ST. PAUL — Three horses in Minnesota were euthanized recently after testing positive for or exhibiting symptoms of different equine diseases, state officials said Thursday, Sept. 9.

One of the diseases, which is said to be rare, can infect humans though not through contact with a horse. Called Eastern equine encephalitis, or EEE, it is spread to humans and horses by mosquitoes carrying the disease, according to the Minnesota Board of Animal Health.

In a phone interview, board spokesperson Michael Crusan referred to the discovery of EEE in Itasca County as a "canary in the coal mine moment." The board in a news release said it indicates the presence of other infected mosquitoes in the area and encouraged horse owners to vaccinate their horses against the disease, which almost always proves fatal.

The horse infected with EEE was a 6-year-old quarter mare, according to Thursday's release. It was euthanized on Aug. 16 after exhibiting signs of neurologic disease such a loss of muscle control, inability to stand and eventually convulsions, and testing confirmed that it had the disease.

The horse never left the farm it was born on, according to the release, and "had no history of vaccination" against EEE. Nine other horses on the farm have been vaccinated for rabies and are scheduled for EEE and other vaccinations, the release said.

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Two horses in Washington County, meanwhile, were euthanized in recent weeks following the discovery there of Equine Herpesvirus Myeloencephalopathy, or EHV-1. One was put down on Aug. 27 after showing signs of progressive loss of muscle control, the news release said.

A second horse on the Washington County farm was euthanized a week later after showing similar symptoms but was not tested, the release said. The highly contagious disease spreads primarily through horse-to-horse contact, according to the board, and can remain inactive for extended periods of time.

According to the release, the EHV-1 horses were present for shows held at the Washington County Fairgrounds Aug. 14, in Lindstrom Aug. 20 and in Hugo Aug. 21. The board reached out to those locations to "alert clients or attendees as an extra precaution."

Asked about the possible spread of EHV-1 to other horses, Crusan said Thursday there was "no direct exposure that we are aware of."