Massachusetts DPH Confirms Season’s First Mosquito Sample Positive for West Nile Virus

BOSTON — The Massachusetts Department of Public Health (DPH) announced that West Nile virus (WNV) has been detected in mosquitoes in Massachusetts for the first time this year. The presence of WNV was confirmed by the Massachusetts State Public Health Laboratory in a mosquito sample collected on June 29 in the town of Medford in Middlesex County. No human or animal cases of WNV or eastern equine encephalitis (EEE) have been detected so far this year. There is no elevated risk level or risk-level change associated with this finding.

“The first WNV-infected mosquito of the season is always a signal that it is time to start taking steps to avoid mosquito bites,” said Margret Cooke, acting DPH commissioner. “WNV is part of summer in Massachusetts, and … it is important to remember that, while WNV can cause serious illness, there are simple things that you can do to protect yourself and your loved ones.”

WNV is usually transmitted to humans through the bite of an infected mosquito. There were eight human cases of WNV in 2020. In 2018, there were 49 human cases of WNV infection acquired in Massachusetts — the greatest number of cases the Commonwealth has ever had in a single year. While WNV can infect people of all ages, people over age 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.

“These simple actions can help protect you from mosquito bites and the diseases they can cause,” said Dr. Catherine Brown, state epidemiologist. “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.”