West Nile Virus Detected in Boston Mosquitoes for 1st Time This Summer

No human or animal cases of West Nile or Eastern equine encephalitis have been detected so far this year

Mosquitoes in Boston have tested positive for West Nile virus for the first time this season, Massachusetts health officials announced Thursday.

The presence of West Nile virus was confirmed in a mosquito sample that was collected July 3 in the city, the Massachusetts Department of Public Health said.

No human or animal cases of West Nile virus or Eastern equine encephalitis have been detected so far this year, health officials said. They also noted that there is no elevated risk level associated with Thursday's finding.

"The first West Nile virus positive mosquito sample is often identified in Massachusetts sometime during the last week of June or the first week in July," Department of Public Health State Epidemiologist Dr. Catherine Brown said in a statement. "Risk for human infection generally builds through the season with peak risk occurring in August."

Massachusetts set a record in 2018 with 49 human cases recorded in the state, the highest ever. The prior record was set in 2012 with 33 human cases.

West Nile is usually transmitted to humans through the bite of an infected mosquito. Anyone can get the virus, but people over 50 are at a higher risk for severe disease.

Most people who are infected show no symptoms, according to the DHP. If there are symptoms, they tend to include fever and flu-like illnesses. 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," said Brown. "The tools for prevention include using a mosquito repellent with an EPA-registered ingredient according to the directions on the label, wearing 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."

To learn more about how to protect yourself from the illness, visit or call the DPH Epidemiology Program at 617-983-6800.

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