EEE Transmission Cycle
March 13, 2010

After an unusually busy week, today’s thoughts are on the EEE Transmission Cycle. Here’s my first question to you: Where does EEE originate? There’s been much misinformation given as to where EEE begins its life cycle. This is partly because its name-Eastern Equine Encephalitis-describes the disease as being of “Equine” or horses. Another major reason is because there is confusion between the two main players or “vectors” in the transmission cycle of EEE.

According to Dr. Alan T. Eaton (UNH), EEE is “a mosquito spread disease of birds, that sometimes is transmitted (via mosquito bite) to horses and people.” In other words, birds contain EEE and are bitten by mosquitoes who then bite horses or humans to pass the EEE along. So in technical speak, it’s the primary/host vector (birds) to bridge vector (mosquito) to dead end host (humans or horses etc). Horses and humans are referred to as dead end hosts because when an infected horse or human is bitten by a mosquito there is no chance of EEE being passed on in reverse. The reason for this is because the concentration of EEE in a horse or human is far less than in a smaller animal such as a bird.

However, it must be made known that not every specie of mosquito carries or transmits EEE. There are some mosquitoes that only bite birds and which sustain the circle of the EEE disease life (primary vector to bridge vector to primary vector etc etc). Furthermore, there are those mosquitoes that bite both birds and humans and are the ones we are most concerned about. In all, according to Eaton, there are about 47 species of mosquitoes that live right here in NH, some transmit EEE and some don’t.

As we know, EEE is a deadly virus, and symptoms can range from mild flu-like to inflammation of the brain, coma, or death. And most who acquire the disease have lingering neurological effects. This is a serious disease and should be treated as such.

Next time we’ll have a look at the geography of the disease (my specialty) and how it can be used to create a system of knowing when EEE and its vectors are present.

Reference

Eastern Equine Encephalitis Could Return to New Hampshire this Summer                                                                                  Alan T. Eaton, PhD, UNH Cooperative Extension Entomology Specialist

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