Thirty-seven other communities are at high risk and another 126 are at moderate risk, health officials said.
Four people have confirmed cases of the virus this year. In addition, it was detected in seven horses and found in 366 mosquito samples, said the state health authorities.
"On the way to the Labor Day weekend and the month of September, people should not forget to bring an EPA-approved mosquito repellent for all outdoor activities," Dr. Monica Bharel, the state health commissioner, in a press release. "The peak time for the transmission of mosquito-borne diseases will reach here in Massachusetts by September."
Holliston, Medfield, Brookfield and Granby are among the most vulnerable communities.
The virus is sporadic in the state. There were recent outbreaks in 2004-2006 and 201
The state has sprayed from the air to kill mosquitoes, but health officials say the risk has not been eliminated.
Residents are encouraged to protect themselves with mosquito repellents from the virus.