Prolonged drought results in minimized EEE, West Nile Virus risk

  • Risk levels of West Nile Virus throughout Massachusetts. White indicates low, orange indicates moderate and red indicates high. Massachusetts Bureau of Infectious Disease and Laboratory Sciences

  • Risk levels of Eastern Equine Encephalitis (EEE) throughout Franklin County by town. Dark blue indicates remote risk and light blue indicates low risk. Massachusetts Bureau of Infectious Disease and Laboratory Sciences


Staff Writer
Published: 9/13/2022 9:36:57 AM
Modified: 9/13/2022 9:36:27 AM

The Pioneer Valley is facing little threat of Eastern Equine Encephalitis (EEE) and West Nile Virus this year, due to the lasting drought’s impact on the mosquito population.

Mosquitoes lay their eggs in pools of standing water, which need to stay calm for seven to 10 days so the eggs can gestate. Since the North quabbin region has been in a Level 3 Critical Drought for months, pools of standing water have not formed, meaning mosquitoes have been unable to lay eggs.

“The significant drought conditions that exist across the commonwealth have kept the populations of the Culex mosquito species that are most likely to spread (West Nile Virus) relatively small,” Public Health Nurse Lisa White wrote in a Franklin Regional Council of Governments Cooperative Public Health Service announcement.

According to the state Bureau of Infectious Disease and Laboratory Sciences and the Department of Public Health, towns in the North Quabbin region and Franklin County all have either remote or low risk of EEE. Additionally, all parts of Franklin County have a low risk of West Nile Virus. To view a map of town-by-town risk levels, visit

Carolyn Shores Ness, a member of the Deerfield Selectboard and chair of its Board of Health who helped create the Pioneer Valley Mosquito Control District in late 2016, explained Culiseta melanura mosquitoes — the mosquitoes that can carry West Nile Virus and EEE — never emerged this season.

“Hopefully now it is too late in the season,” she added.

However, Shores Ness said Culex pipiens, which can carry West Nile Virus, need less water. These mosquitoes are still being reported.

“It has been so dry, even though we had some water it got absorbed, so there is no standing water to get into tree cavities,” Shores Ness said. “Where we have issues now is in catch basins.”

Across the state, there have been four human cases of West Nile Virus, according to the Department of Public Health. All cases have been in Middlesex or Suffolk counties. The risk of human infection with West Nile Virus is moderate to high in the greater Boston area. However, no human EEE cases have been reported so far this year.

By comparison, in 2021, there were 11 human cases of West Nile Virus infection identified in Massachusetts, according to the Department of Public Health. While the virus can infect people of all ages, people over the age of 50 are at higher risk for severe disease.

Most people who are infected with West Nile Virus will have no symptoms. When present, symptoms tend to include fever and flu-like illness. In rare cases, more severe illness can occur.

The first West Nile Virus case found in a mosquito in the western part of the state was found on Tuesday in Hadley, Shores Ness said.

“Fortunately, we are in September,” she said. “We will have cool enough nights that they won’t take off.”

Normally, the season for West Nile Virus begins after July 4, and EEE begins at the end of July or the beginning of August. Since the calendar is beyond these times and the weather is getting colder, the county has passed the days where it could be hardest hit by the diseases, she said.

The Pioneer Valley Mosquito Control District is an active regional entity that tests for diseases in mosquitoes. The district continues to test mosquito samples and will notify the public if any concerns arise.

“We have had a mosquito district for a few years and it is paying off to know the threat locally,” Shores Ness said.

Still, Shores Ness emphasized the need to keep taking precautions.

“(Mosquitoes) are going to be reemerging in the next week or so because they had enough rain to make it possible,” she said, “so we need to keep following precautions.”

FRCOG’s public health nurses recommend residents protect themselves from mosquitoes by using insect repellent, avoiding being outside during peak mosquito hours (from dusk to dawn), and wearing long-sleeve shirts and pants.

Bella Levavi can be reached at or 413-930-4579.

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