State Raises Risk Level for West Nile Virus After Mosquitoes Test Positive

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After numerous mosquitoes tested positive for West Nile Virus in communities around Watertown, state officials raised the risk for the for the disease.

The Massachusetts Department of Public Health (DPH) announced that they have raised the West Nile Virus (WNV) risk level to “moderate” in Boston, Brookline, Cambridge, Chelsea, Everett, Malden, Medford, Melrose, Newton, Revere, Somerville, and Watertown.

This change is due to multiple WNV-positive mosquitoes being found in a relatively small geographic area of the Commonwealth that has historically had significant WNV activity, according to the announcement. These findings, combined with the current weather patterns (warm/hot and relatively dry) indicate that human risk from WNV has increased.


The positive tests came from mosquitoes in Cambridge, Newton, Waltham and Boston, according to the Mass DPH website.

Although not all of the communities identified have had mosquito positives yet, historic evidence shows that WNV activity tends to follow similar patterns throughout all these communities, the announcement said.

No human cases of WNV or Eastern Equine Encephalitis (EEE) have been detected so far this year.

“These findings serve as an important reminder of the need for personal protection from the threat of mosquito-borne illness,” said DPH State Public Health Veterinarian Dr. Catherine Brown. “Protection includes using a mosquito repellent with an EPA-approved ingredient according to the directions on the label, using clothing to reduce exposed skin when weather permits, draining standing water to prevent mosquito breeding and repairing window screens to keep mosquitoes out of your home.”

WNV is usually transmitted to humans through the bite of an infected mosquito. In 2014, there were six human cases of WNV infection identified in Massachusetts, according to the Mass. DPH. While WNV can infect people of all ages, people over the age of 50 are at higher risk for severe disease. Most people infected with WNV will have no symptoms. When present, WNV symptoms tend to include fever and flu-like illness. In rare cases, more severe illness can occur.

People have an important role to play in protecting themselves and their loved ones from illnesses caused by mosquitoes.

For tips from the Mass. DPH for avoiding mosquito bites, click here.

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