Maine CDC Press Release

September 11, 2013

Horse in Oxford County Tests Positive for Eastern Equine Encephalitis (EEE)

AUGUSTA – The Maine Center for Disease Control and Prevention and the Maine Department of Agriculture, Conservation and Forestry announced today that a horse euthanized due to neurological signs last week in Oxford County tested positive for Eastern Equine Encephalitis (EEE). The horse was vaccinated for EEE and West Nile virus (WNV) a year ago, but had not received a booster dose.

EEE is a virus that is transmitted through the bite of an infected mosquito. Eight pools of mosquitoes have tested positive for EEE in York County this year. Maine last saw EEE in horses in 2009, when 15 horses died of the disease.

"EEE, which is carried by mosquitoes, is a fatal, viral disease in horses. The virus can affect human beings if they are bitten by mosquitoes that carry the virus," Dr. Michele Walsh, state veterinarian said. "People cannot acquire EEE infection from sick animals, only from the bite of an infected mosquito."

Steps Mainers can take to protect themselves from EEE and WNV include:

  • Wear long sleeves and long pants
  • Use an EPA approved repellent on skin and clothes
  • Take extra precautions at dusk and dawn
  • Use screens on your windows and doors
  • Drain artificial sources of standing water where you live, work, and play
  • Vaccinate horses against EEE and WNV

EEE virus is carried by mosquitoes, which pick it up from infected wild birds. The virus replicates in birds, which act as natural reservoirs for the disease.

Signs of the disease in horses include: stumbling or poor balance, unusual behavior and lethargy. Other symptoms include head pressing, circling, tremors, seizures and eventual coma. “EEE is preventable in horses through vaccination,” the state veterinarian advised. “If more than six months has elapsed since a horse has been vaccinated, a booster vaccination may be needed.” Vaccination can also protect against WNV, which has not been detected in Maine so far in 2013, but was detected in 2012, and has been detected in our neighboring states this year. Horse owners should contact their own veterinarians to decide if booster shots are needed. Revaccination is recommended if more than six months have passed since the last vaccination when exposure to infected mosquitoes is likely. Other animals besides people and horses can be affected by EEE. The virus can also affect specialty livestock, such as llamas, alpacas, emus, ostriches and other farm-raised birds, such as quail and ducks.

"This EEE activity in mosquitoes and horses should serve as a reminder to health care providers that humans are at risk from this disease, as well," says Dr. Sheila Pinette, Director of Maine CDC. Although many persons infected with EEE have no apparent illness, those who develop symptoms do so usually three to 10 days after the bite of an infected mosquito.

Symptoms range from mild flu-like illness to encephalitis, coma and death. Approximately half of people who have symptoms of EEE will have mild to severe permanent neurological damage and EEE is fatal in about one of every three cases.

Maine's Health and Environmental Testing Laboratory performs arboviral testing for mosquitoes, large animals and humans. Submission information can be found at

For more information: Maine CDC's arboviral website:

Maine's weekly arboviral surveillance reports:

HETL's submission form and information: Department of Agriculture, Conservation and Forestry website: