Join us for this timely episode of StallSide as equine neurologist Dr. Steve Reed breaks down the recent EHV-1 outbreak—what happens when a horse is exposed, how the disease progresses, and which signs matter most. He also highlights the key prevention measures every barn should follow, from smart vaccination protocols to strict biosecurity and quarantine practices. Clear, practical guidance from one of the industry’s leading experts.
Today's episode of the StallSide Podcast was brought to you by Rood and Riddle Veterinary Pharmacy.
Dr.
Reed, welcome back to StallSide.
Glad to be here.
Thanks for inviting me.
Yeah, well, thanks for taking time.
We know you've got... With the holidays, you've got stuff to do.
Yeah.
Serious topic this morning.
Equine herpesvirus has been an outbreak, unfortunately, seasonally.
This is something that occurs about this time of year.
That's the biology of the virus.
But fill us in on the details.
Talk to us about the condition and what's going on.
Well, I think, you know, you hit it really well right at the very beginning.
You addressed the fact that it is an important disease, and it's seasonal.
And certainly, a lot of the respiratory viruses, and that's the main way that equine herpesvirus is going to be spread.
Remembering that there are more than one herpesvirus, but one in four seem to be the ones that we're most worried about.
Four, because it's going to be primarily respiratory, probably not a big deal.
But the EHV-1, this is the one that's so timely right now.
Because this virus, which is spread and transmitted by respiratory close contact, respiratory secretions, but it can invade from the respiratory system of the epithelial cells there and evade the immune system and get to the central nervous system.
And that's when the problems arise.
So there's been an outbreak at a show out west.
What would I see in my horse if my horse was affected.
Say it had been to the show, was in contact, or as you mentioned about respiratory spread, or even like fomite, people's hands touching horses.
What would I be seeing in my horse.
Well, the big things that you're going to see in your horse are going to be fever.
So that's something you need to look for.
The most difficult thing about it when they show the neurologic signs, and I jumped ahead, but we'll come back to that, is that often the febrile episode prior to the neurosigns is a couple of days earlier.
So if your horse wasn't acting sick, you might miss that fever.
But that's certainly going to be one of the things you need to do.
And then just like any other respiratory virus, you're going to be seeing things like coughing, sneezing, snotty noses, that kind of thing.
And because of the fact that it is a virus, respiratory virus, often multiple horses might be involved.
But let's focus on your horse because that's what you asked me.
And in your horse, you know, you might get a fever, you might get a snotty nose, you might get some other coughing or other signs.
But if you're unlucky enough for it to get neurologic signs, the next thing you're going to see is some degree of neurologic deficits.
Often, it's an ascending sort of a paralysis.
So they often start with pelvic limb weakness, urine dribbling, poor tail tone.
Those are kind of some of the highlights that you might see.
But remember, the virus, it's the big thing that this virus causes is intermittent small areas of thrombosis.
So it's stroke like, so you can have very acute onset, mostly in the spinal cords, you're not going to get something like a stroke that you might see in a human, but you're going to get that there is some degree of similarity to the lesions that are in fact, thrombi or little blood clots.
So how's this disease going to progress.
You mentioned that it's sort of like an ascending paralysis may start with hind limb issues and urinary incontinence.
How does it progress.
Does it always progress.
What are the signs that we're getting in trouble.
So you're in trouble as soon as you see neurologic signs.
So you got to be worried about it right there.
However, many times the horse, its immune system can kind of get it in check and hold it in check.
One of the things that a lot of the research that's ongoing right now is what is unique about the immune response.
So number one, how are we going to stop it at the nose.
Well, if you get a respiratory virus, you know, the first thing that's going to help us block it are interferons.
And interestingly, Grayson research right now is working on some vaccines, and we'll come to those here in a minute, some studies on that.
But they're also looking at the interferon 3s.
So a little different type of an interferon that looks like it might modify the immune response against equine herpes virus.
So to go back to answer the direct question that you asked me, what are you going to see.
So you might see neurologic signs that could involve anything.
What have I seen over time, I've had horses with cerebral signs, I've had horses with unilateral thoracic limb involvement.
And then I've had, as I described earlier, the what typical progression is that poor tail tone, urine dribbling, fecal incontinence, and ascending paralysis, maybe even dog sitting.
