Merck Equine Partners in Practice Magazine: Fall 2021

ISSUE NO. 5 | Fall 2021

MAGAZINE

EPM: A Mystery Worth Solving 06

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RON'S CAMPFIRE

SCAN HERE TO SAVE TIME AND MONEY

10,000 AND COUNTING

It Seemed like a Good Idea at the Time...

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—and Improve Horse Health

Reasons Equine Veterinary Medicine Is so Rewarding

Featured

EPM: A MYSTERY WORTH SOLVING The causes and diagnosis of EPM may not be straightforward, but the need for a proper workup is clear.

By Nicola Pusterla, DVM, PhD, DACVIM University of California, Davis, School of Veterinary Medicine

U

nlike most infectious diseases, equine protozoal myeloencephalitis (EPM) is not black and white.

The ‘gray’ areas around this disease begin with the basic question of what causes EPM in the horse, then continue into diagnosis.

Thankfully, our approach to diagnosing EPM has grown along with our understanding of the causative parasites. Let’s take a closer look at what we know about identifying and diagnosing EPM, one of the most common infectious neurologic diseases of horses in North America.1 3 causative parasites Our knowledge surrounding the organisms that cause EPM has grown significantly since the 1970s when the disease was recognized—but we still have more to learn.

show neurologic clinical signs.2 We continue to study this phenomenon to explain why most horses exposed to the organism can mount an immune response and develop antibodies, but some cannot.

Neospora hughesi Over one-third of healthy horses tested for N. hughesi in the U.S. are seropositive.2 Once in the horse, the organism stays forever, making the horse an intermediate host. N. hughesi is effectively maintained in the equine population through vertical transmission – from dam to offspring. Some horses with neuronal neosporosis experience co-morbidity with metabolic, endocrine and other chronic infectious diseases.

It is thought that these co-morbidities suppress the immune system enough to allow for an effective recrudescence of the dormant N. hughesi with subsequent possible neuroinvasion.

Toxoplasma gondii

Sarcocystis neurona

A well-recognized protozoal organism in humans and other

Strangely, 78% of healthy adult U.S. horses have S. neurona

mammals, T. gondii can play a role in some EPM cases, we just

exposure evident in their serum sample but may not

don’t know exactly how. Two studies document a possible

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association between T. gondii and EPM, one of which was done by our team at the University of California, Davis. This study found a higher likelihood of elevated serum titers for T. gondii in suspect EPM cases.3 There is more follow up to be done.

Navigating the diagnostic challenges The complicated causes of EPM can make the temptation to 'treat and see' without a complete diagnostic picture tough to resist. However, with so many diseases causing clinical signs similar to EPM, it’s an urge practitioners must avoid. If a horse has a disease other than EPM, we waste money and time.

What defines an EPM suspect case?

The best initial diagnostic step is a combination of reviewing the horse’s health history and performing a thorough physical and neurologic exam. Any region within the central nervous system (CNS) can become parasitized, and the clinical signs may vary depending on which part of the nervous system is impacted. The most common clinical signs include asymmetry, focal muscle atrophy, ataxia and dysmetria.

The basic ‘if-then’ scenario in Figure 1 can help you gain a clearer picture of a proper diagnostic workup in a suspect case.

FIGURE 1 Upon physical and neurologic evaluation: 1. Does the horse have a history of EPM or has EPM been diagnosed in the resident population?

A

Yes

B

No

2. Is the horse exhibiting asymmetrical weakness and focal muscle atrophy?

A

Yes

B

No

3. What is the immune status of the horse?

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A

High-stress, performance, travel, weaning, etc.

B

Presence of metabolic, endocrine and/ or other chronic infectious diseases

C

Age-related immunosenescence

D

Normal

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If the horse appears to have a musculoskeletal condition such as lameness or if clinical signs point to a neurological disorder other than EPM, there is no need to test for EPM. If, however, you answered yes to the questions in Figure 1 and the horse’s immune status may be compromised, antibody testing is recommended to further differentiate EPM from other neurological diseases.

Antibody testing—blood or cerebrospinal fluid (CSF)?

Evidence of intrathecal antibody production is the most accurate way to support an EPM diagnosis. However, blood is a good screening tool. If serum comes back negative, likely there is no infection or recent infection.

EPM can generally be ruled out and you can proceed down your list of differentials. A rare exception would be a very acute onset prior to antibody production, in which case a retest in 10 to 14 days is warranted.

Because 78% of healthy U.S. horses are seropositive to S. neurona and 34% to N. hughesi,2 a positive serum test result presents a ‘gray zone.’ To more definitively rule out (or in) EPM, a CSF tap is recommended. If the CSF sample is negative, EPM is ruled out and the practitioner should proceed to the next differential diagnosis. If the CSF sample is positive, consider it a pretty strong case for an EPM diagnosis.

Be aware, a positive CSF result can happen for reasons other than antibody production within the CNS. For one, blood contamination. If there is a high blood titer to S. neurona, for example, this could give a positive result from bloodderived antibody and not production within the CNS. Therefore, current best practice consensus is to collect spinal fluid and a blood sample and compare the antibody titers in each to determine if there is evidence of a CNS infection.

This is done by evaluating the ratio of antibody titer in serum divided by antibody titer in CSF. Tricky disease. Tricky diagnosis EPM got you scratching your head? Take heart. Each clinical presentation is different, and the best way to outwit this disease mimicker is with a solid dose of due diligence.

There are no shortcuts when it comes to doing a proper EPM diagnostic workup. Look for hallmarks of clinical disease in your physical exam and don’t shy away from the need for immunodiagnostics to get to the root cause.

