Press Release  State health officials announce season’s second human case of West Nile virus in Massachusetts

Boston — The Massachusetts Department of Public Health (DPH) today announced the second human case of West Nile virus (WNV) in Massachusetts this year. The person is a male in his 70s who was exposed in Middlesex County in an area known to be at moderate risk.

The first WNV-positive mosquitoes in Massachusetts this year were announced on July 2 from mosquito samples collected in Quincy. There has been a total of 145 positive mosquito samples so far this year detected from Barnstable, Berkshire, Bristol, Dukes, Essex, Hampden, Middlesex, Norfolk, Plymouth, Suffolk, and Worcester counties. The risk of human infection with WNV is moderate in the Greater Boston area (Middlesex, Norfolk, and Suffolk counties) and in parts of Barnstable, Bristol, Essex, Hampden, Plymouth, and Worcester counties.

“Many parts of the country, including Massachusetts, are experiencing increasing WNV activity,” said Public Health Commissioner Robbie Goldstein, MD, PhD. “We are in the peak time of the year when most people are exposed to West Nile virus in Massachusetts. Residents should continue to take precautions to avoid mosquito bites.”

WNV is usually transmitted to humans through the bite of an infected mosquito. There were six human cases of WNV in 2023. The first WNV human case this year was announced on August 6 and was exposed in Hampden County. No animal cases of WNV have been detected so far this year.

“It is still summertime and the risk from WNV is going to be elevated for some time,” said State Epidemiologist Dr. Catherine M. Brown. “People should use mosquito repellent with an EPA-registered active ingredient, clothing to reduce exposed skin, and consider rescheduling outdoor activities that occur during the evening or early morning.”

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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