State Public-health Officials Announce Presence of West Nile Virus

BOSTON — The Massachusetts Department of Public Health (DPH) announced last week 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 that was collected July 3 in Boston. No human or animal cases of WNV or eastern equine encephalitis have been detected so far this year.  There is no elevated risk level or risk-level change associated with this finding. 

“The first WNV positive mosquito sample is often identified in Massachusetts sometime during the last week of June or the first week in July,” said DPH State Epidemiologist Dr. Catherine Brown. “Risk for human infection generally builds through the season, with peak risk occurring in August.”

West Nile is usually transmitted to humans through the bite of an infected mosquito. 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 West Nile 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,” Brown said. “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.”