The Department of Public Health (DPH) has announced that West Nile virus (WNV) has been detected in mosquitoes in Massachusetts for the first time this year. The presence of WNV was confirmed today by the Massachusetts State Public Health Laboratory in two mosquito samples collected on June 25 in the city of Quincy in Norfolk County.

State Public Health Officials Announce Season’s First West Nile virus-Positive Mosquito Samples

Residents urged to use bug spray when outdoors

BOSTON (July 2, 2024) – The Massachusetts Department of Public Health (DPH) today announced that West Nile virus (WNV) has been detected in mosquitoes in Massachusetts for the first time this year. The presence of WNV was confirmed today by the Massachusetts State Public Health Laboratory in two mosquito samples collected on June 25 in the city of Quincy in Norfolk County.

“This is about the time of year that we expect to start finding West Nile virus in mosquitoes,” said Public Health Commissioner Robbie Goldstein, MD, PhD. “It is an important 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.”

WNV is usually transmitted to humans through the bite of an infected mosquito. There were six human cases of WNV in 2023. No human or animal cases of WNV have been detected so far this year. No evidence of Eastern Equine Encephalitis (EEE) has been found so far this season. There were no human or animal cases of EEE in 2023.

While WNV can infect people of all ages, people over the age of 50 are at higher risk for severe disease. Most people infected with WNV will have no symptoms. When present, WNV symptoms tend to include fever and flu-like illness. In rare cases, more severe illness can occur.

“This is the beginning of our mosquito season in Massachusetts. From now on, we expect mosquito populations to increase, and we will start to see more of them carrying WNV,” said State Epidemiologist Dr. Catherine M. Brown. “Use 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 the mosquito-borne disease webpages on mass.gov so you know when and where WNV activity is occurring.”

Avoid Mosquito Bites

Apply Insect Repellent when Outdoors. Use a repellent with an EPA-registered ingredient (DEET (N,N-Diethyl-m-toluamide), permethrin, picaridin (KBR 3023), 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 the 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 either draining or discarding items that hold water. Check rain gutters and drains. Empty any 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 your 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 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.