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West Nile Virus Detected in Grafton Hill Mosquito Sample for Second Time

For Immediate Release: 9/20/2023 3:25 pm

WORCESTER, Mass. – The Massachusetts Department of Public Health (MDPH) announced that West Nile Virus (WNV) has been detected in mosquitos for a second time collected in a trap on the western side of the Grafton Hill neighborhood. The Central Massachusetts Mosquito Control Project (CMMCP) has scheduled a truck-mounted pesticide application to the designated area (see attached map) for after sunset on Thursday, Sept. 21, weather permitting.

West Nile Virus and Eastern equine encephalitis (EEE) have both been detected in Worcester County mosquito samples this summer, and the risk level for WNV was elevated to Moderate in Worcester. There have been three positive cases of WNV in humans in Massachusetts in 2023.

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.

Residents may opt out of having their property sprayed during wide-area pesticide application by following instructions at

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.

While WNV can infect people of all ages, people over the age of 50 are at higher risk for severe infection. Most people infected with WNV will have no symptoms, although some may experience fever, flu-like illness, and—in rare cases—more severe illness. More information from MDPH, including all WNV and 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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