(CNN) - A man in Massachusetts has been infected with a mosquito-borne virus called Eastern equine encephalitis (EEE), health officials confirmed Saturday. It's the first human case reported in the state since 2013.
At least nine towns are at "critical risk" of exposure to the rare but potentially fatal virus, which can cause brain swelling, according to the Massachusetts Department of Public Health.
It's the latest in a series of warnings from state officials about the virus, which has been detected in 227 samples of mosquitoes in 2019, the health department said.
Florida and Delaware issued similar advisories this summer after the virus was detected in sentinel chickens, though neither state has seen any cases reported in humans.
Any virus transmitted from an insect bite is a big deal, but what is EEE, and what risk does it pose?
EEE is rare but often fatal
The virus isn't common, but it is serious. Seven cases are reported every year on average, but about 30% of all cases are fatal, according to the Centers for Disease Control and Prevention.
EEE causes inflammation of the brain, which is often preceded by a high fever, chills and vomiting. As the illness progresses, patients might experience seizures or a coma that can cause varying degrees of brain damage, the CDC said.
Infections are commonly reported in the summer (mosquitoes thrive in heat and humidity) in states that border the Atlantic Ocean and the Gulf of Mexico. But one of six cases reported to the CDC in 2018 occurred in Michigan.
Just because a state has detected EEE in mosquitoes or chickens doesn't mean the pests will transmit it to people. The virus is named for its prevalence in horses, after all.
Still, it's best to err on the side of caution. The CDC recommends residents of impacted areas go heavy on the repellant, avoid the outdoors after dark, and wear long sleeves and pants if they do venture outside.
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