EPM 101

EPM 101

Tuesdays with Tony

What is EPM?

EPM stands for Equine Protozoal Myeloencephalitis. Breaking this down into normal person-speak instead of doctor-speak, it means a small organism called a protozoa gets in the brain and/or spinal cord and causes inflammation. There are two protozoa commonly associated with EPM. These are called Sarcocystis neurona and Neospora hughesi. These little buggers are just about everywhere in the environment. They use a variety of small mammals and birds to mature until they are ready to head to a opossum, who then poops out eggs of S. neurona and N. hughesi so that those same small animals can eat them and get infected again. Most of the time the goal is to not overly affect the animals involved while carrying out your life cycle. This keeps your hosts happy, and able to continue being a good place for you to live. 

Enter horses, because horses are often bad at life. On rare occasions in horses, the organism gets into the brain or spinal cord. This also happens with diseases like Eastern Equine Encephalitis, and West Nile Virus. They aren’t supposed to get into the central nervous system. When they do, they can’t replicate like they’re supposed to, which means they can’t complete that great circle of life. The important thing to know is that this happens in less than 1% of horses exposed to EPM. Read that again: Less than 1% of exposed horses!

What Does an EPM Horse Look Like?

My Docs talk to lots and lots of people who are sure their horse has EPM because of behavior changes, or poor performance, or lameness, or any of a million different things. What EPM horses most commonly look like is muscle loss in one spot. Because EPM most commonly affects a spot in the spinal cord, it stops the signal coming from the brain to a muscle. That signal also tells the muscle to stay all muscley and pumped up. When the signal stops, the muscle goes away, or atrophies. 

For EPM horses, this occurs in one particular area, and only on one side. If you think about it, that makes sense. The organism won’t line itself up perfectly on the centerline of the spinal cord and cause even muscle loss on both sides. If it is affecting a big enough area to hit both sides of the body, it will be way worse on one side than the other. This is a hallmark of EPM horses. They are never symmetrical. Almost always, only one side of the body is affected. In the rare case both sides are affected, one side will be way worse than the other. 

This means the first clue for my Docs is a sudden area of muscle loss. Some horses aren’t as obvious, and may present with subtle neurological signs like tripping, or sudden difficulty turning one direction or the other. Again, my Docs are going to look for areas of muscle wasting associated with these signs. They’re also going to do a very thorough lameness and neurologic exam. EPM horses will display neurological symptoms as opposed to lameness symptoms. This can sometimes take a lot of pushing, pulling, walking in weird ways, and putting horses in odd positions to determine. Luckily, my Docs are persistent.

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Testing for EPM

Here is where the really sticky widget comes in. Conclusive testing for EPM simply can’t be done by blood test, and here’s why: if the blood test is positive, it just means your horse has been exposed to EPM, it doesn’t mean it’s in their brain or spine. If the blood test is negative, it means your horse hasn’t been exposed. In many areas of the United States, it is highly, highly unlikely your horse has not been exposed to EPM. The organism is everywhere. 

“But Tony,” you say. “Does this mean there isn’t a conclusive test?” Never fear, testing can be done. But: it does require a spinal tap. This can be done as a standing procedure in 99.9% of horses. And yes, it does have to be a spinal tap. You see, the fluid around the brain and spine is special. It has huge barriers to entry from the rest of the body. You may have heard of the blood-brain barrier. That’s what I’m talking about. This means the test is only positive if the organism is actually in the brain or spinal cord. Exposure to the organism in the usual fashion won’t cause high levels in the spinal fluid. So: a spinal tap is the only way to be sure of your results.

Is it Treatable?

The short answer is yes. Very nearly all the time is the longer answer. For most horses, a diagnosis of EPM means a round of drugs to kill the protozoa. They get a strong version for at least 30 days, followed by a weaker version for several months. Marquis and Protazil are the most common drugs used for that first 30 days. Both do a great job of really hitting the protozoa hard. From there, the follow-up medication is used to actually kill the little buggers. This plan works great for most horses. 

Here’s the deal for any horse with a neurologic disease: we can only improve them one grade from their worst grade. The grades are numbered 0-5. Numbers 0-2 can usually be ridden. This means if my Docs give your horse a score of 4, they will likely improve to a 3 with the very best in therapy, AND a good response from the horse’s own immune system, which means they will be a danger to ride. This is why I said they respond nearly all the time. Sometimes the organism gets into a very, very bad spot, and/or the body responds with a big huge inflammation response, and a whole lot of damage is done in a very short amount of time. These are the worst case EPM scenarios that no veterinarian or horse owner wants to deal with. 

