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Jul 16
Boston Public Health Officials Announce Season’s First West Nile Virus-Positive Mosquito Sample

BOSTON - Friday, July 16, 2021 - ​The Boston Public Health Commission (BPHC) announced today that West Nile Virus (WNV) has been detected in mosquitoes in Boston for the first time this year. The presence of WNV was confirmed today by the Massachusetts State Public Health Laboratory in a mosquito sample collected on July 14, 2021 in Jamaica Plain. No human or animal cases of WNV or Eastern Equine Encephalitis (EEE) have been detected so far this year in the City of Boston. Although there is no elevated risk level or risk-level change associated with this finding, BPHC advises residents to prevent mosquito bites and to mosquito-proof their homes.

“It is typical to find West Nile Virus in mosquitoes in Boston at this time of year,” said Dr. Sarimer Sanchez, Director of the Infectious Disease Bureau at the Boston Public Health Commission. “However, it is also that time of year when many of us will be spending time outdoors, enjoying summertime in New England. When you or your family are outside, it is important that you take steps to prevent mosquito bites. That includes using an approved mosquito repellent, draining standing water from your yard and repairing window screens to keep mosquitos out of your home.”

West Nile Virus (WNV) is a rare but serious disease most often spread to people by the bite of an infected mosquito. WNV has been detected in Boston mosquitoes during the summer and fall months (June – November) every year since 2000, but WNV in people is rare. In 2020 and 2019, there were no human cases of WNV infection diagnosed in Boston residents. In 2018, there were seven human cases of WNV infection diagnosed in Boston residents.

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.  There is no vaccine or specific antiviral treatments for West Nile Virus infection. The most effective way to avoid WNV is to take measures to prevent mosquito bites.

Mosquitoes in Boston are most active from dusk to dawn during the months of July to September, but mosquitoes can spread disease until the first hard frost (as late as November). The risk can be reduced by using insect repellent when outdoors, especially from dusk to dawn and, when possible, wearing long-sleeved shirts and pants. Residents should also make sure that their window and door screens are in good repair to prevent mosquitoes from getting inside. To help prevent mosquitoes from breeding, BPHC advises residents to empty standing water from flowerpots, gutters, buckets, pool covers, pet water dishes, discarded tires, and birdbaths on a regular basis.

Preventing Mosquito Bites:

Use Mosquito repellent

  • Use repellents containing DEET, oil of lemon eucalyptus, picaridin or IR3535. 

  • Always read the directions on the label.

  • Apply DEET to exposed skin (avoid eyes and mouth) and on clothes, but not on open cuts or wounds. 

  • After going inside, wash off repellent with soap and water. If the product has been applied directly to clothing, wash it before wearing again.

  • Do not use DEET concentrations of more than 30%.

  • Do not let children apply repellents themselves. Avoid children's eyes, mouth, or hands and use them cautiously around ears.

  • Do not use DEET on infants under two months of age (mosquito netting can be used over infant carriers) or oil of lemon eucalyptus on children under 3 years of age.

  • Use only repellents approved for use on animals on pets.

  • Wear protective clothing such as long-sleeved shirts, long pants and socks whenever possible. Tuck your shirt into your pants to keep mosquitoes from going under your clothes.

  • Mosquitoes lay their eggs in standing water, so it is important to make sure items around your home do not collect any water. It only takes one week for mosquito larvae living in water to grow into biting adults. Turn over unused flowerpots, buckets, wheelbarrows and garbage cans; remove leaves and other debris that can clog gutters and trap water; dispose of or cover old tires; and cover swimming pools when not in use.

  • Make sure window and door screens do not have holes in them. Screens in good condition will help prevent mosquitoes from getting inside your home.

  • Pet owners should speak with their veterinarian about mosquito repellents approved for use in animals and vaccinations to prevent WNV and EEE.

Citywide Prevention Efforts:

BPHC partners with the Suffolk County Mosquito Control Project (SCMCP) to protect Boston residents from mosquito-borne illnesses and to control the mosquito population in certain areas of Boston. SCMCP collects mosquito samples in traps every week during the summer and fall. Those mosquito samples are tested to see if WNV or EEE are present. Mosquito control measures are also implemented during the summer and fall months. Wetlands, storm drains and other areas around the city are treated to limit the number of mosquitoes by killing mosquito larvae.

In April of 2021, there were sprayings in Hyde Park and West Roxbury. For more information about the sprayings, reach out to SCMCP at 781-899-5730. For a full list of any upcoming spraying, please visit

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