Mosquitos seem less active this year, but state still urges caution to avoid illness

There’s a word that might seem apt for describing how the 2026 New Hampshire mosquito season has played out thus far, but you won’t hear it from Manchester Deputy Public Health Director Phil Alexakos.

“I’m not going to use the word that starts with a ‘Q,’ because we don’t do that in public health,” he joked in a phone call on Tuesday. “But it’s been a less-than-active season.” (The taboo word? “Quiet.”)

As of Sept. 10, there had been no detections this year of Eastern equine encephalitis virus, or EEE, in New Hampshire mosquitos, according to the New Hampshire Department of Health and Human Services. Detections of West Nile virus and Jamestown Canyon virus were lower than they had been in the past five years, a department spokesperson said.

The three pathogens are the major viruses of concern to humans that are known to circulate in New Hampshire’s mosquito population. In people, these pathogens can cause a range of symptoms, including potentially serious inflammation of the brain. One in three people who contract EEE dies.

Though rates have been lower than in recent years, this year’s detections of West Nile virus and Jamestown Canyon virus still call for precautions, officials said. 

Twenty-nine towns in New Hampshire, largely concentrated in the Seacoast and southeastern New Hampshire, have town-sponsored mosquito testing programs, according to DHHS. 

To surveil them for viruses, researchers use outdoor traps baited with alluring things like dry ice, which releases carbon dioxide gas like a breathing, blood-meal-bearing animal would; or a slurry of manure, hay, and water, which egg-bearing female mosquitos tend to love, Alexakos said.

The mosquitos are then removed from the traps, sorted by species, and sent for virus testing in clusters called “batches.” More than 5,000 batches have been tested so far this year in New Hampshire, according to the department.

Of those, seven batches had tested positive for Jamestown Canyon virus as of Sept. 10, according to DHHS. The insects came from traps in Exeter, Salem, Fremont, Kingston, Hampton, and Derry. Four batches had tested positive for West Nile virus, coming from Nashua, Kingston, and Rye.

No humans had tested positive for mosquito-borne illnesses in New Hampshire as of Sept. 10.

Similarly, no human cases have been reported so far this year in Vermont or Maine, according to the U.S. Centers for Disease Control and Prevention. Massachusetts has reported eight human cases of West Nile virus, according to the CDC. 

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A “great reset” will come with cooler weather, with the first hard frost subduing mosquitos for the year, according to Alexakos and DHHS. 

But for now, the risk remains — and according to DHHS, mid-September is often the peak of mosquito-borne illness activity.

The department urged residents to continue taking precautions against mosquito bites throughout the fall — such as wearing long sleeves and pants outdoors; using EPA-registered mosquito repellents; and staying indoors in evenings and early mornings, when mosquitos are most active, according to the department. Eliminating standing water can also reduce opportunities for mosquitos to breed.

Environmental shifts linked to climate change, such as rising temperatures, milder winters, and increasing rainfall, are linked to the expansion of diseases transmitted by vectors such as mosquitos and ticks.

New Hampshire has seen 20 reported cases of EEE in humans since 2003; 10 cases of West Nile Virus since 1999; and 23 cases of Jamestown Canyon Virus since 2011, according to the CDC.

It’s not clear why virus detection in New Hampshire mosquitos has been lower this season than in recent years, Alexakos said. If anything, he added, he anticipated this summer would have seen higher risk of West Nile virus, which is carried by mosquitos that thrive in warm and dry conditions. But a season could also theoretically be too dry, with less standing water for the bugs to breed, he said. 

Alexakos sees this year’s reports from New Hampshire municipalities as the tip of a larger iceberg. Manchester has run a surveillance program for mosquito-borne illnesses since 2000, shortly after a crow found dead in a city cemetery tested positive for West Nile virus in what was the first confirmed detection of the pathogen in New Hampshire. 

After that, for more than 25 years, city employees collected mosquitoes from traps across the city three to four times a week throughout the summer season. The program was reduced this year to one sample per week and handed off to a contractor, a move that Alexakos attributed to staff turnover and the labor-intensive nature of the project. 

But the data is still used for the same purpose, Alexakos said: Informing decisions about public safety, like deciding whether to initiate pesticide application when threat levels reach a certain benchmark (something Manchester has done on about six occasions over the years, according to Alexakos).

But even when the city was testing their three trapping locations multiple times weekly, the data was only a “snapshot,” he said. On a statewide scale, he pointed to the geographically limited spread of municipally run mosquito surveillance programs.

“If we have detections, I think that definitely gives information that we have more activity than we’re finding,” he said. “… If we don’t find things, that doesn’t mean we’re free and clear.”