West Nile virus detected in Massachusetts ‘earlier’ than normal

West Nile virus has been detected in mosquitoes for the first time this year in the Bay State, according to the Department of Public Health.

The confirmed virus in a mosquito sample collected last week in Shrewsbury is “a little early,” DPH officials said.

“Mid-June is earlier than we typically first find West Nile virus-infected mosquitoes in Massachusetts,” Public Health Commissioner Robbie Goldstein said in a statement.

“WNV activity is very difficult to predict in advance, which is why the mosquito surveillance system is so important,” he added. “This early detection serves as a reminder that people should take steps to prevent mosquito bites. WNV can cause serious illness and 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 19 human cases of WNV in the Bay State last year. The first detection of WNV last year was in late June.

No human or animal cases of WNV have been detected so far this year.

At this time, there’s no evidence of Eastern equine encephalitis, another arbovirus that occurs sporadically in Massachusetts. There were four human cases of EEE in 2024.

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.

“Even though this is a little early, it doesn’t necessarily mean we will have a bad season,” said State Epidemiologist Catherine Brown.

“We recommend that everyone start using a mosquito repellent with an EPA-registered ingredient, wear clothing to reduce exposed skin, drain standing water, and repair window screens,” Brown added. “We also encourage everyone to make it a habit to check our online risk level maps for updates on when and where WNV activity is occurring.”

The hours from dusk to dawn are peak biting times for many mosquitoes. Consider rescheduling outdoor activities that occur during the evening or early morning in areas of high risk.

Wearing long sleeves, long pants, and socks when outdoors will help keep mosquitoes away from your skin.

Online risk level maps can be found here.

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