Aerial pesticide spraying reduced mosquitoes in southeastern Massachusetts, but EEE risk remains

Aerial spraying of pesticides across 21 communities in Southeastern Massachusetts slashed mosquito populations by about 60 percent, state public health officials announced Monday, but they cautioned that the remaining insects can still spread Eastern equine encephalitis.

Planes took to the skies July 20 -22 after several pools of mosquitoes infected with EEE were found in the region, and specialists determined the insects were the type that typically bite people.

Eastern equine is an often fatal mosquito-borne illness that can affect people of all ages.

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Here is the latest from state officials:

Aerial spraying generally only kills mosquitoes in flight during the spray operation, and the risk of eastern equine encephalitis (EEE) remains a concern with the identification of multiple pools of EEE-positive mosquitoes within portions of the spray zone.

“Following aerial spraying, we have seen a significant reduction in the volume of mosquitoes,” said Public Health Commissioner John Auerbach. “But as we have seen after past sprays, the public must be mindful that the risk of EEE remains persistent. People are advised to take precautions, including the use of mosquito repellant and avoiding outdoor activities between dusk and dawn, when mosquitoes are most active.”

Aerial spraying took place across 21 communities in Southeastern Massachusetts during the evenings of Friday, July 20, Saturday, July 21 and Sunday, July 22.

Seven communities are currently at a high risk level for EEE: Canton, Easton, Lakeville, Raynham, Rehoboth, Taunton and West Bridgewater. Communities deemed “high risk” are advised to curtail evening activities for the remainder of the season. A map of communities and their risk levels can be found at

Since the spraying operation concluded, EEE-positive mosquito pools have been found in Easton and Hanson. Local mosquito control projects continue to conduct ground spraying throughout the area, and trapping and monitoring have been enhanced to monitor the on-going EEE risk.

There have been no human cases of West Nile virus (WNV) or EEE so far this year. There were two cases of EEE in August of last year acquired in Massachusetts; a fatal case in a Bristol County man and an infection in a tourist from out of state. EEE activity in both 2010 and 2011 raised public concern and prompted DPH to work with a panel of experts to evaluate and enhance the state’s surveillance and response program. EEE is spread to humans through the bite of an infected mosquito. EEE is a serious disease in all ages and can even cause death.

People have an important role to play in protecting themselves and their loved ones from illnesses caused by mosquitoes.

Avoid Mosquito Bites

•Apply Insect Repellent when Outdoors. Use a repellent with DEET (N, N-diethyl-m-toluamide), permethrin, picaridin (KBR 3023), oil of lemon eucalyptus [p-methane 3, 8-diol (PMD)] or IR3535 according to the instructions on the product label. DEET products should not be used on infants under two months of age and should be used in concentrations of 30% or less on older children. Oil of lemon eucalyptus should not be used on children under three years of age.

•Be Aware of Peak Mosquito Hours. The hours from dusk to dawn are peak biting times for many mosquitoes. Consider rescheduling outdoor activities that occur during evening or early morning.

•Clothing Can Help Reduce Mosquito Bites. Wearing long-sleeves, long pants and socks when outdoors will help keep mosquitoes away from your skin.

Mosquito-Proof Your Home

•Drain Standing Water. Mosquitoes lay their eggs in standing water. Limit the number of places around your home for mosquitoes to breed by either draining or discarding items that hold water. Check rain gutters and drains. Empty any unused flowerpots and wading pools, and change water in birdbaths frequently.

•Install or Repair Screens. Keep mosquitoes outside by having tightly-fitting screens on all of your windows and doors.

Protect Your Animals

Animal owners should reduce potential mosquito breeding sites on their property by eliminating standing water from containers such as buckets, tires, and wading pools — especially after heavy rains. Water troughs provide excellent mosquito breeding habitats and should be flushed out at least once a week during the summer months to reduce mosquitoes near paddock areas. Horse owners should keep horses in indoor stalls at night to reduce their risk of exposure to mosquitoes. If an animal is diagnosed with WNV or EEE, owners are required to report to DAR, Division of Animal Health by calling 617-626-1795 and to the Department of Public Health (DPH) by calling 617-983-6800.

More information, including all WNV and EEE positive results from 2012, can be found on the Arbovirus Surveillance Information web page at or by calling the DPH Epidemiology Program at 617-983-6800. The findings of the DPH Eastern Equine Encephalitis Expert Panel can be found here: