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West Nile Virus Found in Cambridge Mosquitoes

August 16, 2019

State health officials reported on August 15 that two mosquito samples in Cambridge had tested positive for West Nile virus. The mosquito samples were collected from traps in West Cambridge and North Cambridge. 
Positive mosquito samples have also been detected locally in Boston, Brookline, Framingham, Medford, and Newton.

According to the Massachusetts Department of Public Health, the risk of West Nile virus infection in Greater Boston and most of the Commonwealth remains low.
“While this has been a mild West Nile virus season so far, the greatest risk of infection in Massachusetts is in August and September,” said Claude Jacob, the city’s Chief Public Health Officer and director of the Cambridge Public Health Department. “Residents should take added precautions to avoid mosquito bites, such as wearing repellent or protective clothing in the evening, fixing screens, and eliminating standing water on their property.” 
The virus is usually transmitted to humans through the bite of an infected mosquito. 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.
In 2018, there were 49 human cases acquired in Massachusetts, the highest number of laboratory-confirmed West Nile virus cases ever recorded in the state in a single year.
The East Middlesex Mosquito Control Project completed larviciding 5,976 storm drains on city and Department of Conservation and Recreation (DCR) property in Cambridge on June 17.  Larvicide kills mosquito larvae before they can grow to adulthood. The second round of treatment began on July 22 and is expected to be completed in mid-August. Larvicide was applied to wetlands in Danehy Park in August. 
The city has also posted mosquito advisory signs in designated parks and playgrounds.
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/mosquito-borne-diseases and http://www.mosquitoresults.com

For local West Nile virus updates, call the Cambridge Public Health Department at 617-665-3838 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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