A horse in Douglas, Massachusetts, has tested positive for eastern equine encephalitis, prompting the state to raise the risk level for infection to critical, health officials said Tuesday.
The risk level in neighboring Oxford and Webster has also been raised to high.
There are now 29 Massachusetts communities at critical risk, 39 at high risk and 123 at moderate risk for the EEE virus.
Eight horses in Massachusetts have now tested positive for EEE this year, according to the state health department. A goat has also tested positive.
"Cases of EEE in mammals, including horses, serve as a reminder that there is a continuing risk to humans," Public Health Commissioner Monica Bharel said. "Even as we head into September, it remains critically important that people take steps to protect themselves and their families from mosquito bites."
EEE is a mosquito-borne virus that can affect the nervous system and kills about 1 in 3 people who contract it, according to the U.S. Centers for Disease Control and Prevention.
Already this year, EEE has been found in 379 mosquito samples. The state recently completed spraying from airplanes in parts of Bristol, Plymouth, Middlesex and Worcester counties to help mitigate the mosquito population, but that spraying has concluded for the season.
To protect against EEE, use bug spray, wear long sleeves and pants outdoors and avoid activities in the evening and early morning, when mosquitoes are most active, health officials say.
Before this year, the last EEE outbreak in Massachusetts was between 2010 and 2012.