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West Nile Virus Found in Cambridge Mosquitoes

Risk level raised to "moderate" in Cambridge

July 31, 2015


View July 30 media release from the Massachusetts Department of Public Health

State health officials reported on July 30 that four mosquito samples in Cambridge had tested positive for West Nile virus. The mosquito samples were collected from traps in different parts of the city.

Positive mosquito samples were also reported in Boston, Brookline, Malden, Medford, Newton, Somerville, Waltham and several other Greater Boston communities.

Given that multiple samples of WNV-positive mosquitoes have been found in a relatively small geographic area and that hot, dry weather conditions are conducive to larger mosquito populations, the Massachusetts Department of Public Health has raised the risk level for human infections from “low” to “moderate” in 12 communities, including Cambridge.

“We are asking residents to remain vigilant and take added precautions this season by avoiding mosquito bites and removing stagnant water near their homes,” said Claude Jacob, the city’s Chief Public Health Officer and director of the Cambridge Public Health Department.

So far this summer, the East Middlesex Mosquito Control Project has treated over 5,500 storm drains in Cambridge with larvicide, which kills mosquito larvae before they can grow to adulthood.

West Nile virus is usually transmitted to people through the bite of an infected mosquito.

“Most human West Nile virus infections are mild, but a small number of people become very sick,” said Jacob. People over 50 are at greatest risk for serious illness, especially those with weakened immune systems.

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 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 at: www.mass.gov/dph/mosquito.

For local West Nile virus updates, call the Cambridge Public Health Department at 617-665-3848 or visit http://www.cambridgepublichealth.org/services/environmental-health/mosquito-borne-diseases/west-nile-virus.php.


Suzy Feinberg, MPH
Public Information Officer

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