Maine Reports Five EEE Horse Deaths, Three Suspect

Five horses in Maine have died of confirmed Eastern equine encephalitis (EEE) and animal health authorities are waiting on test results of another three "suspicious" cases, reported the Maine Department of Health and Human Services (Maine CDC) and the Maine Department of Agriculture's Animal Health and Industry Division.

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. Humans can also be infected via mosquitoes.

Last month, veterinarians identified EEE in three horses, 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.

"In all confirmed positive cases thus far, the horses were not up to date on their EEE vaccine or had a questionable vaccination history," said State Veterinarian Don Hoenig, DVM. "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."

In horses, EEE is a highly fatal disease with mortality approaching 100%. 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.

Horses are considered "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.

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.

"These five dead horses with EEE indicate that there is a risk of people contracting the infection from mosquito bites," said Dora Anne Mills, MD, MPH, 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."

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