Mosquitoes will be active until the first hard frost, which occurs typically in early November, experts said. (Photo: Cambridge Public Health Department via Twitter)

Two mosquito samples collected from traps in West Cambridge and North Cambridge have tested positive for West Nile virus, the city’s Public Health Department reported Thursday, though the risk of infection statewide is deemed to be low.

Mosquitoes will be active until the first hard frost, which occurs typically in early November, the health department has said.

Positive mosquito samples have also been detected in Medford, Boston, Brookline, Framingham and Newton, health officials said.

“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, chief public health officer and director of the Department, in a press release. “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 East Middlesex Mosquito Control Project completed larviciding 5,976 storm drains on city and state property in Cambridge in June to kill mosquito larvae before they can grow to adulthood. The second round of treatment began July 22 and is expected to be completed in mid-August. Larvicide was also applied to wetlands in Danehy Park in August.

In 2018, there were 49 human cases acquired in Massachusetts, a record for the state in a single year.

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 – starting with fever and flu-like illness and extending to headache, high fever, neck stiffness, stupor, tremors, muscle weakness and paralysis.

Health officials advise residents to protect themselves against the virus by wearing mosquito repellent and pants and long-sleeved shirts outdoors. People should also consider staying indoors during times of high mosquito activity such as dawn and dusk, and keep screens in good repair. Residents can reduce the mosquito population by draining or eliminating containers that hold water, health officials say.

Information about the virus is on the Public Health Department website.


This post has been corrected to show two mosquitoes have tested positive for West Nile; no humans have been found to be affected.