giant mosquito on car

Mosquitos are nothing new to the region. This large specimen was spotted in 2010. (Photo: Chris Devers)

State health officials are observing a July tradition: raising the risk of West Nile virus infection to “moderate” from “low” after the collection of mosquitos testing positive for the disease.

A mosquito sample from a trap in West Cambridge tested positive for West Nile virus Thursday, health officials said, and positive mosquito samples have also been detected in Belmont and Boston. The risk level was raised Monday in those communities as well as in Brookline, Newton and Watertown.

“We are advising residents to start taking precautions to avoid mosquito bites, such as wearing repellent or protective clothing in the evening, fixing screens and eliminating standing water on their property,” said Claude Jacob, the Cambridge’s chief public health officer and director of the Cambridge Public Health Department.

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

Last year, when there were 16 human cases of West Nile in Massachusetts, the raising of the risk level came July 28 after two West Nile-positive mosquitos were trapped in West Cambridge; in 2015, the risk level was hiked July 31 after the trapping of four affected mosquitos.

The East Middlesex Mosquito Control Project is in the process of treating the city’s storm drains with larvicide, which kills mosquito larvae before they can grow to adulthood, health officials said.

The best way to avoid West Nile is to prevent mosquito bites by applying insect repellent when outdoors; rescheduling outdoor activities in the evening or early morning, which are peak biting times; wearing long sleeves, long pants and socks when outdoors; making sure window and door screens fit tightly and are in good condition; and getting rid of mosquito breeding sites in the yard. Mosquitoes lay their eggs in still water such as in flower pots, buckets, barrels and children’s pools, so it’s best to change the water in pet dishes and replace the water in bird baths weekly, and to drill holes in tire swings so water drains out.


Please consider making a financial contribution to maintain and improve Cambridge Day. Click here to see how.