The West Nile virus risk level has been raised to moderate in 12 communities, including Boston, the Massachusetts Department of Public Health said Thursday. The other communities include Brookline, Cambridge, Chelsea, Everett, Malden, Medford, Melrose, Newton, Revere, Somerville and Watertown, health officials said. The change is in response to multiple West Nile virus-positive mosquitoes being found in a relatively small geographic area of the state that has historically had significant virus activity, health officials said.

“These findings, combined with the current weather patterns (warm/hot and relatively dry) indicate that human risk from WNV has increased,” the department said. “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.”

No human cases of West Nile virus or Eastern equine encephalitis have been detected so far this year. While West Nile virus can infect people of all ages, those over 50 are at higher risk for severe symptoms. West Nile virus is usually transmitted to humans through the bite of an infected mosquito. Most people infected with West Nile virus will have no symptoms. When present, West Nile virus symptoms tend to include fever and flu-like illness. In rare cases, more severe illness can occur.

In 2014, there were six human cases of West Nile virus infection identified in Massachusetts.

Source WCVB-Boston