EEE, West Nile: Local Risk Of Mosquito Disease Rises, Experts Urge Caution

MILFORD, MA — Mosquito season took a serious turn on Friday when the state confirmed the first human case of Eastern equine encephalitis in Massachusetts in Worcester County, prompting health officials to urge residents to take serious precautions, especially while outdoors.

As of Monday, Sutton, Oxford, Webster and Douglas were all at the "critical" EEE risk level, while surrounding communities including Upton, Grafton, Millbury, Millville, Uxbridge, Northbridge, Auburn, Leicester, Southbridge, Charlton and Dudley were all either "high" or "moderate" EEE risk.

Meanwhile, Worcester, Grafton and Shrewsbury were all at "moderate" West Nile risk, the only three communities in the county at that high of a level. Two people — a Hampden County resident in his 40s and a Middlesex County resident in his 70s — had contracted the potentially serious virus this summer so far.

The Worcester County EEE case is the first in a human since 2020, when five residents contracted the disease and one person died. The worst year for EEE was in 2019, when 12 people were infected and six died during the late summer and fall months.

Mosquitoes transmit EEE by biting birds that are a natural reservoir for the virus, although birds don't typically develop serious disease from EEE. Some experts theorize that the types of mosquitoes that carry the disease begin biting humans toward the end of summer as preferred bird populations begin to migrate out of the area. The types of mosquitoes that carry EEE are also typically found in swampy areas.

At this point in the season, state health officials are now recommending residents in higher-risk areas postpone events that take place at either dawn or dusk — times when mosquitoes are most active. In past EEE years, these precautions have led school districts to postpone or reschedule sporting events that typically take place in the evening hours.

"In addition to recommending that people use mosquito repellent with an EPA-registered active ingredient and clothing to reduce exposed skin, we also recommend that evening outdoor events be rescheduled to avoid the hours between dusk and dawn. The mosquitoes most likely to spread EEE are most active during the dusk to dawn hours," State Epidemiologist Dr. Catherine Brown said in a news release Friday.

Apart from avoiding high-risk parts of the day, here's what health officials are advising:

• Use repellents that contain DEET, picaridin, oil of lemon eucalyptus or IR3535. Permethrin is also recommended, but can only be applied to pre-treat clothing and gear like tents and hiking boots. Permethrin cannot be applied directly to skin, and cannot be applied to clothing that's already being worn.
• Wear long sleeves and pants whenever possible
• Inspect window screens, and make repairs to prevent mosquitoes from getting into your home
• Drain standing water that mosquitoes can use to breed

Local residents can stay up to date on EEE and West Nile activity by viewing the state risk maps that are updated regularly. You can also find out when mosquito spraying will take place in Worcester County on the Central MA Mosquito Control Project website.