West Nile Virus has been found in Boston mosquitoes. Here’s what to know.

"If you are going to be spending time outside, you need to be thinking about prevention and protection against mosquito bites."


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The mosquito-borne West Nile Virus was detected in a sample collected last week in Brighton, marking the first time the illness has appeared in Boston this year, the city’s Public Health Commission confirmed Tuesday.

“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,” the commission’s Interim Executive Director Rita Nieves said in a statement. “I encourage everyone to take the precautions necessary as they spend more time outdoors.”

According to health officials, many cases of West Nile Virus are asymptomatic, although some include fever and flu-like symptoms and in rare instances, more severe illness can take hold. The virus can infect people of all ages, with people over the age of 50 at higher risk. There is no vaccine or particular antiviral treatments for West Nile Virus.


The commission said no human or animal cases of the virus or of Eastern Equine Encephalitis virus, or EEE — which has been detected in samples taken from Franklin County this season — have been recorded in Boston this year.

West Nile Virus is commonly found in mosquitoes in the city around this time of year. Officials have detected it in Boston mosquitoes every year between June and November for the past two decades, but the commission notes that finding the virus in humans is rare.

No human cases were reported last year in Boston. In 2018, seven residents were diagnosed with the virus.

“It is typical to find West Nile Virus in mosquitoes in Boston at this time of year,” Health Commission Medical Director Dr. Jennifer Lo said in a statement. “There is not an elevated risk level in Boston right now. 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 mosquitos out of your home.”

Officials are also advising pet owners to speak with their veterinarians about approved mosquito repellents and vaccinations to prevent mosquito-borne illnesses.


West Nile Virus was detected in Massachusetts for the first time this year in two samples collected on July 7 in Belmont, according to the state Department of Public Health.

In 2019, the state saw five human cases of West Nile Virus, a significant decrease from the previous year when 49 cases marked a record high.

Last week, state officials said EEE was detected in mosquitoes sampled in Orange and Wendell earlier this month, kicking off what is expected to be another busy season for the rare illness after 12 human cases were reported and six people died last year during the commonwealth’s first outbreak in several years. Officials say EEE outbreaks typically last two to three years.

As of Wednesday, no human cases of West Nile Virus or EEE had been recorded in Massachusetts.


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