Maine CDC Press Release

August 11, 2009

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

Dora Anne Mills, MD, MPH
Phone: (207) 287-3270
John Martins, Director
Employee and Public Communications
Phone: (207) 287-5012

AUGUSTA - The Maine Center for Disease Control and Prevention in the Maine Department of Health and Human Services and the Maine Department of Agriculture’s Animal Health and Industry Division announced today that a four-year-old quarter horse gelding euthanized last week in the town of Troy in Waldo County, has tested positive for Eastern Equine Encephalitis (EEE).

EEE is a virus that is transmitted through the bite of an infected mosquito that has picked up the virus by feeding on an infected bird. The disease was first detected in Maine in 2005 among some horses, mosquitoes, and birds in York County.

“A horse with EEE does not pose a health threat to humans. However, a horse with EEE indicates that local mosquitoes are infected, contracting it from birds,” said Dr. Dora Anne Mills, Director of the Maine CDC. “Since mosquito bites are how EEE is transmitted to humans and horses, it is important people and horse owners take precautions.

“We had regarded southwest Maine as the perceived area of greatest risk for EEE,” said Dr. Don Hoenig, State Veterinarian with the Department of Agriculture. “However, this case in Waldo County indicates that the area may be much wider.”

Steps people should consider to protect themselves from EEE include:

  • Using an effective insect repellent on skin and clothing such as DEET or another EPA-registered repellent;

  • Covering up with long-sleeve shirts, pants and socks when outdoors;

  • Placing mosquito netting over infant carriers when you are outdoors with infants;

  • Being aware that mosquitoes are most active at dawn and dusk;

  • Cleaning up unnecessary standing water around the yard to reduce mosquito habitats; and

  • Vaccinating horses.

“Several of these steps also help protect against tick bites, which are the transmitter of Lyme Disease that was reported in about 900 Mainers in 2008,” Dr. Mills said.

Although many persons infected with EEE have no apparent illness, those who develop symptoms do so usually 3 to 10 days after the bite of an infected mosquito. Symptoms range from mild flu-like illness to encephalitis, coma, and death. The case fatality rate is about one-third. Approximately half of people who have symptoms of EEE will have mild to severe permanent neurological damage.

The transmission cycle of EEE among birds and mosquitoes is most common in coastal areas and freshwater swamps. Human cases occur relatively infrequently, largely because the primary transmission cycle takes place in swamp areas where human populations tend to be limited. Those people at most risk are:

  • Residents of and visitors to endemic areas

  • People who engage in outdoor work and recreational activities

  • Persons over age 50 and younger than age 15 seem to be at greatest risk for developing severe disease

In horses, EEE is a highly fatal disease with mortality approaching 100 percent. Infected horses can exhibit clinical signs of illness within 3-10 days of being bitten by an infected mosquito. Clinical signs include unsteadiness, erratic behavior and a marked loss of coordination. There is no effective treatment and seizures resulting in death usually occur within 48-72 hours of an animal's first indications of illness.

“All horse owners should be sure their horses are current on their EEE vaccination, as this is a very effective vaccine,” reminded Dr. Don Hoenig. “The horse that was positive in Troy was not vaccinated.”


US CDC “Fight the Bite” Mosquito Website

Maine CDC EEE Website

US CDC EEE Website

Maine Department of Agriculture Animal Health Website