Massachusetts Turns To Pesticide To Address Mosquito-Borne Threat

The Department of Public Health is moving on multiple fronts to address the elevated risks of mosquito-borne illnesses this year, including spraying pesticides from trucks in southern Worcester County and from planes in Plymouth County starting this week.

The truck-mounted and aerial spraying is meant to address the potential risks of the rare but serious Eastern Equine Encephalitis (EEE) virus, which spreads from the bites of infected mosquitoes and can be fatal. There were 17 human cases of EEE and seven related deaths during the state’s last EEE outbreak, in 2019-2020.

DPH announced has announced one human case of EEE so far this year, a male in his 80s who was exposed in Worcester County, and there are 10 communities considered to be at high or critical risk for EEE activity.

The spraying will take place at night, starting shortly after dusk and ending in the early morning. DPH said more details would be available on its website. The aerial spraying zone includes Carver, Halifax, Kingston, Middleborough, Plymouth, Plympton, Rochester, and Wareham, and the truck-mounted spraying zone covers Douglas, Dudley, Oxford, Sutton, and Uxbridge.

“Due to the increased EEE risk and the first human case of the season, the state is taking decisive action to protect public health,” Department of Agricultural Resources Commissioner Ashley Randle, whose department partners with DPH on spraying operations, said. “Aerial spraying will target mosquitoes carrying the EEE virus. While these measures are crucial for reducing transmission risk, it’s vital for everyone to stay vigilant and follow personal protection guidelines to safeguard our community.”

The state uses the EPA-registered pesticide Anvil 10+10 for mosquito spraying, applying it using an ultra-low volume aerosol that DPH said uses very small quantities of the chemical. DPH said people with known sensitivities or respiratory conditions like asthma should stay indoors during the spraying, though “it is unlikely a person would be exposed to amounts that would cause adverse health effects.”

It is considered safe to eat food grown in areas where Anvil 10+10 is sprayed, and animals do not necessarily need to be brought indoors, DPH said. But anyone who owns a small ornamental fishpond in the aerial spray area should cover it during the night of spraying and beekeepers are encouraged to consider applying a cover to hive exits to prevent bees from direct contact during spraying.

The packaging of Anvil 10+10 has been associated with harmful per-and polyfluoroalkyl substances (PFAS), a class of man-made chemicals that do not break down entirely in the environment, and exposure to their long-lasting presence has been linked to serious and negative health impacts. PFAS was found to leach from packaging into Anvil 10+10, creating thorny problems for some communities.

DPH is also cautioning residents to protect themselves against West Nile virus, which poses a threat especially to people older than 60, people who have received an organ donation, and those with conditions including cancer, diabetes, hypertension and kidney disease. The state said eight communities — Boston in Suffolk County; and Abington, Brockton, East Bridgewater, Marion, Mattapoisett, Rochester and Whitman in Plymouth County — are now considered to be at high risk for WNV.

“The risk from WNV is pretty widespread this year,” said State Epidemiologist Dr. Catherine Brown said. “In addition to recommending that people use mosquito repellent with an EPA-registered active ingredient and clothing to reduce exposed skin, check your window screens to be sure they don’t have holes and empty any containers that accumulate water around your yard.”

The first WNV-positive mosquito samples were announced July 2 and came from Quincy.  A total of 262 WNV-positive mosquito samples have been detected so far this year in almost every county (all except Franklin, Hampshire and Nantucket counties). The risk of human infection with WNV is moderate in Bristol County, Norfolk County, and the remainder of Plymouth County that hasn’t been moved into the high risk category, as well as in parts of Barnstable, Berkshire, Essex, Hampden, Middlesex, Plymouth, and Worcester counties, DPH said.