When the dog days end, it’s Triple E time.

By Chris Williams on July 14, 2012.


The end of the ‘dog days’ of summer in the first half of August seem to coincide rather nicely with the first reporting of Triple E positive mosquitoes. (This is not a good thing!)  The past few years this trend seems to be right on schedule. (

So what exactly is Triple E? (EEE) It’s just an easier way of saying Eastern Equine Encephalitis, which is a mosquito-borne viral disease (fortunately rare) responsible for severe and often fatal encephalitis (inflammation of the brain) in humans and horses. New Hampshire reported two fatalities from Triple E in 2009, while Massachusetts reported a single fatal case in 2011. The causal agent was first identified during the late 1930’s, and since that time, several outbreaks of EEE virus affecting horses and humans have been recorded both in Massachusetts and New Hampshire.  In 1999, an outbreak of a related virus in New York City (later identified as West Nile Virus) resulted in 7 human fatalities.  Since the early 2000’s, WNV has been isolated from migratory birds (principally the American crow) and found in certain mosquito populations throughout New England.  The two viruses EEE and WNV are most likely maintained entirely in bird populations with exclusive bird feeding mosquitoes (Culiseta sp.).  However, they (EEE, WNV) can easily be transmitted to horses and humans by mosquitoes that feed upon both birds and mammals such as Coquillettidia perturbans, which is the principal ‘bridge’ vector between birds and mammals for EEE (A. Eaton, 2006). Certain other species of mosquito with this dual feeding habit (several Culex sp, and Ochlerotatus sp.) may be involved as well.


What should be the take-away from this short EEE/WNV history lesson and its’ etiological tree? Be aware of the risks, and take precautions to prevent being bitten like limiting outdoor activities near dawn or dusk when mosquitoes are most active. (Mosquito populations around my yard last September were insanely high due to a very wet August making outdoor chores after work nearly impossible without protection.)  Wear protective clothing, insect repellants, and keep them out of sleeping quarters with properly screened doors and windows.  Another strategy for property owners to help reduce risk of exposure to encephalitis viruses is to stop breeding mosquitoes!  Although the principal Triple E vector mosquito (C. perturbans) breeds in wetlands, the ones responsible for transmitting West Nile virus (Culex pipiens, C. restuans, and others) will breed in any object around the yard that can hold water such as buckets, wheelbarrows, birdbaths, old tires and clogged gutters. Proper storage and regular maintenance of these items will go a long way towards reducing your exposure risk.

For more information, please visit the following links.



We’re not satisfied until you are. Learn More