But My Horse Felt Better with Drugs!

Time for a giant cat pet peeve. My Docs hear this All.The.Time. My horse got better while on EPM treatment. Yep, they sure did. Every one of the medications used to treat EPM have what is known as anabolic effects. That means they work like those steroids the pro-athletes aren’t supposed to take. They aren’t as strong as the big, bad steroid injections, but they still have moderate effects. Of course your horse feels better! They were getting juiced! This my horse felt better statement is often followed by, they felt worse when they came off EPM meds, so they must have it. Now you know the real reason they felt better, and the real reason they felt worse when they stopped medication. It had nothing to do with EPM.

The moral of my tale this week is that EPM, as a cause of neurological symptoms, is not all that common. If your horse is having neurologic signs or poor performance issues, the best place to start is a good thorough physical exam, followed by a good thorough lameness exam. This gives my Docs the best chance to recommend diagnostics to determine the real underlying cause. Once they know the true problem, they can target treatments and rehab protocols to help you and your horse get back to doing what you love. If you want to see what a neuro exam is like, check out this amazing video my docs made for you!

Until next week,


P.S. If you liked that neuro exam video, there’s more where that came from! Check out my YouTube Channel for dozens and dozens of videos, as well as seminars, how-to tutorials, ASMR videos, and more!

Tuesdays with Tony is the official blog of Tony the Clinic Cat at Springhill Equine Veterinary Clinic in Newberry, Florida. If you liked this blog, please subscribe below, and share it with your friends on social media! For more information, please call us at (352) 472-1620, visit our website at SpringhillEquine.com, or follow us on Facebook!

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Myths Legends and Sketchy Ideas

Myths Legends and Sketchy Ideas

Tuesdays with Tony

The horse world is full of some crazy myths, legends, and sketchy ideas. My Docs experience them every day, and I hear my fair share of them during conversations at the clinic. I know horse people like tradition, and also The Google, but both of these are more likely to let you down than help you in a crisis. This week, let’s talk about some common myths, legends, and sketchy ideas. If you don’t want a full dose of my profound wisdom, I’ll put the moral of the story here: You should check with my Docs before you do anything.


My horse doesn’t leave the property, so no vaccines are necessary. 

There are plenty of things that reside on your property that can be 1. Vaccinated for and 2. Can kill your horse. The most common one of these is Tetanus. Horses love, and I do mean love, to get themselves hurt. Each one of those scrapes, cuts, and punctures is an opportunity for tetanus (which lives in the dirt) to go forth and multiply. Add to that mosquitos, as encephalitis delivery mechanisms, and you have several very good reasons to vaccinate, even if your horse never leaves the property. 

Rabies, and particularly rabid animals, ignore fences, as it flies in a bat, or arrives via a raccoon, fox, skunk, or any other mammal. Testing for rabies is difficult and can only be done following death. There is no treatment for animals showing signs of rabies. Sadly, euthanasia is the only answer. For vaccinated animals who have been exposed, a rabies vaccine is needed within 7 days. This thing is scary! Want to use the Google for something? Google human Rabies cases, and prepare to be scared.

Always, always, always vaccinate your horse for the basics, even if they never leave your property! The basics are: Eastern and Western Encephalitis, West Nile Virus, Tetanus, and Rabies.


If a horse is colicking, you should walk them, and if they roll, they can twist their intestines. 

There aren’t enough eyeroll emojis for me to place here to cover the level of “nope” for this one. If you, dear human, are colicky, what do you most want to do? Lay in bed in the fetal position and feel incredibly sorry for yourself? Maybe lay in that position on the bathroom floor? You most definitely do NOT want to go for a nice long walk with someone pulling you along by the head. 

Please, please, please allow your horses to lay down and feel miserable! All walking does is use up precious energy for a horse who is already colicky. I know you humans feel the need to do something, and it’s hard to let your horse just lay there. Find a safe place to put your horse so they can roll if they feel the need. Call my Docs. Fill the time you would be watching them with making sure you have your horse insurance paperwork in place, making sure your trailer and vehicle are ready to go if needed, and come up with a plan that works for you in case this is a bad colic. Bad colics require a financial plan. Use this time to run through scenarios. Trust me, it’s way easier to have an answer ready when my Docs ask, “Is surgery an option?”

