Press Release  State health officials announce risk level changes for West Nile virus in Massachusetts

Boston — The Massachusetts Department of Public Health (DPH) today announced that due to ongoing evidence of mosquitoes carrying West Nile virus (WNV), eight municipalities are now considered to be at high risk from the virus. This elevated risk level applies to Boston in Suffolk County and Abington, Brockton, East Bridgewater, Marion, Mattapoisett, Rochester, and Whitman in Plymouth County.

The first WNV-positive mosquitoes in Massachusetts this year were announced on July 2 from Quincy.  A total of 262 WNV-positive mosquito samples so far this year have been detected from Barnstable, Berkshire, Bristol, Dukes, Essex, Hampden, Middlesex, Norfolk, Plymouth, Suffolk, and Worcester counties. The risk of human infection with WNV is moderate throughout Bristol, Norfolk, and the rest of Plymouth County and in parts of Barnstable, Berkshire, Essex, Hampden, Middlesex, Plymouth, and Worcester counties.

“We are finding evidence of West Nile virus in mosquitoes in multiple parts of the Commonwealth,” said Public Health Commissioner Robbie Goldstein, MD, PhD. “While most people do not get severely ill from WNV, it is still important to take it seriously. People at greatest risk for severe disease from WNV infection include those over 60 years of age and people with certain medical conditions, such as cancer, diabetes, hypertension, kidney disease, and people who have received organ transplants.”

WNV is usually transmitted to humans through the bite of an infected mosquito. There were six human cases of WNV in 2023. There have been two human and no animal cases of WNV confirmed this year so far.

“The risk from WNV is pretty widespread this year,” said State Epidemiologist Dr. Catherine M. Brown. “In addition to recommending that people use mosquito repellent with an EPA-registered active ingredient and clothing to reduce exposed skin, check your window screens to be sure they don’t have holes and empty any containers that accumulate water around your yard.”

People have an important role to play in protecting themselves and their loved ones from illnesses caused by mosquitoes.

Avoid Mosquito Bites

Apply Insect Repellent when Outdoors. Use a repellent with an EPA-registered ingredient, such as DEET (N,N-diethyl-m-toluamide), permethrin, picaridin (KBR 3023), or oil of lemon eucalyptus (p-menthane-3,8-diol (PMD) or IR3535) according to the instructions on the product label. DEET products should not be used on infants under two months of age and should be used in concentrations of 30 percent or less on older children. Oil of lemon eucalyptus should not be used on children under three years of age.

Be Aware of Peak Mosquito Hours. The hours from dusk to dawn are peak biting times for many mosquitoes. Consider rescheduling outdoor activities that occur during evening or early morning in areas of high risk.

Clothing Can Help Reduce Mosquito Bites. Wearing long sleeves, long pants and socks when outdoors will help keep mosquitoes away from your skin.

Mosquito-Proof Your Home

Drain Standing Water. Mosquitoes lay their eggs in standing water. Limit the number of places around your home for mosquitoes to breed by draining or discarding items that hold water. Check rain gutters and drains. Empty unused flowerpots and wading pools and change the water in birdbaths frequently.

Install or Repair Screens. Keep mosquitoes outside by having tightly fitting screens on all windows and doors.

Protect Your Animals

Animal owners should reduce potential mosquito breeding sites on their property by eliminating standing water from containers such as buckets, tires, and wading pools – especially after heavy rains. Water troughs provide excellent mosquito breeding habitats and should be flushed out at least once a week during the summer months to reduce mosquitoes near paddock areas. Horse owners should keep horses in indoor stalls at night to reduce their risk of exposure to mosquitoes. Owners should also speak with their veterinarian about mosquito repellents approved for use in animals and vaccinations to prevent West Nile virus (WNV) and EEE. If an animal is suspected of having WNV or EEE, owners are required to report to the Department of Agricultural Resources, Division of Animal Health by calling 617-626-1795, and to the Department of Public Health by calling 617-983-6800.

More information, including all WNV and EEE positive results, can be found on the Arbovirus Surveillance Information web page at Mosquito-borne Diseases | Mass.gov, which is updated daily, or by calling the DPH Division of Epidemiology at 617-983-6800. 

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