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What is EEE, Eastern equine encephalitis? Mosquito-borne disease death toll rises

Officials are urging some communities to cancel outdoor events after dusk, particularly activities that involve children.
/ Source: TODAY

Massachusetts on Friday reported the state's tenth human case of Eastern equine encephalitis, which health officials are calling "one of the most dangerous mosquito-borne diseases" in the U.S.

The patient, a man in his 70s from Bristol County, has died, making it the second EEE death in Massachusetts.

"It is absolutely essential that people take steps to avoid being bitten by a mosquito," said Monica Bharel, the state's public health commissioner, in a statement.

Earlier this week, Michigan reported four new human cases of EEE. Two of those patients died, bringing this season's EEE death toll in the state to three. One of the victims was Gregg McChesney, 64, who died last month, his brother told NBC affiliate WOOD TV.

"He was a perfectly healthy, happy human being and within a matter of nine days, he went from perfectly healthy to brain dead," Mark McChesney told the station.

With one fatality also reported in Rhode Island, the national death toll has risen to at least six.

"Michigan is currently experiencing its worst Eastern Equine Encephalitis outbreak in more than a decade," said Dr. Joneigh Khaldun, chief medical executive of the Michigan Department of Health and Human Services, in a statement Tuesday.

"The ongoing cases reported in humans and animals and the severity of this disease illustrate the importance of taking precautions against mosquito bites."

The health department is urging officials in the eight Michigan counties that have reported human or animal cases — Barry, Cass, Van Buren, Kalamazoo, Berrien, St. Joseph, Genesee and Lapeer — to postpone or cancel outdoor events after dusk, particularly activities that involve children, such as sports practices or games.

The recommendation is being made “out of an abundance of caution” and applies until the first hard frost of the year, the health department said. The Massachusetts Department of Public Health last week echoed that message, urging the public to stay indoors from dusk to dawn when mosquitoes are most active.

Only seven human cases of EEE are reported each year in the U.S. on average, according to the Centers for Disease Control and Prevention. Just six were reported in all of 2018.

But at least 22 human cases have already been confirmed so far this season in Massachusetts, Connecticut, Michigan, New Jersey and Rhode Island.

Why it's so deadly:

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 highest chance of infection in humans is typically August, though the peak time for transmission extends through September, officials have said.

Most infections happen in the Atlantic and Gulf Coast states, and some in the Great Lakes region, according to the CDC. Aerial mosquito spraying began last month in some of the communities at high risk for EEE.

“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.”

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.

What are EEE symptoms?

Symptoms start four to 10 days after a person is bitten and include:


high fever



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.

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.
  • Wear long-sleeved shirts and long pants when outdoors.
  • Get rid of anything in your yard that holds water, because mosquitoes need water to breed.

Climate change to blame?

As humans move closer to and deeper into hardwood forests, they’re increasing their risk, Conlon 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.”