Maine CDC Press Release

September 2, 2009

Number of Horse Deaths to EEE Increases to Five

Maine CDC and the Maine Department of Agriculture’s Animal Health and Industry Division announced today that a total of five horses in Maine have died of confirmed Eastern Equine Encephalitis (EEE) and three more are suspicious, awaiting test results.

Two More Equine Deaths Confirmed; Three Other Deaths Suspicious

Augusta - The Maine Center for Disease Control and Prevention in the Maine Department of Health and Human Services (Maine CDC) and the Maine Department of Agriculture's Animal Health and Industry Division announced today that a total of five horses in Maine have died of confirmed Eastern Equine Encephalitis (EEE) and three more are suspicious, awaiting test results.

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 mammals in 2005 among two horses in York County, and was also found that year in some mosquitoes and birds in York and Cumberland Counties. In the fall of 2008, a man spending time in Cumberland County and a horse from York County died of the infection.

Last month. three horses were identified with EEE, two in Waldo County and one in Penobscot County. This week, a horse in Cumberland County (Gorham) and another in Waldo County (Unity) have been confirmed to have died of EEE. Two more horses from the Waldo County town of Unity and one from the York County town of Berwick are suspicious, pending test results.

"These five dead horses with EEE indicate that there is a risk of people contracting the infection from mosquito bites," said Dr. Dora Anne Mills, Director of the Maine CDC. "Although the risk of contracting the infection from one mosquito bite is very low, it now appears the risk is geographically fairly widespread, given that it has now been detected in these various locations this year. We can assume other areas of the state have infected mosquitoes as well. Until we experience several deep frosts, it is important people take precautions to avoid getting bitten by mosquitoes."

"In all confirmed positive cases thus far, the horses were not up to date on their EEE vaccine or had a questionable vaccination history," reminded Dr. Don Hoenig, DVM, State Veterinarian. "It is important for horse owners to know there is a very effective annual vaccine for EEE and they should be sure their horses are current on this vaccine".

Steps people should take 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 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 their horses annually.

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. About one-third of those who have symptoms of EEE die. Approximately half of those identified with EEE and who survive will have permanent neurological damage. Unlike horses, there is no vaccine available for humans. There is also no known effective treatment.

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, especially near wetlands
  • 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

"It is especially important with schools starting that those schools near wetlands or taking field trips to wetlands assure parents and children are aware of the importance of protecting themselves," cautioned Dr. Mills.

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. Dr. Hoenig also reports that horses are considered to be “dead end” hosts for the disease meaning that they are not capable of transmitting the disease to humans or other horses. Infection must occur through the bite of an infected mosquito.

Maine CDC is working with partners to trap and test mosquitoes in Waldo County as well as other areas of the state to help determine the geographical scope of the risk. Although EEE has been detected along the Eastern United States for a number of years, these recent cases in Maine are the farthest north the disease has been identified. Area Maine CDC staff are also working with municipalities and some local schools to inform them of the risks and of their options for controlling the mosquito population.

US CDC "Fight the Bite" Mosquito Website Maine CDC EEE Website US CDC EEE Website Maine Department of Agriculture Animal Health Website

Resources to learn more about mosquito control include:

  • University of Maine Cooperative Extension at 1-800-287-0279,
  • Maine Forest Service at 207-287-2431 or,
  • Board of Pesticide Control at 207-287-2731 or (information on pesticide regulations, licensed applicators, pesticide effects)
  • Maine Department of Environmental Protection (Maine DEP) information on pesticides and wetlands at 207-287-3901 or 1-800-452-1942