State Health Officials Announce 12th Human Case of West Nile Virus in Massachusetts

14 WNV risk level raised to high in Milton and Quincy BOSTON (October 2, 2026) – The Massachusetts Department of Public Health (DPH) today announced the 12th human case of West Nile virus (WNV) this year. The individual is a woman in her 60s who was likely exposed in Norfolk County. As a result, the risk level for WNV in Milton and Quincy has been raised to high. Risk levels for WNV continue to be high in Boston, Brookline, Cambridge, Chelsea, Everett, Malden, Newton, Revere, Somerville, Watertown, and Winthrop. Most of the rest of the state is at moderate risk. The risk from WNV will continue until the first hard frost. DPH announced the state's first WNV-positive mosquitoes this year on June 16. Since then, 340 mosquito samples have tested positive for WNV so far this season from Barnstable, Berkshire, Bristol, Dukes, Essex, Franklin, Hampden, Hampshire, Middlesex, Norfolk, Plymouth, Suffolk, and Worcester counties. There have been no animal cases of WNV reported this year. Eastern equine encephalitis (EEE) continues to be detected in mosquitoes in Massachusetts this year. There have been 27 EEE-positive mosquito samples and no human or animal cases so far this year. Surveillance information, including case updates, is updated daily and posted online at the Massachusetts Arbovirus Update web page. DPH encourages everyone to use this online resource regularly to stay informed on risk levels in their community and around the state. 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 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 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, is available on the Arbovirus Surveillance Information web page, which is updated daily, or by calling the DPH Division of Epidemiology at 617-983-6800.