A man from Michigan died last month after contracting the rare Eastern equine encephalitis (EEE) virus from a mosquito earlier in the summer, and now health experts are saying the case could highlight an emerging medical threat in the northeastern United States. 

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Michigan man dies after mosquito bite

According to his family, Gregg McChesney, 64, was bitten by a mosquito while helping install docks on a pond. A few days later, he suddenly had a seizure. Gregg's brother, Mark, said, "[N]ext thing you know, he's in the [ED] and he just never came out of it."

According to Mark, it was as if Gregg went from being "perfectly healthy to brain dead" within nine days of contracting the virus.

Days after Gregg passed, doctors confirmed that he'd contracted EEE.

Gregg is one of at least seven people from Michigan who were infected with EEE in July, according to the state Department of Health and Human Services.

What is EEE?

EEE is an arbovirus, or a virus that is spread by a mosquito or other arthropod. The virus has mostly been found in the northeast United States, as well as in the Gulf Coast and Great Lakes.

The virus is extremely rare—the United States sees an average of seven cases per year, according to CDC—but for some it can be deadly.

Marc Fischer, a medical epidemiologist with the CDC's arboviral disease branch, located at Fort Collins, Colorado, said some people some people only experience mild flu symptoms, but about 20% of people develop a clinical illness and about half of those patients develop neuroinvasive disease—a deadly disease that causes the brain to inflame. About one-third of patients with EEE who develop encephalitis die, and survivors of the illness usually have lasting side effects, like brain damage, according to STAT News.

"It is the highest case fatality of all of the arboviruses that occur in the United States," Fischer said.

Most patients who develop EEE will experience sudden and severe symptoms four to 10 days after a mosquito bite. The symptoms will usually begin with a sudden headache, followed by a high fever, chills, and vomiting, and eventually disorientation and seizures, according to STAT News. People older than 50 and people younger than 15 are at highest risk of becoming seriously ill from the virus.

CDC reports higher than usual EEE cases

While Fischer noted the number of EEE cases each year are small, particulatly when compared with West Nile virus, officials have noticed an uptick in EEE cases reported this year. So far, six states have reported 20 cases of EEE, with Massachusetts and Michigan reporting nine and seven cases, respectively. Six of the infected patients have died.

Scott Weaver, an arbovirus expert at the University of Texas Medical Branch in Galveston, said, "What's a little bit concerning is that we're already at the upper limit of the normal range and it's still only mid-September." He added, "In Massachusetts and other areas of the northeast and mid-Atlantic, we may have another month or even more of active transmission and more cases to come."

While researchers are working on and testing vaccinations for EEE, there is no vaccine available to the general public in the United States. According to STAT News, "because cases are so uncommon," in humans "there isn't a … market for EEE vaccine." And "without a market there's no chance one will get made" (Branswell, STAT News, 9/23; Iati, Washington Post, 9/19).