A horse in York County tested positive for Eastern equine encephalitis and had to be euthanized, the Maine Center for Disease Control and Prevention reported Friday.

State health officials issued a warning this week about the rare mosquito-borne disease, which can be fatal. No human cases have been reported in Maine since 2015, but other Northeast states have experienced recent cases, including one death in Massachusetts.

Maine CDC officials said the horse was not vaccinated against the disease. This was the first known instance of a horse in Maine contracting EEE since 2013.

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

Still, officials repeated the warning for residents to take precautions against mosquito bites.

“This positive result confirms that mosquitoes carrying the virus are present in Maine, which is the reason why Maine CDC urges the state’s residents and visitors to take precautions to protect themselves and their animals from mosquito bites,” Maine CDC Director Dr. Nirav D. Shah said in the statement. “We want everyone to take precautions while enjoying themselves this holiday weekend.”

Many states, although not Maine, also have seen positive results in humans and mosquitoes for West Nile virus, which causes symptoms similar to EEE.

State officials also informed animal owners that a vaccine for EEE and West Nile virus is available for horses, and they encouraged those that have not been vaccinated in the last six months to get the initial shot or a booster. Officials also warned that the virus can affect specialty livestock, like llamas, alpacas, emus, ostriches and other farm-raised birds, such as pheasants, quail and ducks. They advised owners to contact their veterinarians to discuss available vaccines and other precautions.

EEE was first detected in birds in Maine in 2001. In horses, the symptoms include stumbling or poor balance, unusual behavior and lethargy. Other signs are head pressing, circling, tremors, seizures and coma. Some species experience bloody diarrhea or sudden death. In animals, the fatality rate is 90 percent, and the survivors can have permanent brain damage.

In humans, those who develop symptoms may experience mild flu-like illness to high fever, headache, stiff neck and decreased consciousness. About one in every three individuals who are infected with EEE dies and many of those who recover experience lasting health problems. Individuals with symptoms suggesting an EEE infection should contact their physician immediately, although there is no vaccine for humans and no specific antiviral treatment for either EEE or West Nile virus.

CDC officials said people should minimize outdoor activity from dusk to dawn, when mosquitoes are most active. When outdoors, people should use an EPA-approved insect repellent, wear long-sleeved shirts and pants, treat clothing with Permethrin and manage mosquitoes around their property.

More information on preventing EEE and WNV is available on the CDC website at: https://www.cdc.gov/EEE/ or www.cdc.gov/westnile.