So if your horse has neurologic signs that might start quite subtly, but over the next five to seven days, and one of the things that's unique about this virus is, it appears to be very able to replicate very rapidly.
So that replicative aggressiveness, when the virus does that, it can move rapidly from cell to cell and from one spot in the body to another, going from the respiratory system to the central nervous system.
And you mentioned again, dog sitting, these horses can progress to recumbency, right and not and not get up.
And so how serious is that.
And do those horses that become recumbent, do they get over this.
Or is that a pretty grave sign.
That's a very grave sign.
There are some horses that have gone into recumbency that in fact, with time have in fact survived, but you're going to be looking at a lot of nursing care for a long time, days to weeks.
And, you know, and then they're going to have all sorts of complications, pressure sores, that you know, that's probably the biggest one.
But then they might also develop pneumonia from being down and recumbent for a long time.
So it's quite problematic.
So in response to, you know, do the horses ever survive.
Yes, but not likely once they have become recumbent.
And if they become recumbent and have either cerebral or cranial nerve deficits, the prognosis just continues to worsen.
So back that up just a little bit.
What about when they first start.
What if they just start showing mild neurologic signs.
What's the prognosis then.
So if they just have mild neurologic signs, and you catch them at that time, you know, probably the one of the things that you might want to do, then there are a number of things, some degree, some people think a little bit of anti-inflammatory, in particular, corticosteroids might be helpful at that time, because of the fact that the pathology is like a thrombi or thrombus.
Similar to what I said, with stroke like signs, you might put them on heparin.
So there's literature out there showing that that can be beneficial.
So early on, and then you've got all the antivirals, valciclovir, ganciclovir, you know, aciclovir does not get well absorbed in the horse.
So that's probably not going to be a good one.
But some of the other ones will in fact, in the metabolism will produce and give you aciclovir at a level that can be helpful to treat the horse.
It sounds like specific treatments for this condition are limited by its nature of being a virus.
You mentioned some of the antivirals.
You mentioned some anti-inflammatories.
What about supportive care.
Because of these horses, if they have neurological deficits, gait deficits become recumbent.
How intense does that supportive care have to be.
What are the things that people need to be prepared for if their horses go down this path.
I think the supportive care is probably oftentimes all you can do.
And that's probably going to be extremely important.
So what are you going to do is you're going to make sure if they're having difficulty with poor tail and anal tone, or they're dribbling urine, you got to be worried about, are they going to develop cystitis or, you know, some problem that might even be go beyond that, and they send up even to the kidneys, but you got to be concerned about that.
So nursing care, keeping them clean, keeping them in a good, clean environment.
You know, one of the other things is if they have the virus, you need to keep be aware that people who are in contact with those horses can carry that virus to another horse.
So you need to have those horses in a quarantined area.
So they need to be segregated from other animals.
And because it's primarily spread by respiratory, usually 40 feet is probably a good enough distance.
But the key thing is, are the people, you need different people that are going to do a lot of that nursing care, get the feed to them right in front of them, get good, clean hay and water in front of them.
You know, if they develop any kind of pressure sores from recumbency, make sure you take care of those things.
And then you might even have to put a urinary catheter in to keep them from scalding and everything, get that urine away from the body to prevent a lot of those secondary problems.
So if I had my horse at a barn and a horse was positive at that barn, how should we act.
I think number one, start taking your horse's temperature twice a day, morning and night, make sure that you know whether or not your horse is going to have a problem.
Keep the horses as far away from any horses that you know have that.
So take the infected horses or ones that you know are positive and move them to a separate location.
Then for a few days, at least, if possible, don't start moving all the other horses that are in the barn around.
Let them stay in their stall and just, you know, not that they can't stay there forever, but give them a little bit of a break from moving them around until you have some idea of whether or not it was just one case or more than one has been exposed.
So keeping them separated is going to be a good idea.
Some people think that that is the time when the antivirals, if they're going to be effective at all, might be the most effective.
The other thing that has been shown to be helpful early on is non-steroidal anti-inflammatory drugs, butanamine, drugs like that, Equioxx, things that are going to be potentially beneficial.
Do you start those as soon as they get a fever or earlier or later.