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And about that twisting gut thing: It doesn’t work that way. I know it seems like it should, but in the wise words usually attributed to Dr. Neal DeGrasse Tyson, People don’t think the universe be like it is, but it do. I feel these words could be changed to, People don’t think horses be like they are, but they do. Horses roll because they have twisted their large colon and it’s painful. The twist occurs due to an impaction with a buildup of gas behind it, and the contraction of the intestine trying to move the impaction. So, the rolling doesn’t cause the twist, the rolling is a result of the twist. Make sense?

EPM, Ulcers, Kissing Spines, Lyme Disease

My horse has *insert disease* because I Googled it and the symptoms match. This one gets two myths, legends, or sketchy ideas. Also, I found this supplement on the internet that says it will fix *insert disease* and it has a lot of likes and shares so it must be good.

These, and many other diseases, are real. However, more often than not, they aren’t what’s wrong with the horse. The more common things like bad feet, arthritis, or tendinitis are causing the problem. The other problem with many of these diseases is actually diagnosing them. Let’s take EPM for example. 

There are several blood tests available. None are particularly good at telling us if a horse has EPM. They can indicate that it’s unlikely a horse has EPM, but not the other way around. If they are positive, you may as well flip a coin. That horse may have EPM, or it may have been exposed to it, and if you live anywhere in most of the United States, chances are good your horse has been exposed to it. 

To actually diagnose EPM, you need some of the fluid around the spine. That is the only definitive way to know. Lyme disease is even harder! The worst version of Lyme disease is very often negative to every test available on a living animal!! This uncertainty causes the very worst in humans to rear their ugly heads: The Snake Oil Salesman. 

I’m going to help out here because I’m such a generous cat: if a “treatment” is not recommended by your veterinarian, it’s because it doesn’t work. Even worse, if it is widely advertised on the Faceplace and has tons of comments, but your veterinarian rolls their eyes when you mention it, it’s because this product will only take your money, and not help your horse. I promise you, my Docs want your horse better, and they want to do it in the most economical way they can. Horses don’t always go in for that plan, but my Docs try their absolute hardest.

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This *insert product name* is the absolute best for wounds. Look at this picture of the healed wound I found on the internet!

This one is short and sweet. For all the effort horses put into hurting themselves, they really, really want to heal. Most of the time it’s a matter of staying out of the way of the healing process, not putting some goop in the middle of it. Ten minutes daily with a hose, and good bandaging are the keys to wound healing. Sure, my Docs will add some stuff to really dirty or nasty wounds, and they use things like Silver Sulfadiazene, or Manuka Honey to help wounds heal faster, but the cornerstone of wound care is water and bandaging.

A cat could go on and on about all the crazy ideas horse people have, but I won’t. I’ll go back to my sage advice at the beginning of this week’s blog: If your horse has something wrong, talk with my Docs. They will help figure out what’s really going on, and find the best treatment possible. And it will probably be a lot cheaper than that other stuff.

Until next week,


P.S. If you want more, the humans have a podcast on this very topic, with the same name I used for this blog. I know, I was a bit lazy, but come on, I’m a cat. Anyway, you can find it over on the Podcast Page of my website. With over 100 episodes now, you’ll likely find some other good stuff to listen to. It’s a great free resource, and it was all my idea, of course. You’re welcome.

Tuesdays with Tony is the official blog of Tony the Clinic Cat at Springhill Equine Veterinary Clinic in Newberry, Florida. If you liked this blog, please subscribe below, and share it with your friends on social media! For more information, please call us at (352) 472-1620, visit our website at SpringhillEquine.com, or follow us on Facebook!

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EPM, and Why Your Horse Probably Doesn’t Have It

EPM, and Why Your Horse Probably Doesn’t Have It

Tuesdays with Tony


Three letters that get humans in such a tizzy. It seems these letters carry some special meaning. Since curiosity is in my nature, I launched an investigation. Moral of the story: your horse probably doesn’t have EPM, but it might. Read on to find out more from this intrepid cat.


