal, with the course of disease lasting between 2-14 days.
As with most viruses, there is no specific treatment for the disease. Instead, management is focused on making the horse comfortable and decreasing the swelling of the brain while the virus is removed from the body. Supportive care includes IV fluid management, DMSO, dexamethasone, flunixin, Vitamin E, and sling support. However, as mentioned above, even with aggressive management, most horses will die.
The silver lining is that a highly effective vaccination is available for horses against this disease. This vaccine is recommended every 6-12 months, depending on your geographic location and risk of exposure. Talk to your veterinarian about their recommendations for your area. While a vaccine is not available for humans, it is important to minimize exposure to yourself and your family as well. Eliminating mosquito breeding grounds on your property by identifying low lying stagnant bodies of water is quite helpful. Additionally, using DEET bug spray during peak exposure times is important.
Each year, a few cases of EEE are identified in this area, and they are almost always fatal. Speak with your veterinarian to make sure your horse is up to date and safe!
Kristi Gran, DVM, DACVIM
Conley and Koontz Equine Hospital