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West Nile Virus Infection Risk in Cambridge Raised to High

September 11, 2020

The Massachusetts Department of Public Health (MDPH) announced on Sept. 10 that the risk of West Nile virus infection in Cambridge, Watertown, Somerville, and Newton had been raised to “high.” 
The “high risk” designation was tied to the announcement that three of the four new human West Nile virus cases reported on Sept. 10 were exposed in Middlesex County, based on case investigation interviews. Of the seven human cases reported this year, six were exposed or live in Middlesex County. None are Cambridge residents.
Most West Nile virus activity this season has occurred in an area around Boston and includes parts of Norfolk, Middlesex, and Essex counties, according to MDPH. Positive mosquito samples were first reported in Cambridge on September 3. Infected mosquitoes were detected earlier in the season in nearby communities, including Arlington, Belmont, Boston, Brookline, Newton, and Watertown. 
“At the end of summer, mosquito populations are declining, but a higher proportion of mosquitoes are infected,” said Claude A. Jacob, Chief Public Health Officer and director of the Cambridge Public Health Department. “For this reason, residents should continue to take the precautions to protect themselves from mosquito bites when outside in the evening and early morning hours.” 
The risk of mosquito-borne disease remains until the first hard frost, which is typically in early November in Massachusetts.
Most human West Nile virus infections are mild with no symptoms, but a small number of people become very sick with encephalitis or meningitis. People over 50 and those with weakened immune systems are at greatest risk for severe illness. Symptoms include fever and flu-like illness. More severe symptoms include headache, high fever, neck stiffness, stupor, tremors, muscle weakness, and paralysis.
If you think you have symptoms of West Nile virus, contact your doctor or nurse.
The easiest and best way to prevent mosquito-borne disease is to avoid mosquito bites. Some tips:
  • Apply insect repellent when outdoors. Use insect repellent containing DEET, picaridin, oil of lemon eucalyptus, or IR3535. Follow the directions on the package. 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.
  • 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.
To find out the risk of West Nile virus in individual Massachusetts cities and towns, see: mass.gov/info-details/massachusetts-arbovirus-daily-update.
Additional information about mosquito-borne disease can be found on the state health department website at mass.gov/mosquito-borne-diseases.
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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