EHV-1 Outbreak Explained: Symptoms, Risks, and What Horse Owners Should Do

Welcome to Conversations in Equine Science. I'm Nancy McClain and I'm joined by Kate Acton.

And this is the podcast where we take equine research and try to make it accessible for horse owners and enthusiasts alike. Remember that with each topic we discuss, it is important to get professional advice before implementing any of the research strategies. Greetings, everyone. Welcome to Conversations in Equine Science. I'm Nancy McLean. I'll be your host for today. And today's episode is a requested one.

It's from Carrie, one of our listeners, and she would like us to look into the EHV-1 outbreak that's occurring right now in the United States. Part of her email was concerned because on social media, she has seen postings that advocate for vaccination, and then she has seen them, no vaccinations, and she has seen bleach will disinfect the virus and don't use bleach to disinfect the virus. So I've seen the same one, so we'll kind of get into it today, and thanks for listening in.

There's been so many equine events canceled all across the U.S., the equine herpes virus, particularly the myelioencephalopathy version of it. Veterinarians have been sharing biosecurity protocols, and we're just doing the best we can to stop its spread. The numbers currently affected, we really don't know, but the equine disease website came out today, which is Sunday, November 23rd, that there's been 11 neurological illnesses of this type in Texas, four in Oklahoma.

Three in Louisiana, one in Colorado, three in New Mexico, three in Arizona, and two in Washington. So slowly every day we're hearing about more numbers being added. Some horses have been euthanized. The disease can be very traumatic. And the whole end goal of this game, fighting this disease, is to avoid exposure. So, you know, one way to do that is for horses to stay home. And I would add one more thing, though, is that also low stress.

You know, a horse being in their home environment, they're usually low stress, but you can even challenge their stress levels by changing turnout routines or changing feed routines or changing their stall location, anything like that. During this outbreak, just kind of let things be, and this will be over hopefully soon, and then we can go back to competing our horses again and feeling pretty secure today.

It's safe to do so. So EHM is the neurologic form of EHV-1, and the whole entire equine herpes virus is a family of viruses that include EHV-1 through EHV-5. The most common, though, are EHV-1 and four. The Equine Disease Communication Center, you can sign up there to get updates every day.

And they have said that cases are usually limited to the respiratory version of the disease and include symptoms such as fever, nasal discharge, lethargy, and we know pregnant broodmares, it can result in them aborting their fetuses. EHV-1 causes inflammation of the blood vessels and triggers blood coagulation within the brain and spinal cord. So, neurologic signs occur as a result of a lack of blood flow and resulting damage to the brain or spinal cord.

This disease manifests as known as equine herpes virus, myleoencephalopathy. Classical clinical signs of EHM include fever, swelling, stocking up of the limbs, hind limb weakness, and urine dribbling. And just look at the lower limb. That's where you're going to first notice the pooling of edema.

In all four limbs sometimes so make sure you have a look for that in those when you feel those limbs they may be warm so you know if you can start support therapy as quickly as possible that's going to help the survival rate. It's spread through nasal discharge from the horse sneezing or snorting, contaminated surfaces result, and people, clothing, feed, water, and stalls, they all can have the virus resting on them. The incubation period is two to 10 days.

Some people have said within 24 hours it can incubate and, you know, cause an active outbreak. So EHM is why quarantine is crucial in controlling the spread of the disease because horses can be carriers of it without any clinical signs.

And a veterinarian in Texas, I went to a seminar that he had there last week, and he says there is no vaccine that can prevent EHM. So there are vaccines for EHV-1, the respiratory version, but I looked up some current research and there was Osterreiter 2023. So Osterreiter et al. 2023, put that into Google Scholar and it'll come up. And what they did is a systematic review on 1,018 papers on the vaccinations for EHV-1.

And I tell you, it was a little bit concerning because their research shows that it's not 100% effective. In fact, they call it minimally effective. But you have to look minimally as better than none. So anyway, that's why some people are opting for biosecurity protocols in place instead of vaccinations, especially if their horses normally do not compete or get around other horses. They want to keep their horse more biosecure rather than do the vaccine.

