West Nile virus and Eastern Equine Encephalitis: How to protect humans and horses alike

by Hillary on September 27, 2012

Horse and rider aerating a body of water to prevent mosquito larvae. Probably best to use a circulation pump, though.

This year has been a big year for West Nile virus (WNV) and Eastern Equine Encephalitis (EEE) infection, two mosquito-borne diseases that can cause severe neurological disease in humans and equines. For example, Massachusetts health officials recently confirmed its second human EEE death and seventh case this year. For comparison, the CDC states that there is an average of six cases of EEE a year in the United States. In regards to West Nile, The CDC reports that this year has seen the highest number of cases since 2003 and 147 reported deaths.

First, a little bit about the diseases – both are viral infections that can cause encephalitis (swelling in the brain). WNV can present with symptoms including, but not limited to, disorientation, high fever, and stiff neck in humans and hind limb weakness, hind limb paralysis, and fever in horses. Case fatality in horses is estimated to be 33%. EEE can also present with multiple symptoms. In humans, those can include fever, convulsions, and vomiting/diarrhea. In horses, the infection can present with fever and a lack of coordination.

Humans can avoid infection by reducing how frequently mosquitoes bite. This can be accomplished by removing mosquito breeding areas in the environment (be it home, yard, or barn) or by protecting yourself against bites. Since horses are frequently outside for turnout and barns are typically not sealed in such a way as to keep out mosquitoes, the best method to protect horses is to get them vaccinated yearly.


  • Fix screens in windows and doors.
  • Wear repellant and long sleeves/pants.
  • Avoid being outside when mosquitoes are active (dusk and dawn, primarily).
  • Remove sources of stagnant water (where mosquitoes breed). You can add circulators to bird baths or fountains to larger standing bodies of water. Make sure that any standing water in buckets, tires, ect gets dumped.
  • Vaccinate horses yearly for WNV and EEE. Check with your veterinarian to make sure all horses are up to date on vaccines.

Even if you take precautionary measures, it’s still possible to meet the wrong mosquito at the wrong time. If you or your horse gets sick, please call your physician/veterinarian!

Information sources:


Margaret Freaney September 27, 2012 at 11:02 am

Nice topic, I like that you put in what people should do to prevent WNV. The information in the first paragraph is a little confusing to me.

Are the cases of EEE only 7 cases for humans, or 7 cases for humans and horses? Is this only in Michigan, or are there more cases other places?

Also is the 147 cases of WNV for 2003 or for this year? If it is for 2003 how many cases were reported this year?

Your post seems to be a lot like the,” West Nile Cases Still Rising; Death Toll Now at 134, CDC Says.” that you link to in the first paragraph.

Is there a way to tell if you are coming down with a normal flu (which most people won’t go to the doctor for right away) vs. West Nile Virus or EEE?

What are the most important symptoms to watch out for?

I don’t really know that much about EEE, Is it called this because it mostly effects horses? If so when did human cases start up?

Again, I like your topic. I think this can be very interesting to people, especially those of us who camp or hike a lot. I don’t think I have managed a summer without at least 10 mosquito bite. (luckily none have caused any sickness)


Hillary September 27, 2012 at 4:07 pm

Hi Margaret,

Thanks for the feedback! Shara touched on some of what you brought up in the comments below. In regards to symptoms that would differentiate WNV and EEE from the flu, you would look for symptoms of neurological involvement and encephalitis (convulsions, stiff neck, disorientation, ect.). Check the CDC website for more information on what to look for in humans.

Margaret Freaney September 27, 2012 at 10:44 pm

Thank you, you and Shara cleared up a lot of my questions.


lara September 27, 2012 at 12:13 pm

Wow, I didn’t even realise they had those vaccinations available for my horses. Thank you, we’ll definitely take better care of ourselves this season!

Hillary September 27, 2012 at 4:04 pm

Hi Lara,
Thanks for commenting! That’s great that the information was helpful to you! Please pass the knowledge on to other horse owners.

Shara E September 27, 2012 at 1:26 pm

I think the cases are referring to the 7th EEE case in Humans and the 2nd EEE fatality in Massachusetts. Not sure what the country-wide stats are, since i had no luck finding data after 2010.

I hate mosquitoes. You’ve given me even more reasons to hate them. Yay! I agree that the format of your post is similar to the article Margaret mentioned, but i think it gives some new info, particularly not just on human care, but also equine. I’d love to hear more about how it wound up in humans as well!

Yay you!

Hillary September 27, 2012 at 4:11 pm

Thanks! :-)
To answer both Shara and Margaret, I had difficulty finding good information (i.e. not wikipedia) on when EEE was first diagnosed in humans and horses respectively. As the name would suggest, it was first isolated in horses. Humans are more than likely “spillover hosts” of the disease. That means that the disease established itself in an equine/mosquito transmission system, and then due to population changes (larger human populations living near horses, for example) was able to infect more human hosts.

Liz September 27, 2012 at 1:43 pm

Hi Hillary,
I love the fact that you kept the article concise, and the joke in the caption. Overall, I think it might have suffered a bit because it was so short. It really felt like I was reading a bunch of numbers, and there wasn’t really space to digest them. Some interpretation or opinion might have been nice after the statistic. I would love a little more personality! Maybe tell us why you’re interested in this subject? Great job though!

Hillary September 27, 2012 at 4:02 pm

Hi Liz,
Thanks for the feedback! I was trying to balance information with brevity (I get really geeky about infectious diseases, and I didn’t want to bore anyone!). I’ll keep that in mind next time.

Elizabeth Fryer October 1, 2012 at 8:18 pm

Hi Hillary,
Andrew Maynard let his LinkedIn connections know that students have started keeping health blogs and has asked for comments, saying that what you all desire most of all are “critical comments that help them improve.” I am a science editor and had horses growing up. (The Website I provided is to my book website. I was in a coma for 3 weeks as a result of a horseback riding accident. I wrote a book about my recovery.)

The first link you give for “big year.” Consider extending the text for that link to include “for West Nile virus (WNV) and Eastern Equine Encephalitis (EEE) infection.” Sure, it’s long, but it’s more descriptive for the link.

That link took me CDC’s site but I couldn’t get back to your blog post. Generally, you don’t want to direct readers away from your site. In this instance, with the supplemental info, you don’t want to include that in your short post, but have the link open a new window—or at least make sure the “back” button works from the linked-to site.

Regarding your reply to Margaret’s comment, where you say “Check the CDC website for more information on what to look for in humans”: A top rule in professional writing is Don’t make your reader have to work to get the meaning of your writing. If the website gives too much info for you to list, at least provide the link to where that info is. Even if it’s the same link from your article above, don’t make Margaret have to scroll up to that link, wondering if that’s the link you mean in the first place.

The difference between flu and EEE symptoms might make a follow-up post??? I look forward to reading more of your writing.

holtight October 3, 2012 at 1:05 pm

The info re WNV is pretty scary stuff given the scientific and observational indications of long-term climate change pointing to abnormal increases in temperature in many areas. Stay informed; stay healthy!

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