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Equine Herpes Virus
EHV-1
stands for “Equine Herpes Virus-1.” It’s given the “1″ because there are
several herpes viruses that affect horses and this one was named first. Otherwise, the “1” has no significance. Herpes viruses are very successful viruses,
if you measure success in terms of how many of them there are, and how many
mammalian species are affected. There are herpes viruses of horses, and
people, and dogs, and cats, and pigs, and cattle, probably several other
animals as well. Herpes viruses are
successful for two main reasons:
1)They
usually don’t hurt the host very much. That’s right, most of the time,
herpes viruses are unnoticed by the host. It doesn’t do a virus much good
to go killing off its host – that’s one reason why you don’t see Ebola virus
spreading rapidly around the world. If the host doesn’t live, the virus
can’t spread. Mostly, herpes viruses don’t cause much fuss. They
are sort of like the quiet family that lives in the dark house down the street,
or in the apartment down the hall. If you didn’t know that they were
there, you wouldn’t know that they were there.
2)They
have cleverly figured out how to evade the body’s immune system. Once a
horse gets infected with a herpes virus, the virus finds a nice home, usually
in and around nerves. There, they stay nice and quiet (medical folk say
latent), until some stress causes the virus to activate and start causing
trouble. And the fact that they can evade the body’s immune system also
means that, so far, nobody has been able to develop an really effective vaccine
against them.
Do you
get cold sores? Something like 70% of the human population does.
Most of the time, people with cold sores have perfectly normal looking
lips. But add some stress – say, illness, tax returns, school (for kids)
– and, BOOM, you end up with a big, painful knot on your lip. Then, the
body fights it off, and the virus goes latent, waiting for another stressful
opportunity.
In
horses, depending on the study you read, it’s estimated that as many as 50% (or
more) carry the latent EHV-1 virus in some form. Sending 700-some horses
to Ogden, Utah to compete in a horse show was the equine equivalent of sending
the kids to school. Panicked, excited, stressed, and packed together, it
was an absolutely perfect scenario for the herpes viruses to come out and
play. So, some poor horse – one of hundreds that were probably carrying
the virus – stressed, and far away from home, broke with the virus, which
reproduced, and then spread to other horses. Think kids in school with a
cold: one of them gets sick, and before you know it, everyone gets sick.
Remember
when I said that herpes viruses usually don’t hurt the host very much?
Well, that’s usually true. Unfortunately, in some cases, the EHV-1 virus
gets into the horse’s nervous system and causes a great deal of mischief.
It can even cause horses to die. This is unfortunate, and also not
uncommon with viruses. And, we do not
completely understand why some horses will develop the neurologic form and other
horses do not. Researchers believe that
the variety or strain of virus, the horse’s own immune system and the
environment all play a role in determining which horses will develop the
neurologic form. The good news is most horses that get exposed to the EHV-1 virus DON’T
get neurologic disease.
Of
course, no one wants any horse to get sick, ever, so, understanding that, your
reasonable question would be, “What can/should we do?”
And my
response would be, “Go out and enjoy your horse. The EHV-1 virus is pretty much
everywhere. Your horse has probably already been exposed
at some point in his life.
A big
question exists concerning vaccination for herpes virus. Unfortunately, there’s no really good herpes
virus vaccination that completely prevents any form of the disease caused by
herpes virus. This isn’t just a horse
thing; there’s no really good herpes virus vaccination against any disease of any species. (And, that is another reason why herpes
viruses are so successful). With that
said, there are several, commercially-available vaccines that we use routinely
in horses. These vaccines are labeled
(approved by the FDA) to prevent infection or reduce disease of the respiratory
and abortion strains. No vaccine prevents the neurologic form of
herpesvirus. Vaccinating against
herpes virus might help to decrease the shedding of the virus and the spreading
of the virus among horses. The best
advice is to consult your veterinarian concerning vaccination---not only when
discussing herpesvirus but to develop an entire vaccination program that best
works for you and your horse.
The
best things that you can do to avoid herpes virus is to practice good hygiene
measures, that is, the types of things that people should do with their horses
anyway (but often don’t).
For
example, new arrivals to farms should be quarantined for a few weeks before
being introduced to new horses. People working around horses should wash
their hands often so that they don’t carry disease. If
you’re working around a sick horse, change your clothes before moving on to the
next horse. Don’t crowd horses together. Feed them well. Get
them fresh air and exercise. All common sense and but important, too.
Bottom
line is EHV-1 can be a bad deal for individual horses. Quarantining sick
horses, or horses that were exposed at the show in Utah was absolutely the
right thing to do. But for most horses, EHV-1 will not cause disease.
So, be prudent and be cautious. Use good
hygiene measures. And discuss with your
veterinarian the risks and benefits of vaccination.
A special thanks to Dr. David Ramey in Sunland, CA for letting me "steal" his information about EHV-1. Check out his website for more great equine information @ www.doctorramey.com
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