Massachusetts is in the midst of an outbreak of eastern equine encephalitis, or EEE, and large swaths of the state are at risk, according to the health department.
Several towns in Bristol, Plymouth and Worcester counties are at critical risk of the rare virus that can kill people who get it, along with a few towns elsewhere.
The state says that four people have been diagnosed with EEE this year, along with seven horses.
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It's the first outbreak of EEE in the state since 2012.