Longtime Newbury residents cannot remember the last time their North Shore town was on high alert for risk of infection from mosquito-borne Eastern equine encephalitis, prompting cancellation of outdoor activities at night.
In Cambridge, health officials have discussed spraying pesticide for the first time in 12 years to kill mosquitoes carrying West Nile virus after two residents were recently sickened by the disease.
Twice this season, planes have blanketed several Southeastern Massachusetts towns with pesticide to beat back Eastern equine encephalitis-infected mosquitoes detected in that region weeks earlier than normal.
And in the Berkshires, a woman in her 70s has been hospitalized with West Nile, the third Massachusetts resident this summer diagnosed with the disease, state health officials said Friday.
In Massachusetts and across the country, unprecedented levels of disease-carrying mosquitoes are spreading fears and challenging communities not used to grappling with such a foe.
“In the past two weeks, we have received 130 calls from residents about mosquitoes; it’s quite unusual,” said Sharon Cameron, director of public health in Peabody, where on Friday disease trackers reported finding a batch of mosquitoes infected with the Eastern equine encephalitis virus, commonly known as EEE.
It is the first time in at least seven years that EEE-bearing mosquitoes have been pinpointed in Peabody, a city of 51,000 north of Boston. And because they are the type known to occasionally bite people, there is heightened concern, Cameron said.
The city has sprayed twice in recent weeks to tamp down mosquitoes because of large numbers found with West Nile, and officials were preparing Friday night to go out, again.
Such battles are being waged nationwide this summer, as a record number of West Nile infections has been reported by the federal Centers for Disease Control and Prevention: more than 1,100. Already, there have been 41 deaths.
Disease specialists are unsure what is fueling the unprecedented numbers, but some speculate that the unusually warm winter might have accelerated reproduction of the insects and viruses in the environment.
The science is perplexing, because conditions that are believed to foster West Nile virus-bearing mosquitoes — hot and dry — are the opposite of the wet weather thought to be prime for EEE-infected insects, said Richard Pollack, an infectious disease instructor at Harvard School of Public Health.
“The textbook conditions don’t seem to be holding up,” Pollack said. “We have to rethink some of what’s going on. There’s more that we don’t know than we do know.”
In Reading, for instance, a batch of West Nile infected mosquitoes was found earlier this week, while mosquitoes with EEE, a type known for biting people, were collected there earlier this month.
Most people infected with West Nile have no symptoms, but those with EEE often suffer severe complications, and as many as 30 percent die.
The EEE virus discovery in Reading heightened anxieties because the virus has rarely been detected north of Boston. But in the past two weeks, human-biting mosquitoes infected with the virus have also been found in nearby Lynnfield and Peabody.
A few towns north of there, a horse in Georgetown had to be euthanized after being sickened by Eastern equine, a sign that human-biting mosquitoes are probably in that town, health officials said. The region is home to many horse farms, where owners typically vaccinate their animals against the virus — no human vaccine is available — but the case has prompted jitters, said Holly Willard, a veterinarian and the town’s animal inspector.
“A lot of horse owners keep their horses outside day and night when the weather is nice, but I think there will be more putting their horses in between dusk and dawn, rather than leave them outside,” Willard said.
Mosquitoes are most active between dusk and dawn, a point health officials stress when urging people to take precautions against being bitten, including using insect repellent, covering exposed skin outside, and limiting outdoor activities at night.
The horse case prompted the state Public Health Department to raise the risk for more EEE infections to critical in Georgetown and to high in five nearby communities, including Newbury.
“Where does it end?” said Joseph Story, a lifelong Newbury resident and chairman of the Board of Selectmen. The town’s Pop Warner football league promptly decided to end practices a half-hour early and sent notices to parents saying they should not send children to sessions if they have qualms about mosquitoes, Story said.
With the Great Marsh, New England’s largest salt marsh, snaking through Newbury, many residents are regularly drawn to the water for boating, clamming, and other activities.
“Our Board of Health sent out a recommendation that after-dusk activities be curtailed,” Story said, “but our commercial clam diggers aren’t governed by dusk to dawn. They are governed by the tides.”
In Cambridge, city officials are discussing canceling nighttime outdoor activities, the first time that has happened since 2000, when West Nile arrived here and little was known about how it was spread, said Sam Lipson, the city’s director of environmental health.
As West Nile makes more and more people sick in Massachusetts and across the country, disease trackers fear the infections may be a harbinger.
The virus has the ability to mutate and adapt, Dr. Robert Haley of the University of Texas Southwestern Medical Center, wrote in an article Friday in the Journal of the American Medical Association. West Nile virus, he said, “is likely to remain a serious threat into the foreseeable future.”
Kay Lazar can be reached at firstname.lastname@example.org.