A woman who contracted the mosquito-borne eastern equine encephalitis virus is the first person to die with the disease this year in Massachusetts.

Laurie Sylvia, who died Sunday at Tufts Medical Center in Boston, was the fourth person in the state to contract the disease this year, according to WBZ-TV.

"We are seeing the most intense level of EEE activity that we have in several years. The largest area is in Bristol and Plymouth counties with a second focus of activity in parts of Worcester and Middlesex counties," Public Health Commissioner Monica Bharel said in a statement Friday. "We are urging people across the state to remember that the peak time for transmission of mosquito-borne illness extends through September here in Massachusetts."

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On Monday, Michigan health officials said they're investigating three potential cases of the disease, Michigan Live reported.

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The eastern equine encephalitis virus is a rare cause of brain infections, or encephalitis, according to the Centers for Disease Control and Prevention. From 2009 through 2018, an average of seven cases were reported annually. Ten of those cases were in Massachusetts. Only Florida, with 13, had a higher number of cases.

Symptoms appear quickly after infection and include chills, fever, malaise and joint and muscle pain.

The virus kills about a third of infected patients, the CDC says. Those who recover may suffer with brain impairment, personality disorders, seizures and paralysis.