Several counties in Massachusetts are spraying for mosquitoes in an effort to prevent the spread of the rare but deadly virus that causes Eastern equine encephalitis.
Aerial mosquito spraying in Bristol and Plymouth counties began on Thursday evening, according to a schedule posted on a state government website. The government decided to spray after mosquitoes in the area tested positive for EEE virus, meaning there was a “high risk” of human cases.
According to the Centers for Disease Control, EEE is a very deadly virus, killing roughly one-third of people who are infected.
“It is quite deadly,” said Andria Rusk, a research professor and member of the Global Health Consortium at Florida International University.
Fortunately, it’s exceedingly rare. There are only about seven cases each year on average in the U.S., the CDC says. In Canada, there has only been one human case, according to a report from Health Canada.
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Most cases occur in Florida, Massachusetts, North Carolina and New York state, according to the CDC.
Symptoms can resemble those of many viral infections, like flu, Rusk said. These include fever, headache, and possibly vomiting or diarrhea.
But what distinguishes an encephalitic disease like this are more subtle symptoms.
“There’s also mood changes, things like irritability, anorexia, drowsiness,” she said. “All of those are, to me, a trigger to go to the hospital.”
Patients can eventually develop disorientation, seizures and coma, according to the CDC.
Most deaths occur within two to 10 days of symptoms first appearing, Rusk said. Many survivors are also left with permanent brain damage as a result of the infection.
“It’s very likely that if you have the encephalitic form of the disease that you will have life-long disability with some pretty severe neurological sequelae (conditions resulting from disease),” Rusk said.
Some people even die years after the initial infection.
There is no treatment or vaccine for EEE, she said, so patients are mostly just given supportive care to help deal with their fever, stay hydrated and otherwise manage their symptoms.
Mosquitoes on the move
The EEE virus, like malaria or dengue, is transmitted by mosquitoes.
Generally, the mosquitoes bite an infected bird and pick up the virus as they feed, Rusk said. They then transmit the virus by biting a mammal like a horse or a human.
The virus can’t transmit between a horse and a human, or between two humans, as far as she knows, even if a mosquito bites them.
So far, the number of cases has been fairly steady, she said, fluctuating slightly due to wet weather that breeds more mosquitoes or other such factors.
But she expects that mosquito-borne diseases, including EEE, will become more common in the future.
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She said we’re seeing changes in mosquito-borne infectious diseases “with the territory of mosquitoes expanding with climate change, particularly in the southern United States and in Latin America.”
“I’m sure you guys are noticing now in Canada as well, particularly along your eastern coastline,” she said.
“Their territory expands, and when their territory expands you now have more people living in their territory. When you have more people living in their territory, you have more opportunity for human infection.”
While so far it hasn’t happened, “it wouldn’t surprise me at all that we see increases of cases of EEE, West EE (another mosquito-borne disease), along with everything else.”
Right now, she said, Canadians shouldn’t be worried about EEE, given its rarity. But, since mosquitoes can also carry West Nile virus and other diseases, it makes sense to keep bites to a minimum to prevent your chances of catching any mosquito-borne illness.
“Wear long sleeves, stay indoors during dawn hours and dusk hours because that’s when they bite,” she said. “Use DEET spray on your person and on your clothes if you’re ever going to be in wooded areas or if you’re going to be near fresh standing water.”
It’s also important to empty any containers of standing water, she said, such as inside plant pots, because mosquitoes only need a couple of cubic inches of water to lay eggs.