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Cambridge Mosquitoes Test Positive for West Nile Virus

Risk level remains "moderate" in Cambridge

August 7, 2021

State health officials reported on August 5 that a mosquito sample in Cambridge had tested positive for West Nile virus. The virus is usually transmitted to humans through the bite of an infected mosquito. 
Positive mosquito samples have also been detected locally in Arlington, Belmont, Boston, Medford, Quincy, Waltham, and Watertown. The risk of West Nile virus infection in Cambridge remains “moderate,” according to the Massachusetts Department of Public Health.
Heavy rains this summer have increased the population of Culex pipiens mosquitoes, the species responsible for most human infections. The Cambridge Public Health Department recommends that residents take added precautions to avoid mosquito bites and get rid of standing water on their property, including in containers and gutters.
Most human West Nile virus infections are mild, but a small number of people become very sick. People over 50 are at greatest risk for serious illness, especially those with weakened immune systems. No human cases of West Nile virus have been reported so far this season in Massachusetts. 
The East Middlesex Mosquito Control Project has larvicided over 6,700 storm drains on city streets in Cambridge. A second round of treatment will be completed this month.  Larvicide kills mosquito larvae before they can grow to adulthood. In addition, the crew has visited Cambridge wetlands areas multiple times this summer, and has applied larvicide as needed. Harvard and MIT have also treated storm drains on their campuses.
The best way to avoid West Nile virus is to prevent mosquito bites. Some tips:
  • Apply insect repellent when outdoors. Use a repellent with DEET, permethrin, picaridin, oil of lemon eucalyptus or IR3535. DEET products should not be used on infants under two months of age and should be used in concentrations of 30% or less on older children. Oil of lemon eucalyptus should not be used on children under three years of age. Follow the directions on the package.
  • 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.
  • Clothing can help reduce mosquito bites. Wearing long-sleeves, long pants, and socks when outdoors will help keep mosquitoes away from your skin.
  • Get rid of mosquito breeding sites in your yard. Mosquitoes lay their eggs in still water. Empty standing water from flower pots, buckets, barrels, and children’s pools. Change the water in pet dishes and replace the water in bird baths weekly. Drill holes in tire swings so water drains out.
  • Make sure that window and door screens fit tightly and are in good condition.
State and county information about West Nile virus and reports of West Nile virus activity in Massachusetts can be found on the state health department website.

For local West Nile virus updates and prevention tips, call the Cambridge Public Health Department at 617-665-3838 or visit the department's West Nile virus web page.

Suzy Feinberg, MPH
Public Information Officer

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Cambridge Public Health Department
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Cambridge, MA 02139
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617-665-3888 (fax)
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