A Bristol County man in his 70s has died of Eastern equine encephalitis, the 10th human case of the mosquito-borne illness and the second death attributed to it this year in Massachusetts, health officials announced Friday.
Officials declined to reveal when the man died, or give any other details about him, but said EEE was confirmed as the cause on Friday, deepening worries about the rare but deadly virus just as an unseasonably warm weekend promises to keep both people and mosquitoes active outdoors.
The man was a Freetown resident, according to the town’s website.
Fortunately, the warm weather also allows for aerial spraying, and portions of Bristol and Plymouth counties will be doused with pesticides starting Friday and through the weekend.
After that, cooler temperatures likely will prevent further spraying because mosquitoes won’t be sufficiently active to justify it, said Dr. Catherine Brown, state epidemiologist.
The state has done all it can, Brown said, and until the first hard frost kills the mosquitoes — probably some time next month — prevention lies in the hands of individuals.
“Aerial spraying is not a magic bullet. It cannot kill all the mosquitoes,” Brown said. “I’m really asking everyone to help us by being good about using mosquito repellent and using clothing to cover up, and in the highest risk areas avoiding outdoor activity between dusk and dawn.”
This year’s EEE outbreak is the largest since the 1950s, brought on by an unfortunate convergence of circumstances, Brown explained.
Prolonged periods of wet weather produced unusually large populations of mosquitoes, and scientists suspect the virus mutated slightly, making birds more susceptible to it.
“There just were so many mosquitoes this year, they were able to transmit it between the birds more effectively,” Brown said. “We ended up with large numbers of infected birds and large numbers of infected mosquitoes. That sets the stage for the possibility of spillover into humans.”
Typically, EEE-carrying mosquitoes bite only birds. But if enough birds are infected, mammal-biting mosquitoes may end up stinging an infected bird and then transmitting it to people.
In Massachusetts this year, the EEE virus was found in 421 mosquito samples, many of them from species capable of spreading the virus to people.
Bristol and Plymouth counties have long been hot spots for EEE because their abundant cedar swamps make an ideal home for the bird and mosquitoes species that carry the virus, Brown said.
In addition to the Bristol County man, a Fairhaven woman in her 50s died of EEE in late August. Additionally, a 5-year-old Sudbury girl became seriously ill with it.
Brown said that EEE is so rare there haven’t been enough cases to tell who is most susceptible. “Triple E infects people of any age,” she said. “We could hypothesize that both young children and older adults might be most susceptible because of their [weaker] immune systems.”
Of those who become ill with EEE, about 30 percent die. Most of the survivors suffer some kind of neurologic damage.
“Encephalitis means a swelling of the brain,” said Dr. Shira I. Doron, an infectious disease physician at Tufts Medical Center. “It can be rather unpredictable what the effects are depending on what parts of the brain are most affected.”
Encephalitis can result in persistent trouble with thinking, speaking, or moving. “It really differs from case to case,” she said. “Children tend to have better recovery because their neural pathways are still developing.”
The state has identified 35 communities now at critical risk, 40 at high risk, and 128 at moderate risk for the EEE virus in Massachusetts. Eight animals have also been stricken — seven horses and a goat. Details can be found at mass.gov/eee.
DPH has also confirmed a second human case of a milder mosquito-borne illness, West Nile virus, in a man in his 50s from Plymouth County.
Even in bad years, EEE remains rare, said Doron, the Tufts physician. “Overall one’s individual risk of developing this disease is still exceedingly low,” she said.
Still, it’s wise to take the recommended precautions
“Do those annoying things for a little while longer until that hard frost kills the mosquitoes,” Doron said, “and then we’ll have a peaceful winter.”