DEERFIELD — The state Department of Public Health has announced that mosquitoes in Deerfield and Leyden have tested positive for West Nile virus.

A sample of mosquitoes taken in Deerfield on July 22 tested positive for the virus, which can cause illness ranging from a mild fever and headaches to more serious diseases like encephalitis or meningitis. In Leyden, a sample of mosquitoes tested positive for the virus on July 15.

Deerfield Health Agent Ned Saviski said that so far in 2025, no transmissions of the disease to humans have been detected, and there are a few precautions people can take to deter mosquito bites.

“The basic protections are wearing mosquito repellent with DEET, removing any standing water on your property, and wearing long-sleeve shirts and pants when you’re outside,” Saviski said. “The standing water is really important to remove. You don’t want to have buckets of standing water because that’s their breeding grounds.”

Saviski said avoiding West Nile virus does not require any special steps, and to avoid getting bitten by a mosquito carrying the disease, people should take the same precautions they would ordinarily take to avoid getting bitten, including limiting their time outside during peak mosquito hours of dusk to dawn; using insect repellant that contains DEET, permethrin, picaridin, KBR 3023, IR3535 or lemon eucalyptus oil; and putting screens on windows and doors to prevent mosquitoes from coming inside.

According to the Department of Public Health’s factsheet on West Nile virus, it was first detected in the United States in 1999. Between 2014 and 2023, 131 people have reportedly been infected with West Nile virus in Massachusetts, resulting in eight deaths.

According to the Pioneer Valley Mosquito Control District, “severe illness is very rare and roughly 80% of people infected with the virus do not develop any symptoms.” Symptoms such as muscle aches, tremors, fatigue and rash typically develop between two and 14 days after being bitten. While West Nile virus can infect people of all ages, people over the age of 50 are at higher risk of contracting a severe infection.

The Pioneer Valley Mosquito Control District’s recent report, detailing data collected the week of July 19, noted that to date this season, the district has collected 8,067 sample mosquitoes. The district found that while the most prevalent species of mosquito in Hampshire and Hampden counties is the Culex pipiens/restuans, a more common vector of the West Nile virus, in Franklin County the most prevalent species is the Coquillettidia perturbans.

In addition to West Nile virus, the Department of Public Health announced last week that a mosquito sample from Belchertown had tested positive for Eastern equine encephalitis (EEE). The sample, taken on July 21, marked the first identification of EEE in Massachusetts this season.

Despite the few positive samples, the Department of Public Health’s West Nile virus risk map at mass.gov/info-details/massachusetts-arbovirus-update still states that the risk of transmission is low in Franklin County. There have been a total of 41 positive samples across the state so far this year, with the highest levels of risk being in portions of Worcester, Middlesex and Suffolk counties.

Reach Madison Schofield at 413-930-4579 or mschofield@recorder.com.