SHREWSBURY — The Massachusetts Department of Public Health (DPH) confirmed Tuesday that West Nile virus (WNV) has been detected in the state for the first time this season, following testing of a mosquito sample collected in Shrewsbury on June 13.
“Mid-June is earlier than we typically first find West Nile virus-infected mosquitoes in Massachusetts. WNV activity is very difficult to predict in advance, which is why the mosquito surveillance system is so important,” said Public Health Commissioner Robbie Goldstein. “This early detection serves as a reminder that people should take steps to prevent mosquito bites. WNV can cause serious illness and there are simple things that you can do to protect yourself and your loved ones.”
Last year, the first detection occurred in late June. Nineteen human WNV cases were reported statewide in 2024, though none have been reported so far this year. There are also no current reports of Eastern equine encephalitis (EEE), a mosquito-borne virus that the DPH says occurs sporadically in Massachusetts, though four EEE cases were recorded in 2024.
“Even though this is a little early, it doesn’t necessarily mean we will have a bad season,” said State Epidemiologist Dr. Catherine Brown. “We recommend that everyone start using a mosquito repellent with an EPA-registered ingredient, wear clothing to reduce exposed skin, drain standing water, and repair window screens. We also encourage everyone to make it a habit to check our online risk level maps for updates on when and where WNV activity is occurring.”
WNV is transmitted to humans through the bite of an infected mosquito. Most people infected will not show symptoms, but the virus can cause fever and flu-like illness—and in rare cases, more serious complications, particularly for individuals over age 50.
Health officials recommend using EPA-registered repellents, avoiding outdoor activities at peak mosquito hours (dusk to dawn), wearing long sleeves and pants, and taking steps to reduce mosquito breeding areas around the home. Residents are urged to drain or discard containers that collect water—such as buckets, tires, flowerpots, and wading pools—and to change the water in birdbaths frequently. Rain gutters and outdoor drains should also be checked and cleared. In addition, homes should be mosquito-proofed by installing or repairing tightly fitting screens on windows and doors. Animal owners are advised to flush water troughs weekly during the summer, stable horses indoors overnight, and consult veterinarians about mosquito repellents and vaccines to protect against WNV and EEE.
For more information, including all WNV and EEE positive results, visit the Massachusetts Mosquito-Borne Diseases webpage or call the DPH Division of Epidemiology at 617-983-6800.
