A mosquito collected in Worcester has tested positive for West Nile virus, the rare and potentially dangerous mosquito-borne illness that has plagued Massachusetts for decades.
Worcester announced it would begin spraying insecticide around a neighborhood near Lake Quinsigamond. The truck-mounted sprayers hit the streets Thursday.
City officials urged residents to keep themselves and their pets indoors until about 20 minutes after spraying. Windows should remain closed, and any home garden vegetables should be thoroughly washed after treatment is deployed.
First identified in the U.S. in 1999, West Nile is often symptomless, but in about a fifth of cases patients experience rashes, fever, headaches and other mild ailments. Less than 1% of patients experience severe complications like encephalitis (swelling in the brain) and meningitis (swelling of the membrane around the brain or spine), according to the Massachusetts Department of Public Health.
Because West Nile so often passes without symptoms, it’s rarely reported in Massachusetts. There were 273 cases reported between 2001 and 2025, according to the state.
The best way to avoid West Nile is to limit mosquitoes’ chances of biting you. Public heath experts recommend wearing long sleeves and pants at dusk and dawn, when mosquitoes are most active. They also implored people to drain standing water on their properties and to use DEET-based bug repellents.
Editor’s note: Shortly after publication, Worcester clarified that the West Nile detected came from a mosquito sample, not a person.
