ERVING — The state Department of Public Health has detected West Nile virus in a sample of mosquitoes from Erving, the town’s Board of Health announced Tuesday.
The Board of Health’s announcement on Erving’s town website shared that this is the first West Nile virus case detected in town this year. The virus was not found in Erving in 2024.
According to the Department of Public Health’s dashboard tallying positive West Nile virus samples, Erving’s sample was dated Sept. 14. Positive samples have also been detected in Northfield, Leyden, Bernardston, Rowe, Shelburne, Sunderland and Deerfield.
This data was provided to the state by the Pioneer Valley Mosquito Control District, which collects samples of mosquitoes in member towns in Franklin, Hampshire and Hampden counties. The district also provides management services tailored to each municipality to reduce mosquito-borne illnesses and mosquito nuisance.
John Briggs, director of the Pioneer Valley Mosquito Control District, said this year represents the highest level of West Nile virus the district has seen in the Pioneer Valley since it began testing in 2020.
“The only positive West Nile virus sample we had was in 2023, in Deerfield, that we had collected in our surveillance trap,” Briggs said on Thursday. “This year, we have 16 positive samples from Franklin County.”
Across the district’s 24 member municipalities, the total count is 53 positive samples. The testing pools collected range from five to 50 mosquitoes.
Briggs said it is hard to pinpoint an exact cause of the increase in West Nile virus in Franklin County and across the Pioneer Valley this year, but the weather has been favorable for Culex pipiens, the main vector species for the virus.
“They are considered a container species that will utilize catch basins or storm drains, green swimming pools, buckets, tarps, discarded tires and bird baths,” Briggs said about the mosquitoes’ breeding grounds.
The spring 2025 newsletter from the Pioneer Valley Mosquito Control District stated that the National Oceanic and Atmospheric Administration’s prediction of rainfall and above-average temperatures from May through July could mean an active year for mosquitoes.
Notably, higher cases of West Nile virus are typically found in urban zones. Briggs said this increase in cases in rural areas, especially in the northern portion of Franklin County, requires some detective work to better understand. Locations with beaver dams, or spots with stagnant water, are areas that have been investigated for cases in the county.
To help better educate the public on the health risks mosquitoes carry, Briggs said the district works with local boards of health and provides resources online for monitoring. The main at-risk populations for West Nile virus are people over the age of 50, and severe illness is rare. Roughly 80% of people who become infected do not develop symptoms. There have not been any human cases of West Nile virus in Franklin County this year.
The mosquitoes start to die off or hide away for the winter after a hard frost, not as the temperatures begin to drop off in the evenings in the late summer and early fall. This is why Briggs urges people not to let their guard down, even if the daytime and evening temperatures start to decline.
“Those mosquitoes are still alive, and all it takes is a warmer day for them to become active,” he explained. “This is the time when we’re going to see most human cases around September, late August. September is usually around the time that we start to see most human cases. So folks should definitely not let their guard down.”
To monitor cases of West Nile virus, Briggs advises people should visit the Pioneer Valley Mosquito Control District website at pvmcd.org.