Nine counties in Michigan where an unusually high number of horses have contracted a rare and deadly mosquito-borne virus have been told to shut down outdoor activities after dusk to limit human exposure, according to public health officials.
At least one suspected human case has been recorded, officials said Wednesday.
About a third of people who become ill from the Eastern Equine Encephalitis virus, or EEEV, will die, according to the Centers for Disease Control and Prevention. Those who do survive often experience long-lasting effects and can “die within a few years.”
“As animal cases continue to grow, the risks to people increase as well,” Dr. Joneigh Khaldun with the Michigan Department of Health and Human Services said in a news release. “People get EEE the same way horses do — from the bite of an infected mosquito — so a case in a horse means people in that area are also at risk.”
There have been 22 confirmed cases of the virus in horses — double the number of animal cases from the same time last year — across 10 counties in Michigan as of Wednesday, officials said.
Khaldun said limiting outdoor activities around dusk “when mosquitoes are most active” could help prevent human infection.
The health department issued a recommendation Friday encouraging counties affected to cancel or postpone events at night, particularly those involving children, who are at greater risk if they become infected.
“This would include events such as late evening sports practices or games,” Friday’s news release states. “The MDHHS recommendation is being made out of an abundance of caution to protect the public health, and applies until the first hard frost of the year.”
Cases of EEEV
The U.S. records an average of 11 EEEV cases in humans every year, according to the CDC.
In 2019, however, there were 38 cases — including 12 in Massachusetts and 10 in Michigan. Khaldun said things like temperature and rainfall “are thought to play a role” in higher infection rates.
Transmission of the virus often occurs near freshwater hardwood swamps on the Atlantic or Gulf Coast as well as in the Great Lakes region, according to the CDC.
Anyone who works outdoors or engages in recreational activities near those types of environment are reportedly at risk of infection. People older than 50 and younger than 15 also “seem to be at greatest risk for developing severe disease when infected with EEEV,” according to the CDC.
Those diseases include meningitis and encephalitis, also known as a brain infection or swelling of the brain, but can manifest differently depending on the age of the person infected.
Some infected people are asymptomatic. Those who do show symptoms may have a fever, chills, general discomfort and joint or muscle pain for up to two weeks, the CDC says.
“Most people recover completely when there is no central nervous system involvement,” according to the agency.
But the virus can bring on neurological disease resulting in encephalitis. Those symptoms include fever headache, vomiting, diarrhea, seizures, behavioral changes, drowsiness and coma, the CDC says.
Roughly 33% of people who get encephalitis from EEEV will die from it anywhere from two to 10 days after symptoms begin, according to the federal agency.
“Of those who recover, many are left with physical or mental sequelae, which can range from mild brain dysfunction to severe intellectual impairment, personality disorders, seizures, paralysis, and cranial nerve dysfunction,” the CDC says.
There is no vaccine or cure for EEEV.
How to avoid mosquito bites
Health officials recommend wearing protective clothing and staying indoors when mosquitoes are active.
They also suggest:
Applying insect repellent that uses DEET to skin and clothing
Keeping screens on your doors and windows
Emptying water from possible mosquito breeding sites, such as buckets, kiddie pools, and old tires
Using nets and fans when eating outdoors