Sussex horse tests positive for Eastern Equine Encephalitis

Third horse this year
September 20, 2013

A horse from Sussex County has tested positive for Eastern Equine Encephalitis, a mosquito-borne disease, the Delaware Department of Agriculture announced Sept. 19.

The yearling filly was showing signs of severe neurologic disease and was under the care of a veterinarian. Despite receiving supportive care, the horse showed no improvement, and was humanely euthanized.

This is the third Delaware horse this year to be diagnosed with a mosquito-borne disease. Two horses have previously been diagnosed with West Nile Virus, and both have recovered. The last case of equine EEE in Delaware was in 2005. There is no treatment for either West Nile Virus or Eastern Equine Encephalitis.

"With the large mosquito population this year, we continue to urge equine owners to have their horses vaccinated and consult with their veterinarians about maintaining a vaccine program," said State Veterinarian Dr. Heather Hirst, who heads the Department of Agriculture's Poultry and Animal Health Section. "Vaccination can increase a horse's protection against these sometimes fatal diseases. Prevention is still cheaper than care - and far better than having a horse suffer or die.”

Unvaccinated horses are at greatest risk of developing clinical signs from both Eastern Equine Encephalitis and West Nile Virus, which are spread by mosquitoes and can be fatal. Both horses and humans can contract WNV and EEE if bitten by a mosquito carrying the virus, but it is important to note that the viruses are not transmitted between horses or from horses to people. The viruses normally exist in a cycle between mosquitoes and birds, but occasionally EEE can be transmitted from mosquitoes to mammals.

Hirst said horse owners should contact their veterinarian immediately if they suspect their horse may be showing signs of WNV or EEE. Symptoms of EEE in horses include fever (102.5-104.5°F), loss of appetite, head pressing, depression or personality change, wobbling or staggering, weakness, blindness, convulsions, muscle tremors in the head and neck, and hind-limb weakness. These signs are also consistent with WNV, although a fever may or may not be present with WNV.

Prior to 2013, Delaware’s last confirmed equine case of WNV was in 2003, and the last case of equine EEE was in 2005.

To reduce mosquito breeding, the Department of Natural Resources and Environmental Control advises people to drain or remove items that collect water, such as discarded buckets or containers, uncovered trash cans, stagnant birdbaths, unprotected rain barrels or cisterns, old tires, upright wheelbarrows, flowerpot liners, depressions in tarps covering boats, clogged rain gutters, downspout extenders, and unused swimming pools.

For more information about:

• Mosquito biology/ecology and control:  Contact the Mosquito Control Section’s Dover office at 302-739-9917.

• WNV in humans and related medical issues: Contact the Delaware Division of Public Health at 888-295-5156.

• WNV or EEE in horses and equine vaccines: Contact the Department of Agriculture’s Poultry and Animal Health Section at 302-698-4500 or 800-282-8685 (Delaware only).

• West Nile virus: go to the CDC website,



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