EHV-1/EHV-4, EHM, and Your Horse

5/16/2011

The social media sites and blogging sites were blazing hot on Sunday with talk about the EHV-1. The possibility of a fatal disease striking your horse prompts many people to take evasive action. I don't tend to get too excited about internet rumors and reports of horrible news until I get a first hand account of what is happening. And even then I don't panic. I also like to hear it being said from an expert. I scoured the internet for non-inciting news yesterday and landed on several blogs and sites that gave honest information that didn't seem to exaggerate the seriousness of the "outbreak." If you're interested in reading some of these posts, scroll down to the bottom of this post.

Many of you may not know the difference between Equine Herpesvirus-1 and Equine Herpesvirus Myeloencephalopathy. First of all, there are actually nine equine herpesviruses, but only three of them, EHV-1 (the one we're worried about), EHV-3 (which causes a venereal disease), and EHV-4 (which causes a non-fatal upper respiratory tract infection) pose a serious risk to domesticated horses.

The vaccine that we give for EHV-1/EHV-4 (Rhinopneumonitis) does not protect against EHM. There is no vaccination for EHM. Once affected with EHM, the standard form of care is simply supportive. Treatment may include intravenous fluid and anti-inflammatory drugs.

By about age two, many horses become infected with EHV-1 by contact with their dam. The virus is usually inactive, but may become reactivated by stress or contact with an affected horse. EHM is caused when the EHV-1 undergoes a mutation of the genome. [a very, very simplistic explanation!]

So what can we do about EHM? Interestingly, the literature I read strongly urges horse owners to NOT remove any horses from a site where a suspected case of EHM has been present until cleared by a veterinarian. Oops. That's what just happened. So what do we do now? Don't share tack, brushes, feed buckets, or any other communal items. Wash your hands and change clothes if you even suspect a horse might be ill. The disease is spread by horse to horse contact. DON'T allow horses to touch noses.

All the websites and blogs are reporting essentially the same thing. A case or two of the nuerologic version of Equine Herpesvirus-1 have been confirmed with a few other horses being treated as though they are positive. Most experts are recommending a quarantine period for animals suspected of being infected. The next few days should reveal a more complete picture.

For More Information:

This is a brochure from the US Department of Agriculture that gives a very clear and easy to understand explanation of the Equine Herpesvirus. It's the most informative piece I've seen. You can access the file here, scroll down and download the pdf, or view the file in the window down below.
This one is from the American Association of Equine Practitioners, click here.
This one is from Equus, click here.
This one was issued from the California Department of Food and Agriculture, click here.
This one is from "Quarter Horse News", click here.
This one is the National Cutting Horse Association's Facebook page, click here.

equine_herpesvirus_brochure_2009.pdf
File Size:	3796 kb
File Type:	pdf

Download File

Cheryl Jones

5/18/2011 03:59:54 am

Dear Ms. Sweaney

Just for the sake of discussion, EHM is a manifestation of EHV-1, and it's not quite accurate to say that there is no vaccine for it. The vaccination is to prevent contracting the virus, therefore protecting the horse from all manifestations of the virus. This is generally referenced as "neurological" manifestation of the virus.

Feel free to write back
Sincerely
Cheryl Jones

Karen

5/18/2011 12:28:18 pm

Cheryl,

Thank you for commenting. The blog and website are really intended to be a forum for sharing information. I do not claim to be an expert at anything and hope that people with more knowledge and experience will share what they know. Hope to hear from you again!

KS

Gloria Beduhn

5/22/2011 05:17:46 am

When you talk about a mutated EHV-1 virus (in this case, EHM), you're talking about a new virus. Just like human flu viruses, the old vaccines don't cover the new mutation. So how can the standard rhino viurses protect againt the mutation?
I don't have the link for the following quote anymore, but it was from some California website:
"In a California outbreak of neurologic EHV1 infection, horses vaccinated with either type of vaccine within the previous year were 9–14 times more likely to develop neurologic signs than non-vaccinated horses. Because the vasculitis associated with the neurologic form is immune-mediated, vaccination after exposure raises concerns of producing a more severe disease. Consequently, vaccination in the face of a confirmed outbreak of EHV1 neurologic disease has been controversial."

Karen Sweaney

5/22/2011 06:21:05 am

GB - Thank you for sharing! The purpose of this blog, as I've stated before, is to share information about equine health, dressage, and endurance riding, particularly as it relates to equine health!

There may be some validity to the statement that you posted above. We are currently having a discussion on the Bakersfield Vet Hospital Facebook page with Dr. Blanton. Here is a copy/paste of something she wrote the other day:

"None of the EHV vaccines available are particularly protective against the EHM strain, and there was some talk during the last outbreak that frequent boosters with those vaccines may make horses more susceptible to developing symptomatic EHM if they become infected. That said, the high antigen vaccines (Pneumabort and Rhinimmune) MAY be protective and can be boostered as often as every 90 days. They are also very reactive. In most horses 6 months is a very appropriate interval. I don't think the potential benefit of boostering more frequently would outweigh the risks or cost in most cases."

-Karen

Gwen

5/22/2011 12:12:36 pm

It is incorrect to say this is passed by horse-horse contact, and mention touching noses. While this may be true, the correct thing to say is that this is both droplet- and aerosol- transmitted, so horses need to be a lot farther away than nose-nose. Recommendations I've read mention at least 30 feet distance.

5/22/2011 12:18:35 pm

Also, this is not about a "case or two". There are almost 40 confirmed cases reported officially now, and a total of about 1000 horses have been considered "exposed". A total of 174 facilities in the US and Canada are considered exposed and under quarantine, either voluntary or madatory. This is all on USDA's Animal and Plant Health website.

The issue is to stop transmission now, in these next couple weeks, so this does not grow.

5/22/2011 11:11:47 pm

Gwen - thanks for writing and sharing!

You took me to task for a couple of my statements ("a case or two" and "nose to nose contact"). This particular EVH-1 post was written the morning after the cutting show here in Kern County. At that time, there was only a case or two of EHM that had been confirmed. Now, more than a week later, that number has certainly grown. I am not sure where you are, but here in Bakersfield, all the riders in my area have voluntarily agreed to remain on their barn's property. No one wants this to spread, or last any longer.

I write for a wide audience, some readers are not even horse owners. I often describe things in the simplest of terms so that everyone understands what I am trying to say. Am I always successful in getting my point across? Probably not. Do I bore some people with my simplicity? Definitely. My very first blog post said I would. So, while nose to nose contact might be an over simplified way of describing one way to pass infectious diseases, it is something that non-educated horse owners do all the time.

I hope you'll continue reading and I certainly hope you'll continue commenting.
- Karen

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Not-So-Speedy Dressage