Eastern Equine Encephalitis Virus Found in Northern Wisconsin

Eastern Equine Encephalitis Virus Found in Northern Wisconsin


Two cases of EEE have been diagnosed at WVDL this week. Both cases were from Northern Wisconsin in Crandon and Eagle River.  See below for the press release from DATCP.  Please contact the WVDL for any questions for testing or management of EEE in horses.



Equine encephalitis strikes in Northern Wisconsin 

Release Date: August 31, 2016

Media Contacts: Raechelle Belli, 608-224-5005

Bill Cosh, Communications Director, 608-224-5020


MADISON – A 2-month old unvaccinated filly from Forest County is the first reported Wisconsin horse to have become infected with Eastern Equine Encephalitis (EEE) this year. The filly was euthanized on August 23.


“Northern Wisconsin has good mosquito habitat. It’s also been a very wet summer up north, which contributes to the problem,” says Dr. Julie McGwin, equine program veterinarian for the Wisconsin Department of Agriculture, Trade and Consumer Protection.


EEE is caused by a virus transmitted by mosquitoes, and may cause encephalitis, or inflammation of the brain, and is fatal to horses in 90 percent of cases. Symptoms in horses include depression, appetite loss, drooping eyelids and lower lip, fever, weakness, twitching, paralysis or lack of coordination, aimless wandering, circling and blindness.


The virus is not contagious between horses, but can be carried by mosquitos from an avian, or bird, host to horses and humans. While humans may also be infected by EEE, the virus does not pass directly between people and horses. Mosquitoes biting warm-blooded animals is the only route of transmission.


Horses that have not already been vaccinated this year for EEE or other mosquito-borne diseases are at greater risk. “Those horse owners who have vaccinated should check with their veterinarians to see whether a booster is appropriate,” McGwin said.


Horses that have never been vaccinated will need two doses two to four weeks apart, and the vaccine will take at least two weeks to build up enough antibodies to protect them. Vaccines will not protect horses that have already been infected when they receive the injections. Vaccines are available that protect against other strains of equine encephalitis along with EEE, and a separate West Nile virus vaccine is also available.


Besides vaccination, McGwin recommends taking other steps to limit horses’ exposure to mosquitoes during warm weather:

  • Remove items from surrounding property that could collect stagnant water such as old tires, tin cans, plastic containers.
  • Keep rain gutters clean and draining properly.
  • Clean and chlorinate swimming pools, outdoor saunas and hot tubs, and drain water from pool covers.
  • Turn wading pools and wheelbarrows upside down when not in use.
  • Empty and replace water in birdbaths at least once a week.
  • Consider keeping horses in the barn from dusk to dawn, when mosquitoes are most active.
  • Discuss using equine mosquito repellents with your veterinarian.


Wisconsin last experienced a major outbreak of EEE in 2011, with more than 30 cases mostly in north central Wisconsin. Since then, sporadic cases have occurred. Because EEE follows mosquito populations, it normally occurs beginning in mid- to late summer and remains a threat until the first killing frost.