Massachusetts and New Hampshire Confirm Additional Eastern equine encephalitis and West Nile virus Cases

In the northeastern section of the United States, concerns about the impact of Eastern equine encephalitis (EEE) and West Nile virus (WNV) have continued into September 2024.

The Massachusetts Department of Public Health (DPH) announced on September 5, 2024, one additional human case of EEE and one additional human case of WNV in Massachusetts this year.

The total number of EEE cases in Massachusetts this year is three, with seven WNV cases.

WNV risk levels in the following communities are being raised to high: Stoneham and Wakefield in Middlesex County.

Throughout the U.S., 38 states have reported WNV cases in 2024.

The last outbreak of EEE occurred in 2019-2020 and resulted in 17 human cases and seven deaths. In 2023, there were six human cases of WNV.

As of September, EEE risk levels have been raised to high in Acton, Ayer, Boxborough, Carlisle, Littleton in Middlesex County, and Harvard in Worcester County. The following communities are being raised to moderate: Bedford, Billerica, Chelmsford, Concord, Framingham, Groton, Lincoln, Shirley, Stow, Tyngsborough, Wayland, and Westford in Middlesex County; and Berlin, Bolton, Clinton, and Lancaster in Worcester County.

Public Health Commissioner Robbie Goldstein, MD, PhD., commented in a press release, “It is essential that residents continue to use mosquito repellent with an EPA-registered active ingredient every time they are outdoors. We also strongly recommend that residents and towns in high-risk areas for EEE reschedule their evening outdoor events to avoid peak mosquito biting hours.”

EEE and WNV are transmitted to humans through the bite of an infected mosquito.

“Mosquito behavior starts to change in September,” said State Epidemiologist Dr. Catherine Brown. “They will be less active during cooler temperatures. However, during warmer weather, such as being forecast for the end of next week, mosquitoes will be out and looking for their next meal.”

To the north of Massachusetts, the New Hampshire Department of Health and Human Services reported on September 4, 2024, that ten mosquito batches tested positive for EEE this year, with one fatal human case.

The last reported human cases of EEE in New Hampshire were in 2014 when three cases were identified. Two of those patients died.

As of September 6, 2024, no vaccines are available for people to protect themselves against EEE or WNV.