We always vaccinate the broodmares for equine herpes virus. I mean, the rhinovirus is so hazardous to those broodmares where they can lose their foals. So it's kind of important. And when he did that research, Oster Rider, it did not include broodmares. So anyway, the virus is latent in pretty much every horse. And that means the horse gets infected in its first few months of life. The virus just kind of lays dormant in the horse and hangs out there forever.

And just like fever blisters in humans. You get stressed, the horse gets stressed, and all of a sudden you've got an active case of equine herpes virus.

It can spread to other horses very quickly, especially nose-to-nose contact, sharing water troughs, people going from barn to barn with organic matter on their boots. You know, they become, the horses become infected and contagious, and then it just spreads from there like ripples in a pond. And we're kind of seeing that now every day. There's more states reporting cases.

There was also a case in Maryland, but it has been proven not to be associated with the barrel racing event in Waco, Texas, which they're theorizing that is where this all began. So anyway, the seminar I went to were for people who travel from farm to farm. And sometimes work on other horses or go to check on other horses, like in racing, you know, horses, you can have horses all over the country competing.

So some of the, I guess, information and preventatives that they gave us at this seminar was that, you know, for those of us who do hoof your tools need to be disinfected and fortunately metal is very easy to disinfect. If you have an owner who wants you to work on their horse and that horse is sick, for right now, you just have to really be careful and use a lot of good biosecurity when you're working on that horse.

Don't go from that horse to another horse without taking that extra precaution to make sure you don't spread anything to your next horse. Hydrogen peroxide is a product very effective in this and you can go ahead and and dilute it to a 70-30 or 50-50 dilution and you know spray it on your shoes spray it on your tools it does take five to ten minutes to leave it on the surface before it's they're appropriate to use again Any phenols are good products.

You know, chlorhexidine. And, you know, you got to choose disinfectants that are not destructive to metal or that are not, you know, toxic to horses or people. So another one that I have used is 70% alcohol. It will kill and disinfect the herpes virus. And, you know, I've used it on tools. I've used it on shoes. I've even used it on my tires of my vehicle because when you leave a farm, I'll pull over on the road and go ahead and spray my tires before I pull into my farm.

And I had a vet tell me that that's a good practice to do just in case you have organic matter from that other farm that, you know, stays on your tires. And that could be mud, straw, manure, you know, anything. So, you know, the virus can live on surfaces long enough between barns that you could potentially spread it.

So the seminar recommended changing shirts hats and just being mindful of if the horse rubs their noses on you that any saliva or nasal secretions you take those clothes off before you work on another horse so do not use bleach. Diluted bleach is somewhat a destructive chemical. It's not a very good disinfectant, and it's not effective against organic debris, such as dirt, mud, manure, shavings.

If you're spraying down your horse trailer with diluted bleach, you're kind of destroying the metal or the aluminum in your horse trailer, but you're not disinfecting anything. So scrub the trailer first and then spray it down. And I would suggest using a 70% alcohol solution or a chlorhexidine in a sprayer. So for metal surfaces, you can use bleach. As long as that metal surface, those stall doors are, maybe you have caps.

On your stalls, you know, metal caps. As long as they're cleaned, as long as you don't see any organic debris, it's fine to wipe the bars down or the ledges with bleach. So EHM has a lifespan of about two days on a dry surface while it increases to two weeks on a wet surface under ideal conditions. So if the horses you're visiting or working on haven't been off their property for a long time, the chances of an outbreak are very low.

However, you know, make sure the clients haven't taken other horses somewhere or had other horses visit their farm. So I think, guys, it's all about open communication, you know, admitting when you've been traveling, make sure, you know, none of their horses have been exposed or in quarantine. And then you can always reschedule the horse as soon as this all kind of quiets down.

So anyway, there you go. That's what my last seminar talked about. So, you know, I hope everybody is safe and keep your horses secure. Have any questions, you can send me a message on Instagram, nancy__mcclain7, and we'll be happy to look into it with some peer-reviewed research. Thanks so much for listening. Appreciate your time. Bye-bye. Thank you for listening. And if you've enjoyed this podcast, give us a five-star review from wherever you listen from.

Also, drop us a line or follow us at Nancy underscore McLean seven on Instagram. Thanks so much, everyone. Have a great week. Bye-bye.