Mass. health officials warn of mosquito-borne EEE and West Nile virus

Health officials in Massachusetts are urging caution about mosquito-borne illnesses after this year's first human case of West Nile virus and first animal case of Eastern equine encephalitis, or EEE.

The Department of Public Health said Tuesday that a man in his 40s was exposed to West Nile virus in Hampden County. A horse was diagnosed with EEE, which officials said the animal contracted in Plymouth.

Both viruses were detected in mosquitoes earlier this summer.

West Nile virus usually causes fever and flu-like symptoms, but in rare cases can cause severe illness. There were six human cases in Massachusetts last year.

EEE is rare, but poses a serious threat to infected people of all ages.

The last known human case of EEE in Massachusetts occurred in 2020, when five people were infected and one died. A year earlier, in 2019, there were six deaths among 12 human cases in the Bay State.

There were six human cases of West Nile in Massachusetts last year.

The DPH noted that August and September are months of particular concern for mosquito-borne illnesses in Massachusetts.

"We continue to recommend taking steps to prevent mosquito bites until the first hard frost," Dr. Catherine Brown, the state epidemiologist, said in a statement shared by the department. "People should use mosquito repellent with an EPA-registered active ingredient, clothing to reduce exposed skin, and consider rescheduling outdoor activities that occur during the evening or early morning."

Massachusetts Department of Public Health

Plymouth, where the horse was infected with EEE, is the third Massachusetts community to be categorized as high risk for that virus this year, joining Carver and Middleborough. The state lists 12 as having moderate EEE risk, including Amesbury, Groveland, Halifax, Haverhill, Kingston, Merrimac, Newburyport, Plymouth, Plympton, Salisbury, Wareham and West Newbury.

The state also noted that mosquito samples in Dedham have tested positive for EEE, and that town is now considered a low risk.

Massachusetts Department of Public Health

There are moderate risks of West Nile virus in parts of Suffolk County, Middlesex County, Norfolk County, Bristol County, Essex County, Plymouth County, Worcester County and Hampden County.

Officials expect the mosquito population to increase throughout the summer and recommend, among other prevention techniques, avoiding outdoor activities in dawn and dusk, when mosquitoes are most active.

The Department of Public Health says people can call its Division of Epidemiology at 617-983-6800 for more information about the mosquito-borne illnesses.