I think as soon as you, if you know there are positive horses in the environment, you know, it might not be a bad idea to start them, you know, right away.
But certainly once you've seen a fever.
So what's, what's the incubation period of the virus.
So if my horse has been exposed, when can I go, you know, we've quarantined him.
How long before we say we're good.
We, we used to say, you know, 48 to 72 hours, probably 72 hours gets, you know, this, but the virus itself can, it can have some different mutations.
And some of those mutations result in the virus being able to replicate very rapidly.
In those cases, it looks like the incubation period is quite short.
Like there have been outbreaks in which less than 24 hours, you got one horse infected and bam, bam, bam, they just keep moving down the line.
Generally, if you've got a horse, and it's not showing any signs after exposure by 72 to 96 hours, you can, you might not be totally out of the woods, but you can start feeling pretty comfortable that, you know, perhaps you didn't, if it did get an exposure, it had enough protection that it's not going to develop signs.
So say your horse went through this condition, had the fever, maybe had some mild to moderate neurological signs, did not become recumbent, nursing care, you get it through plus minus some of the treatments you've talked about.
How should that horse be handled in that convalescent phase.
And how do you manage that horse going forward for the rest of its life.
I think, well, number one, as far as how to handle it, that's in the immediate period, you know, that the diagnostic testing for equine herpesvirus is usually going to based on nasal swabs and doing PCR, and you're going to be able to look at the cell counts on the PCR, the replication cycles.
And so if they start getting longer and longer, so it takes 40 to 45 cycles before you get a positive, then you know that there's a pretty low viral load.
If you get it, you know, and you know, much shorter number of of replications, then you've got a real high viral load.
So as far as the horse has gotten through that and has survived, you know, I probably would handle that horse like any other.
I'd make sure that it gets routine vaccinations at appropriate times, doesn't need to be, you know, changed a lot.
Now, one of the things that we're really, really concerned about is none of the vaccines currently on the market are effective to prevent equine herpes, myeloencephalopathy, none of them.
There's even debate, even though we use it primarily to prevent abortions, about whether it's going to be perfectly effective there.
But, you know, that's for a different topic.
But the reality is right now we need some new vaccines and there's a lot of work underway on doing that.
And why did I go to that right now.
Because you asked in part, you know, how would you handle that horse going forward.
And I think, you know, now that you've got it through the crisis, you've got to make sure that you're going to keep it on a regular, well vaccinated, you know, as good of preventative medicine as you can, you know, invoke or use.
And I think something people should be aware of is that like all herpes virus, infection is for life.
And, you know, the virus becomes latent and, you know, it may not cause any problems, but it's always there.
And the thing with herpes virus is most horses are infected with one of the herpes virus very early in life, carry it for the life, never have a problem.
You bring up a good point about vaccination because an outbreak situation of what's going on at the moment, one thing that's done is actually to potentially vaccinate, knowing that it may or may not be of any efficacy whatsoever.
But it is something that I think is rational to try to raise the level of antibodies the horses have that potentially hopefully will make it more difficult for the virus to establish a problem if the horse is exposed.
You also touched on diagnostics as well.
What would your diagnostic plan be for the horse.
You mentioned nasal swabs.
You mentioned blood sampling.
When abouts in the progression of disease is that going to be effective.
And when may those tests miss the virus within the horse.
Well, all of the tests, you know, could miss it, unfortunately.
But early on in the disease, the sooner you can do the nasal swabs and get PCRs, then the more the better you are.
Follow that up.
If you get a positive on PCR with virus isolation, that's going to take some time now.
Interestingly, in one of the outbreaks that I was involved with that was all the way back in 2003, that virus was replicating so rapidly that we were able to see it on two or three days afterwards.
When you go to blood tests, you know, on the other hand, where you're looking for antibody in the blood, that might take, you know, a couple of weeks in between because you may want to do an acute, followed by a convalescent serology to see, you know, where the antibody is and whether it's going up or down.
So PCR is going to be your friend early on in the course of this disease.
You're going to look at that sort of soonest and then follow that up with virus isolation.
Those are going to probably be the key things.
And then serology, while it can be helpful, it's probably not going to be the immediate thing that is going to give you the immediate answer that you want to know where you are in the course.
