West Nile Virus Emerges as a 'High Risk' in Cambridge, Newton, Somerville, and Watertown


The Massachusetts Department of Public Health announced Thursday four new human cases of West Nile virus in the state this year, bringing the state’s total case count in 2020 to seven. Three of the four cases were exposed to the virus in Middlesex County, while the fourth case originated from Bristol County.

Due to the emergence of these cases, Cambridge, Newton, Somerville, and Watertown have been elevated to “high risk” for West Nile virus. Several other towns in Middlesex County, as well as three in Bristol County, have been elevated to “moderate risk.”

The three Middlesex County cases are all males — one in his 40s, one in his 60s, and one in his 80s. The fourth is a female under the age of 19.

The Cambridge Public Health Department issued its own statement on Friday, reporting that six of the seven human cases from this year were exposed or live in Middlesex County, but none are Cambridge residents.


According to the Centers for Disease Control and Prevention, West Nile virus is “the leading cause of mosquito-borne disease in the continental United States.” It is most commonly transmitted to humans by the bite of an infected mosquito.

The Commonwealth’s press release also stated that most people infected with the virus do not experience symptoms. If symptoms do manifest, they typically include fever and flu-like illness. People over the age of 50 are at a greater risk of severe illness.

In Cambridge’s press release, Claude A. Jacob, Chief Public Health Officer and director of the Cambridge Public Health Department, said that while mosquito populations are declining at the end of summer, a higher proportion of the populations are infected.

“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,” he said.

The Cambridge press release also reported the risk of mosquito-borne disease is present typically until early November, when the first hard frost usually occurs.

In its press release, the Cambridge Department of Public Health also included tips to avoiding mosquito bites, such as applying insect repellent when outdoors, being aware of peak mosquito-biting times, wearing protective clothing, removing mosquito breeding sites from yards, and making sure window and door screens are in good condition.

The press release also advised people to contact a nurse or doctor if they have symptoms of West Nile virus.

—Staff writer Taylor C. Peterman can be reached at Follow her on Twitter @taylorcpeterman.