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West Nile virus found in Boston mosquitoes for first time in 2020

A biologist examined a mosquito, the main carrier of West Nile virus.
A biologist examined a mosquito, the main carrier of West Nile virus.Rick Bowmer/Associated Press

West Nile virus has been detected in mosquitoes in Boston for the first time this year, though no cases in humans or larger animals have yet been found, the Boston Public Health Commission said Tuesday.

The state’s public health laboratory confirmed that a sample of mosquitoes collected in Brighton on Thursday tested positive for the virus, according to the commission.

There is no vaccine for the rare mosquito-borne virus. It can cause fever and other flu-like symptoms, which are more likely to be serious in people over age 50, though most people infected do not get sick, the commission said in a statement.

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“While much of the attention right now is on the COVID-19 pandemic and slowing the spread of this virus, we cannot lose sight of the importance of protecting ourselves against mosquito bites and the serious diseases they may carry,” Rita Nieves, interim executive director for the commission, said in the statement. “I encourage everyone to take the precautions necessary as they spend more time outdoors.”

So far there is no evidence that the coronavirus can be spread by mosquitoes or other biting insects, the commission said. The coronavirus is mostly spread from one person to another.

To avoid infection with West Nile virus, public health officials recommend using insect repellent when spending time outside, especially between dawn and dusk, when mosquitoes are most active, and wearing long sleeves and pants if possible.

They also recommend checking door and window screens to make sure homes are secure from mosquitoes and eliminating standing water outside the home, where mosquitoes can lay eggs.


The virus has been found in mosquitoes in Boston every year since 2000, but human cases are rare, the commission said. No cases were found in humans last year, but in 2018, seven Boston residents were diagnosed with West Nile virus.

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“There is not an elevated risk level in Boston right now,” Dr. Jennifer Lo, medical director for the commission, said in the statement. “However, if you are going to be spending time outside, you need to be thinking about prevention and protection against mosquito bites. That includes using an approved mosquito repellent, draining standing water from your yard and repairing window screens to keep mosquitoes out of your home.”


Jeremy C. Fox can be reached at jeremy.fox@globe.com. Follow him on Twitter @jeremycfox.