Barnyard Week: Of horses and herpes

This post isnt going to be as funny or as ripe for Pope jokes as some of you might be hoping. Sry.

Herpes in horses EHV, has a lot of similarities to the ‘herpes’ us humans are used to– HSV-1 and 2, EBV, CMV, chicken pox, etc. Its similar in that, I mean, its herpes. Large, DNA virus. Once it sets up shop in someone, its going to be there for life. And, usually most horses are infected with EHV variants while they are still very young, from Mom. Like EBV and CMV and Co, its pretty ubiquitous. Horses/Colts get sick (like how you feel when you get the flu) and get better, no big whoop. And of course, it can reactivate when the horse is stressed out.

Unfortunately its also similar to herpes viruses in a scary way– Sure, lots of horses are infected with EHV variants, and normally its not a big deal. But, a specific, random mutant of EHV-1 kills horses/colts in a similar way HSV can kill humans– encephalitis. Of the horses that are infected with EHV-1, it looks like 10-15% of them could develop a neurological form of the disease. Even if they dont, EHV-1 is a big deal for infected preggers Mama horseys, just like HSV-2 is for preggers Mama humans– while humans might still give birth and the baby will die shortly after from encephalitis, usually in horses the colt will spontaneously abort.

Which brings me to the scary difference between ‘human’ herpes and ‘horse’ herpes– EHV is apparently extraordinarily contagious. Its not like its spread by horses boinking or making out– EHV is spread by aerosols (simply snorting), and horses can even catch it just hanging out in a place an infected horse was previously hanging out, or via handlers clothing or using grooming supplies on multiple horses.

Why do I bring this up now? There is currently an outbreak of EHV-1 in the US, stemming from a competition in Utah a few weeks ago. Horses traveled to the competition, interacted with or were exposed to a sick horse, got infected, and carried the virus back home to their ranches and all the horses there.

There is a ‘vaccine’ for EHV, but apparently while it can help prevent the cold-like symptoms or the abortions EHV-1 can cause, it doesnt do much to prevent the neurologic disease. Since a pretty large percentage of EHV-1 infected horses can develop the neurologic form, this outbreak could mean there is a risk of having a whole bunch of sick/dead horses in a couple of weeks. Thankfully, it appears only a few horses have died so far, and it doesnt look like any of the horses exposed to the exposed horses are getting sick. When word got out that EHV-1 was at that event in Utah, owners quickly did the right thing: quarantining the horses that might be sick, thus stopping a potential epidemic in its tracks.

Alas, this also means that a lot of horse events– not just competitions, but even parades, are being canceled because everyone is keeping their horses at home. Better to miss out on a Memorial Day parade than run the risk of losing your horsies. And the places that are having events with horses are making sure they abide by some pretty strict protocols to try to keep all the horses safe– like keeping them far apart from one another before/during/after events.

So this Memorial Day weekend, if you happen to notice that the horses in your local parade are spaced out a little weird, by themselves in a line rather than several horses walking abreast, well, now you know why.


  1. #1 Poodle Stomper
    May 25, 2011

    How does it affect humans? I know that in our primate facility everyone needs to be trained on the effects of HerpesB simply because it is 80% lethal (although granted, primates are more closely related to us than horses).

  2. #2 biopunk
    May 25, 2011

    The Equine herpesvirus 1 vaccine provides approximately a 4 month protective immunity.

    Not being up on horses, this seems quite low to me.

    Can any vets/horse owners tell me if there are any other vaccinations that are as short or as frequent as EHV-1?

  3. #3 supratall
    May 26, 2011

    OK, I’ll come clean: this reminds me of an embarrassingly recent conversation with my materials science-trained boyfriend.

  4. #4 Birger Johansson
    May 26, 2011

    Since this is a DNA virus, would it be possible to make a vaccine made of a “mutilated” version, using DNA analog “words” that code for the same RNA as the original virus but with less efficiency? I seem to recall there are fewer RNA “words” than DNA, with several cases of different DNA coding for the same RNA.
    The body would get the same immune response but the virus would be too sluggish to pose a threat.

  5. #5 Mary
    May 26, 2011

    I failed my maternity rotation because of HSV….. I (and anyone with symptoms) was banned from the nursery….

    nearly failed it the 2nd time around cuz I was so stressed about the 1st fail…I broke out again… sigh

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