Wednesday, July 21, 2010

Eastern Equine Encephalitis (EEE)



# 4741



Yesterday the local news carried word of the death of an adult female in Hillsborough County (ie. Tampa region), Florida from mosquito borne EEE (Eastern Equine Encephalitis).


EEE (Triple `E’) is an often serious, but exceedingly rare illness in humans.  It is one of more than 100 kinds of arbovirus (viruses transmitted by arthropods  e.g., Mosquitoes, sandflies, midges, or ticks).


According to the MMWR  (here), between 1999 and 2008 there were a median of seven (range: 3--21) EEE cases (not deaths) reported in the United States each year.


In addition to EEE, West Nile virus (WNV), La Crosse virus (LACV), and St. Louis encephalitis virus (SLEV) also circulate at low levels in the United States.



While of concern, to keep things in perspective, on average 58 people are struck and killed by lightning each year in the United States, and Bee stings account for an additional 40 deaths each year.


Which isn’t to minimize EEE or any of the other arboviruses, or to suggest that people not take precautions against mosquitoes, but is simply a reminder that a lot of the diseases we talk about in this column are pretty rare.


In recent weeks, Dengue has become a big story here in Florida, but once again, we’re talking a couple of dozen confirmed cases out of a population of 18 million.


The actual incidence of Dengue is probably much higher, but as with most viruses, many cases are sub-clinical or asymptomatic and are therefore never diagnosed.  


First, the story about the EEE fatality, then a bit of discussion about the way this rare virus makes its way into the human population.


First human EEE death confirmed in Hillsborough County

State's first encephalitis death in two years

Updated: Wednesday, 21 Jul 2010, 6:18 AM EDT staff report

TAMPA - Health officials in Hillsborough County have confirmed the first human death this year from Eastern Equine Encephalitis.


A woman living in the northern part of the county died July 1, the county health department said, and it is believed that she had other health issues as well.


This is the first human death from EEE in the state of Florida since 2008.


Four horses in the county have also tested positive for the disease in the last several weeks, according to the health department. Officials say finding the disease in animals means that the likelihood of humans becoming infected increases.


Hillsborough County Mosquito Control will be spraying pesticides over much of the county Wednesday morning.

(Continue . . . )


While the number of yearly cases is low, the distribution of EEE in the United States far ranging.




The natural host for the EEE virus are songbirds, which can become infected generally without suffering ill effect.  The virus is spread among these birds by the blood feeding of female mosquitoes (males don’t bite).


After an infected mosquito feeds on a bird, the bird becomes infected and the virus begins reproducing. After a few days, and for only a few days, the bird’s bloodstream contains enough virus to infect subsequent mosquitoes that feed on it.


Culiseta melanura, which means "curly black hairs", is the species of swamp mosquito that serves as the primary vector for this virus among birds.


It, however, isn’t usually attracted to bite humans.


So it generally requires a secondary type of mosquito - one that isn’t quite as picky a feeder - such as the Aedes albopictus or  Coquillettidia perturbans  `salt and pepper’ mosquito, to bite an infected bird in order to move it into the equine or human population.


Humans and horses don’t develop a high enough viral EEE titer in their bloodstream to pass on the virus if they are subsequently bitten by a mosquito, so they are considered a `dead-end host’.


For more on this fascinating topic, I’ve found an absolutely terrific multimedia presentation on arboviruses in Florida.


It is a narrated slide show, by Rebecca Shultz, the Arthropod-borne Disease Surveillance Coordinator for the Florida Department of Health, and it covers EEE, SLEV, and West Nile Virus.


The presentation runs just over 20 minutes.   The transcript is here.  Click the image below (or this link )to go to the slide show, and turn on your speakers.


Highly recommended.




As the Miami-Dade County Health Department reminds us, to protect yourself from mosquitoes, you should practice the “5 D's”:

  • Dusk and Dawn – avoid being outdoors when mosquitoes are very active 
  • Dress – wear clothing that covers most of your skin 
  • DEET – repellents containing up to 30 percent DEET (N, N-diethyl-meta-toluamide) are recommended. Other effective mosquito repellents include picaridin, oil of lemon eucalyptus, and IR 3535. Always read label directions for approved usage before your apply a repellent. Some repellents are not suitable for children. 
  • Drainage – check around your home to remove standing water, where mosquitoes may lay eggs.


As long as you observe these simple precautions (and this isn’t just advice for Floridians), you can reduce your (already slight) risk of being infected by any of these mosquito borne illnesses.


For those who would like to follow Florida’s surveillance program for arboviruses, weekly reports are available from the Florida Department of Health.


Weekly Data for Arbovirus Surveillance

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