Two Health Districts take Two Different Approaches to Prevention of EEE Across Eastern Connecticut


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After last year’s record-breaking number of Eastern Equine Encephalitis cases, the state and local health districts are beginning to step up their mosquito control efforts through expanded testing and distribution of larvicide.

Both the Connecticut River Area Health District (CRAHD) and Ledge Light Health District are distributing larvicide in an effort to reduce the mosquito population, however they are taking markedly different approaches.

In June, CRAHD began treating storm drains in Deep River, Chester, Old Saybrook, Haddam and Clinton with biological larvicide that directly targets biting flies, like mosquitos, and does not impact the drinking water supply.

“Knowing how important it is to reduce the adult mosquitoes to reduce the incidence of transmission the CT River Area Health District has hired a contractor to treat all the storm drains,” director Scott Martinson wrote in an email to the five area towns. “Although these measures do not eliminate every mosquito it does help to control the adult population which therefore reduces risk.”

Ledge Light Health District, by contrast, has decided against widespread use of larvicides. Instead, the regional health district is offering individual mosquito control consultations and larvicide treatment to private residents in East Lyme, Groton, Ledyard, Old Lyme, New London, North Stonington, Stonington and Waterford.

The consultations and treatments are free to all residents in the eight towns.

According to Philip Armstrong, a virologist and medical entomologist at the Connecticut Agricultural Experiment Station, neither of these types of treatments are necessarily helpful in preventing Eastern Equine Encephalitis, or EEE.

“These treatments get rid of common backyard mosquitoes,” he said. “EEE is very hard to treat with larvicide because the mosquitos that carry it grow in swamp trees and are very hard to reach.”

Consistent application, the approach taken by CRAHD, does help to prevent the spread of West Nile Virus and can help prevent EEE transmission if the virus overflows into the common mosquito population, as can happen in large outbreak years. However, intermittent, nuisance treatments, like those offered by Ledge Light, would not have the same impact, said Armstrong.

On a statewide basis, the Department of Energy and Environmental Protection does not normally employ large scale larvicide treatments and nearly always leaves insecticide applications up to individual towns and health districts.

“The state has only been involved once in insecticide spraying,” Armstrong said. “It is only done very rarely and usually only if there are human cases that come to light early enough in the season so that we can go in and spray and have an impact.”

Even last year, with four human cases, the state did not engage in county-wide insecticide application.  

“It’s a consequential decision when spraying the whole county,” Armstrong said. “It has to be mounted very early, like August, in order to make a difference.”

And that’s why expanded testing of the mosquito population for EEE during the 2020 season could be important.

Despite an early end to the legislative session, the Connecticut Agricultural Experiment Station managed to secure $100,000 in funding from the state finance advisory committee in addition to $50,000 from the station’s surplus to add new traps in eastern Connecticut specifically designated for monitoring for EEE. The Experiment Station now operates 108 traps statewide and hopes to detect EEE as early as possible so the public can be made aware and spraying can commence if necessary.

“Typically, the earliest we would detect EEE in Connecticut is late July or early August, but Massachusetts already detected Triple E at one site in Franklin County,” Armstrong said. “It’s hard to know what to make of that. It is somewhat noteworthy that they did detect it so early, but we don’t know what it will mean for Connecticut and how bad this season could be.”

For now, as Armstrong said, it’s a waiting game: will there be a resurgence of EEE, will it result in any human cases and if so, will the larvicide that CRAHD has applied help reduce the spread.