Mosquito in Harvard tests positive for eastern equine encephalitis

A mosquito in the west side of Harvard tested positive for eastern equine encephalitis (EEE) on Aug. 19, raising Harvard’s EEE risk level from low to moderate. The Harvard Board of Health (BOH) was informed immediately and posted warnings on social media site Nextdoor Harvard and the town website, advising residents to take precautions.

The Massachusetts Department of Public Health (MDPH) conducts tests statewide for mosquito-borne diseases each year and assigns one of five EEE risk levels to every town: remote, low, moderate, high, and critical. The moderate level is assigned to towns where EEE occurred in the past year or where there is EEE activity now. Two mosquitos in Bolton and two in Shirley also tested positive for EEE on Aug. 19, and the EEE risk level in those towns was also raised to moderate.

MDPH advises residents of towns with a moderate risk level to wear mosquito repellent when outdoors, especially between dusk and dawn, and to avoid areas with high mosquito activity, such as swamps. The agency considers 7:45 p.m. dusk this week, and dusk arrives 15 minutes earlier each week from September through most of October. The BOH is notifying organizations in town that routinely sponsor evening outdoor activities that participants should take precautions to avoid being bitten (see Protecting against EEE below). The board is also advising residents who have symptoms consistent with the flu (see Recognizing the symptoms) to contact their doctors and mention that EEE has been reported in Harvard.

MDPH estimates that EEE outbreaks typically occur in Massachusetts every 10 to 20 years and last for two to three years. The most recent outbreak occurred between 2010 and 2012, when nine people contracted the disease and four died. While MDPH says it is difficult to predict risk levels for EEE for any given year, high groundwater levels in fall and winter may increase the survival rates for the mosquitos that carry the disease, and high temperatures during the summer increase all mosquito populations.

About 300 mosquitoes in Massachusetts have tested positive for EEE so far this year, compared to only two in 2018. Most of the positive results were in Bristol, Norfolk, and Plymouth counties in southeastern Massachusetts, and the state has responded to the outbreak in that area with aerial spraying over towns where the risk level is high or critical.

BOH asks for more testing

When a town’s risk level is raised to moderate, MDPH policy is to perform additional trapping and testing “if resources allow.” At an Aug. 20 Board of Health meeting, Chair Tom Philippou said he had spoken with Matt Osborne, the MDPH employee who conducted the test. Philippou said he asked if more tests would be done, but Osborne said MDPH did not know whether Harvard was scheduled for additional sampling. Board members agreed that Philippou should contact MDPH to ask for more testing.

Currently there is only one test site in Harvard. Philippou said he asked Osborne if the site was at Oxbow National Wildlife Refuge, and while Osborne told him the location of the site is confidential, he did say it was off Still River Road.
According to the MDPH, EEE is found naturally in some bird species that live near fresh-water swamps. It is spread when mosquitoes bite EEE-infected birds, and humans contract the disease when they are bitten by an infected mosquito. The majority of EEE-infected mosquitoes in Massachusetts are found in or near habitats with freshwater swamps, mainly in the southeastern part of the state.

But the disease is spreading. In its 2019 Arbovirus Surveillance and Response Plan, MDPH stated, “As indicated by virus activity surveillance, the geographic area of risk for EEE has increased outside the historical areas of southeastern Massachusetts.” It cites unusual EEE activity detected not only in more northern Massachusetts towns, but in some locations in New Hampshire, Vermont, and Maine as well.

More information, including risk level maps and daily updates on where mosquitoes have tested positive for EEE and West Nile Virus is available on www.mass.gov/mosquito-borne-diseases. Information on EEE is available at www.mass.gov/service-details/eee-eastern-equine-encephalitis. Informational links are also available on the town website on the Board of Health Public Health Information pages, and the board will continue to post urgent alerts on the town website as needed.