It’s Everywhere


For large parts of the United States, the organisms that cause Equine Protozoal Myeloencephalitis (now you know why they abbreviate it EPM) are pretty common. There are two main bugs responsible: Sarcocystis neurona, and Neospora hughesi. To be honest, there are probably a couple more organisms, but they are super rare. S. neurona, and N. hughesi live a complicated lifestyle involving poop, possums, birds, and possibly some other animals. The short version is that if your horse eats hay, grain, or grass, they’re likely exposed to the organism on a regular basis.


But it’s OK!


I mildly apologize if that last paragraph sent you into a panic. Just because your horse has been exposed to EPM doesn’t mean they’re going to get it. First off, the overwhelming vast majority of horses, which is 99% or higher, can fend off EPM all by themselves. To say it another way, less than 1% of horses exposed to EPM actually contract it. Their immune system does a really great job with it. If you want to learn more about this part of equine immune systems and EPM, check out the EPM podcast that’s coming out this week on Straight from the Horse Doctor’s Mouth. It’s a lot easier to digest when you listen to Dr. Lacher explain it.

The second big reason your horse isn’t likely to get it, even when exposed all the time, is that the organism has to not only get into your horse, it has to get into the central nervous system before it can cause a problem. The central nervous system is rather like Fort Knox. There’s security, and then there’s Central Nervous System security. It’s a whole different level of tough to get past! The >1% of horses who actually get EPM have an immune system (the security system of the body) that doesn’t do a great job recognizing EPM as a bad guy. These immune systems have a blind spot for the organism. Fortunately the immune system is unbelievably complicated, so it’s an uncommon blind spot.


But the EPM test was positive


Testing for EPM is an excellent illustration of things that are even more complicated than human behavior, and I find that pretty complicated. There are a few different ways to run tests for EPM. My Docs commonly start with a screening type test. Blood is pulled, and then sent to a lab in Kentucky. There they check for some markers of the EPM organisms. If that test is negative, it’s a pretty good bet your horse doesn’t have EPM. There’s a tiny chance your horse could have EPM, but if so, it’s really, really early in the process and the immune system hasn’t gotten around to making the markers that are being checked.

Now that we know what negative means, let’s talk positive. A low positive likely means your horse has been exposed to the organism, but has fended off that attack and everything is going to be alright (this is the 99% of horses we talked about). A mid-range positive means the organism is in attack mode, and without further investigation we really don’t know how the battle is going. A high positive means we really need to move on to the next phase of testing to get a handle on the battle!


Yay! More tests!


…said no human ever. But it’s really important to follow up screening blood tests to find out if your horse actually has EPM. This is done by getting a sample of cerebrospinal fluid (CSF). CSF taps are a relatively simple procedure, but can have some serious complications. We find they are best done in stocks, or with the horse fully anesthetized. This fluid is then submitted to the same lab as the blood. They do the same testing as is done on the blood. These results usually give my Docs a clear answer about the presence or absence of EPM. Since there’s a horse involved, sometimes (but rarely) the answer isn’t so clear.


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Important Things to Know


Every single horse suspected of having EPM should have a very thorough neurologic exam. During this exam, my Docs circle the horse tightly, pull on the tail, and do a wide variety of other weird things trying to determine if this horse knows where all its body parts are. The muscles are also VERY closely inspected. Muscle asymmetry is a common sign of EPM. Muscle asymmetry can also be a sign of a lameness, arthritis, and about fifty other things too, so don’t jump to conclusions!

Lots of people say, “But my horse got better on medication.” Yep. He sure did. That’s because every one of the medications used to treat EPM are also anti-inflammatory drugs, just like bute and Banamine. This means horses with some arthritis or low-level pain will get better on these medications from this “side-effect.” And they’ll get worse again when they go off these medications. That doesn’t mean they are having a relapse.

Speaking of relapse: They are pretty darn rare with EPM. Again, not saying they don’t happen, but it isn’t very common. Remember how I said the immune system is complicated? It’s also a very good learner. An infection with EPM is often enough to trigger it to fix that blind spot.

Whew. You can now cross off one thing to worry about!

Until next week ~


Want even more wisdom? Check out Straight From the Horse Doctor’s Mouth. It’s a podcast with Dr. Lacher about everything horse and veterinary. Sure, it’s missing my sarcasm, but it’s quality programming nonetheless.

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Tuesdays with Tony is the official blog of Tony the Clinic Cat at Springhill Equine Veterinary Clinic in Newberry, Florida. For more information, please call us at (352) 472-1620, visit our website at SpringhillEquine.com, or follow us on Facebook!

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