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West Nile Virus Detected in Worcester Mosquito Sample

For Immediate Release: 7/13/2023 10:42 am

WORCESTER, Mass. – The Massachusetts Department of Public Health (MDPH) has announced that West Nile Virus (WNV) has been detected in mosquitoes collected from Worcester. At this time, no human cases have been detected, and the WNV risk level in Worcester remains Low.

In coordination with the Worcester Division of Public Health and Department of Inspectional Services, the Central Massachusetts Mosquito Control Project (CMMCP) will spray the designated area with truck-mounted equipment where the positive WNV insect was found, which can be viewed on the attached map. Application will occur after sunset on Tuesday, July 18, weather permitting. If conditions prevent spraying on that date, it will be rescheduled to Wednesday, July 19.

Residents may opt out of having their property sprayed during wide-area pesticide application by following instructions at Those wishing to opt out should do so as soon as possible to ensure they are excluded.

Residents are advised to observe the following precautions if their street is being sprayed:
• Close street-facing windows and turn off any “outside air” settings on air conditioners.
• Keep pets inside between sunset and midnight, and do not let children play near or behind truck-mounted applicators when they are in use.
• Remain inside during the application and for 15-20 minutes afterwards.
• Wash off any vegetables from home gardens after spraying and before consuming them.

Accidental exposure is not expected to cause any health concerns in most people, although anyone who suffers from chemical sensitivities or feels that spraying may aggravate a preexisting health condition should consult their physician and take special measures to avoid exposure if necessary. Accidental exposure to pets should also not cause a problem since the pesticide being used is similar to ones used for flea and tick control.

The City will also notify residents in the specific area to be sprayed via email, social media, and text. Residents interested in receiving these alerts should ensure that they are registered for ALERTWorcester ( with an up-to-date email and/or phone number.

To avoid mosquito bites and the diseases they can transmit, residents are encouraged to practice the “5 Ds:”

DRESS in long sleeves and pants when possible. Cover up during periods of mosquito activity.
DEET is an effective insect repellent. Always follow the label instructions.
DAWN & DUSK are mosquitoes’ most active periods.
DRAIN water from containers weekly. Avoid standing water, such as rain collecting in open bins, buckets, or toys.

Clothing treated with insect repellent is also available, and permethrin—the repellent commonly used—can be applied to treat clothing manually. Installing and repairing screens will help to keep mosquitoes out of homes.

West Nile Virus is most commonly transmitted to humans by the bite of a mosquito infected with the virus. While WNV can infect people of all ages, people over the age of 50 are at higher risk for severe infection. While most people infected with WNV will have no symptoms, some may experience fever, flu-like illness, and—in rare cases—more severe illness.

There were eight human cases of WNV in Massachusetts in 2022, although none occurred in Worcester County.

More information from MDPH, including all WNV and Eastern equine encephalitis (EEE) positive results in the state, can be found at, or by calling the MDPH Division of Epidemiology at 617-983-6800.

If an animal is suspected of having WNV or EEE, owners are required to report it to the Massachusetts Department of Agricultural Resources, Division of Animal Health by calling 617-626-1795, and to MDPH by calling 617-983-6800.


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