So what would be your elevator speech to somebody that has heard the news that there is herpes virus affecting some horses at a competition.
What would be the thing that you would sort of say to somebody, say in Kentucky here, about what they should be looking for and how they should respond to this.
Well, number one, I think, you know, sanity is always important, so remain as calm as you can and start thinking in a logical fashion.
You know, as was mentioned earlier, once infected, they're going to be infected for life.
So recrudescence of the virus in any horse is always a possibility when they're undergoing some stress.
What are stresses.
Could be another disease, could be transport.
There are a lot of different things that can be stressors.
So, number one, you know, be a little bit calm.
Number two, then start reviewing the history.
Review the history for your own horse and for other horses that are in the stable.
Have any of them been in a location near where the outbreak occurred.
And, you know, would they have an opportunity to get exposed.
And so you need to think about that.
If there's, you know, no horses that have moved back into the state, well, then you probably can be a little calmer and a little less concerned that your horse is likely to get exposed.
But because it is a seasonal disease and there could be other horses, it never hurts to then also tempt the horse at least once a day and ideally twice a day.
And, you know, those are probably the key things that I would say.
Yeah, and I think you brought out one is sanity.
Don't panic.
But the other thing, too, is sanitation.
Right.
And not only is it by direct contact from horse to horse, droplet spread through aerosol, it's also hands, right.
Fomite spread.
And so alcohol, hand sanitizers, gloves, and just basically good, solid biosecurity for the barn to minimize the chance that things are going to spread from horse to horse.
And you're exactly, you're exactly right.
You know, just keep a cool head, watch the news.
But there's two different responses.
I mean, there's a whole array of responses.
On one end, you have the panic, but on the other end, you've got a just as big a problem with people who don't think it's a big deal and don't pay attention to it.
So you've got to you have to take it serious.
And the biggest thing is not move your horses around and expose other people to it or other horses to it.
Yeah, I think it's like, you know, the thing is to try to run away from trouble.
So it is a strong drive for people to pull the horse out of the barn and take it somewhere.
Well, that's how the plague got around Europe a few times, right, is that people would move from the disease and take it with them.
And you don't know your horse is infected because it may not be showing any signs.
I mean, and you've hit the nail on the head.
Tempt those horses twice a day.
The first sign of fever, you start to really focus on that animal and see what's going on.
Yeah, because you're right.
The first people's first response is to get their horse away.
But what they do is they bring the disease with them.
Yeah, it's one of those greater good moments.
Right.
And I think that's sort of what happened in this outbreak.
Right.
There were horses at one venue that were scheduled to go to another venue.
They did not know yet that they had already had the exposure.
And so now they went to a new venue.
Now, you know, the biosecurity from that point on, I think in every competition, whether it be racing, showing, barrel racing, whatever it is, you know, I think it's an obligation of those individuals in charge of the facility to have a biosecurity plan, have it ready in advance of, you know, what are we going to do should something happen.
I believe in this case, you know, the horses, you know, knowingly or unknowingly got dispersed very rapidly.
And the last big outbreak, the one that's been out there from Ogden, Utah.
Well, that that was it.
You know, the horses were sort of allowed to go not only all over the this country, but into other countries as well, and the things just went bad.
So if you have a horse that develops any viral disease and they're at a facility where there are a lot of other horses able to get exposed, the facility and the owners need to, at that time, think about it, move the horses into a segregated venue, the ones that are appearing sick, and then leave the other ones right where they are, tempting them with the idea that any that get sick are going to get moved to the quarantine area.
But to sort of immediately shut down and tell everybody you've got to be out of here within 24 hours, that may not be the best thing because you might move the virus all over the place.
Right.
Yeah.
I think the policy is, as you brought up horse shows, is you need to consider that your horse is the cleanest horse in the barn and your job is to keep it that way.
And, you know, to quote Presidents, the price of freedom is eternal vigilance.
Right.
You can't look at things too closely.
Steve, thanks for coming in to see us today.
This is very topical and we appreciate your time filling us in on the latest with what's going on.
Yes, my pleasure.
I think it was good to have you.
Yeah.
Always great to be here.
Thanks.
So that was Stallside's special report on equine herpesvirus.
We've been talking to Dr.
Steve Reed.
Stay safe out there.
See you next time.