Press Release  State health officials announce first animal case of WNV in Massachusetts (Corrected)

Boston — The Massachusetts Department of Public Health (DPH) today announced the first confirmed case of West Nile virus in an animal this year. A goat was exposed to WNV in Lunenburg in Worcester County. The towns of Lunenburg, Leominster, Shirley, and Fitchburg are being raised to moderate risk. (Please note: this press release has been revised to reflect that Lunenberg is in Worcester County.) 

“With this evidence of an animal infected with West Nile virus, we know that there are the right conditions and enough disease circulating to result in a human infection,” said Public Health Commissioner Robbie Goldstein, MD, PhD. “The elevated temperatures combined with high humidity increase mosquito activity. We want to remind people that there are easy ways to prevent mosquitoes from biting you, like using mosquito repellent when you are outdoors and being mindful of peak mosquito activity hours.”

WNV is usually transmitted to susceptible animals and humans through the bite of an infected mosquito. The first evidence of WNV in mosquitoes in 2025 was announced on June 17, and 10 positive mosquito samples identified so far this year. There have been no human cases of WNV detected. There were nineteen human cases of WNV in 2024 and no animal cases. No evidence of Eastern Equine Encephalitis (EEE) has been found so far this season. There were four human cases of EEE and three animal cases – all in horses – 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.

“Animals that live outdoors are at somewhat higher risk from arboviruses than humans who spend more time indoors,” said State Epidemiologist Dr. Catherine M. Brown. “But the weather this summer is creating the opportunity for it to be a busy WNV season and it is important to take steps to prevent mosquito bites.”

People have an important role to play in protecting themselves and their loved ones from illnesses caused by mosquitoes.

Avoid Mosquito Bites

Apply Insect Repellent when Outdoors. Use a repellent with an EPA-registered ingredient (DEET (N,N-Diethyl-m-toluamide), permethrin, picaridin (KBR 3023), oil of lemon eucalyptus (p-menthane-3,8-diol (PMD) or IR3535) according to the instructions on the product label. DEET products should not be used on infants under two months of age and should be used in concentrations of 30 percent or less on older children. Oil of lemon eucalyptus should not be used on children under three years of age.

Be Aware of Peak Mosquito Hours. 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.

Clothing Can Help Reduce Mosquito Bites. Wearing long sleeves, long pants, and socks when outdoors will help keep mosquitoes away from your skin.

Mosquito-Proof Your Home

Drain Standing Water. Mosquitoes lay their eggs in standing water. Limit the number of places around your home for mosquitoes to breed by either draining or discarding items that hold water. Check rain gutters and drains. Empty any unused flowerpots and wading pools and change the water in birdbaths frequently.

Install or Repair Screens. Keep mosquitoes outside by having tightly fitting screens on all your windows and doors.

Protect Your Animals

Animal owners should reduce potential mosquito breeding sites on their property by eliminating standing water from containers such as buckets, tires, and wading pools – especially after heavy rains. Water troughs provide excellent mosquito breeding habitats and should be flushed out at least once a week during the summer months to reduce mosquitoes near paddock areas. Horse owners should keep horses in indoor stalls at night to reduce their risk of exposure to mosquitoes. Owners should also speak with their veterinarian about mosquito repellents approved for use in animals and vaccinations to prevent WNV and EEE. If an animal is suspected of having WNV or EEE, owners are required to report to the Department of Agricultural Resources, Division of Animal Health by calling 617-626-1795, and to the Department of Public Health by calling 617-983-6800.

More information, including all WNV and EEE positive results, can be found on the Arbovirus Surveillance Information web page which is updated daily, or by calling the DPH Division of Epidemiology at 617-983-6800. 

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