A Massachusetts woman has died after contracting Eastern equine encephalitis, or EEE, which health officials are calling "one of the most dangerous mosquito-borne diseases" in the U.S.

Laurie Sylvia passed away while receiving treatment for EEE at Tufts Medical Center in Boston, a hospital spokesman confirmed to TODAY. There have now been four human cases of the rare disease in Massachusetts this season, the state's Department of Public Health announced Sunday.

Michigan has confirmed one human case of EEE and is investigating three other possible cases, the state's Department of Health and Human Services said Monday.

Tufts declined to release any other details about Sylvia's case, citing patient privacy laws, but her family said she died over the weekend.

Sylvia, 59, of Fairhaven, Massachusetts, was a realtor who often traveled so it's not clear where she was bitten by a mosquito carrying the virus, her husband Robert Sylvia, Jr. told NBC 10 Boston. She started feeling sick last Monday, he added.

"I just don't understand how such a beautiful person could be taken from me so soon," her daughter Jen Sylvia wrote in a Facebook post. "She brought light and joy to everyone she came across."

Earlier this month, the daughter of a Massachusetts man diagnosed with EEE revealed he was in a coma. The family's life has been "flipped upside down" since the diagnosis, she wrote on Facebook. His loved ones didn't know where or when he was bitten by a mosquito.

'Take this risk very seriously'

Parts of Massachusetts have been at “critical risk” for EEE since mid-August when lab tests confirmed the first human case of the disease in the state since 2013.

The virus — which is more virulent than West Nile — can cause inflammation of the brain that leads to death in about one-third of cases. People who do survive are often left with brain damage.

The virus has been found in 333 mosquito samples this year, the Massachusetts Department of Public Health noted.

“We are asking residents to take this risk very seriously,” said Dr. Monica Bharel, the state’s public health commissioner, in a statement.

The highest chance of infection in humans is typically August, though the peak time for transmission extends through September, officials said. So far this year, 37 communities in Massachusetts have been found to be at high or critical risk for EEE. Aerial sprays have been targeting Worcester and Middlesex counties to reduce the mosquito population.

The virus has also been found in three horses in Massachusetts, six horses and two deer in Michigan and four chickens in Delaware this month. Mosquito samples also show the virus was present in New Hampshire.

“It’s concerning from a public health point of view, no question about it,” Joe Conlon, a retired U.S. Navy entomologist and spokesman for the American Mosquito Control Association, told TODAY.

“(But) it’s not a very wide-spread disease, thank goodness… it’s not common like West Nile virus.”

Only a few cases of EEE are reported in the U.S. each year, with most infections happening in the Atlantic and Gulf Coast states, and some in the Great Lakes region, according to the Centers for Disease Control and Prevention. Just six cases were reported in all of 2018.

The virus grows in birds that live in swamps. When a mosquito that feeds on both birds and mammals bites an infected bird, it can then transmit the virus to horses and other animals and, in rare cases, people.

Anyone in an area where the virus is circulating can get infected, though people who work or exercise outdoors, or live in wooded areas face the highest risk.

Symptoms start four to 10 days after a person is bitten and include headache, high fever, chills and vomiting. As the disease progresses, the patient can suffer from disorientation, seizures and coma. There is no specific treatment.

“They give you palliative care and you either get better or you die,” Conlon said.

As humans move closer to and deeper into hardwood forests, they’re increasing their risk, he noted. Climate change plus human travel and migration may also play a role in mosquito-borne diseases, potentially exposing half of world’s population to disease-spreading mosquitoes by 2050, an analysis published in Nature Microbiology in March found.

But other studies have found the ban on the insecticide DDT, rather than a warming climate, may be responsible for mosquitoes thriving in the U.S. It appears many factors are at play.

“If the climate change that’s occurring is producing higher temperatures and more rainfall, that’s going to abet this type of disease transmission,” Conlon noted.

“In addition, the world is getting smaller. Tourism and travel is getting a lot cheaper, a lot more widespread. We’re putting travelers in contact with these exotic diseases that are a seven-hour plane flight away. They’re bringing these diseases in some cases back to the U.S.”

His main concern now is keeping mosquito-borne disease like Rift Valley fever, found in Africa, and yellow fever, found in South America and Africa, out of the U.S.

How to reduce the chance of getting infected with EEE:

  • There is no vaccine, so preventing mosquito bites is key
  • Stay indoors at dawn and dusk, when the mosquitoes that transmit the virus are active, Conlon said
  • Use a mosquito repellent with an EPA-registered ingredient
  • Mosquitoes need water to breed, so get rid of anything in your yard that holds water