Merck Animal Health

Get the scoop on EPM recovery: Effectively treating EPM doesn’t have to be difficult. Reach for PROTAZIL® (1.56% diclazuril) Antiprotozoal Pellets* • Goes to work fast (within 12 hours) —no loading dose required4 • The only FDA-approved alfalfa-based top dress pellet for the treatment of EPM, proven safe and effective • No mess, no fuss—easy to administer and highly palatable

Merck Animal Health

HORSE TIPS Timely Health Tips to Share with Horse Owners Veterinarians often face the eager client who confidently walks in and says, “Doc, I need this horse tested for EPM,” or “I’m pretty sure it’s EPM. Can you get him started on an EPM treatment?” Share these points to reinforce the importance of diagnosing EPM before treating it.

Why an EPM Diagnosis Is Important 1. Timing is critical. The earlier disease is caught and treatment begins, the better the outcome for any horse showing signs of neurological disease.

2. EPM can be the “master of disguise” and mimic many neurologic diseases.

It’s important to evaluate all potential causes of the horse’s illness before rushing to EPM testing or treatment.

IMPORTANT SAFETY INFORMATION: Use of PROTAZIL® (1.56% diclazuril) Antiprotozoal Pellets is contraindicated in horses with known hypersensitivity to diclazuril. Safe use in horses used for breeding purposes, during pregnancy, or in lactating mares has not been evaluated. The safety of PROTAZIL® (1.56% diclazuril) Antiprotozoal Pellets with concomitant therapies in horses has not been evaluated. For use in horses only. Do not use in horses intended for human consumption. Not for human use. Keep out of reach of children.

Reed SM, et al. Equine Protozoal Myeloencephalitis: An Updated Consensus Statement with a Focus on Parasite Biology, Diagnosis, Treatment and Prevention. J Vet Intern Med 2016;30:491–502.

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3. More than three quarters of healthy U.S. horses are carrying antibodies to S. neurona —the primary causative organism of EPM— without showing clinical signs. Only a very small percentage (<1%) of horses succumb to clinical disease. 5 4. The horse’s history is important, as is a physical and neurological examination along with proper antibody testing to rule EPM in (or out). We cannot rely on one without the other.

5. Continued vigilance with regular veterinary examinations is paramount to ensuring EPM treatment success.

James et al. Seroprevalences of anti-Sarcocystis neurona and anti-Neospora hughesi antibodies among healthy equids in the United States. JAVMA, June 1, 2017, Vol. 250, No. 11 , Pages 1291-1301 (https://doi.org/10.2460 javma.250.11.1291)

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James KE, Smith WA, Packham AE, Conrad PA, Pusterla N. Toxoplasma gondii seroprevalence and association with equine protozoal myeloencephalitis: A case-controlled study of California horses. Vet J. 2017 Jun;224:38-43. doi: 10.1016/j.tvjl.2017.05.008

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Hunyadi L, Papich MG, Pusterla N. Pharmacokinetics of a low-dose and FDA-labeled dose of diclazuril administered orally as a pelleted top dressing in adult horses. J of Vet Pharmacology and Therapeutics (accepted) 2014, doi: 10.111 jvp.12176. The correlation between pharmacokinetic data and clinical effectiveness is unknown.

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NAHMS. Equine Protozoal Myeloencephalitis (EPM) in the U.S. In: USDA:APHIS:VS, ed. Centers for Epidemiology and Animal Health. Fort Collins, Colorado: NAHMS; 2001:1–46.

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Ron's Campfire #2 cattle are unspoiled by good looks, good muscling and good conformation. They match up well with my pocketbook. These heifers aren’t as gentle as I’d like, as I bought them in the fall and kicked them out on pasture before I’d gotten them used to me and a horse. I don’t feel like bringing them all to the corral just to doctor one heifer.

Besides, I’m a cowboy with horses.

Wendy, my 10-year-old mare, needs to pay for her oats and hay.

I’d turned her out four months ago, so I was sure she’d be grateful to go to work. I saddle, cinch her up, and step on. None of that Pat Parelli “Natural Horse-Man-Ship” stuff for me; I’m running out of daylight.

She jigged around a little but I like a horse with some life to her.

I have divided my pastures with one- and two-strand electric fence.

It's psychological more than anything else. As long as they’re quiet and just walking around they remember that 5,000 volts produces an unpleasant

T

here are no greater stories to be told than those of the horse lover. Pull a chair up to Ron’s Campfire to read inspiring, touching or just plain funny tales from the people who make up our equine community. If you have a story or blog you’d like to share, we’d love to feature it.

Please email Ron McDaniel (ron.mcdaniel@merck.com) to learn more or to submit contributions.

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thump. But you can’t “cowboy” This installment of Ron’s Campfire is an original piece written by Ron McDaniel himself.

cattle, as you’ll run the whole bunch

It Seemed Like a Good Idea at the Time…

That’s the way most of my stories begin before they end poorly.

When this story began, we were having a couple days of Indian summer in the Ozarks. I buy #2 heifers that are usually pretty healthy by this time of year, but I’ve got a heifer with a bad eye that I thought I’d doctor before leaving town for a week.

Well, that’s alright with me as I’m an

right through the wire and you’ll be rebuilding fence the next two days.

enlightened cowboy, trained in the ways of low-stress cattle handling and stockmanship. I throw half a bag of feed on Wendy and swing into the saddle. Hindsight is 20/20, and as I shared the saddle with a noisy feed sack, I wished I had spent more time sacking her out. I still used the opportunity to do some horse training on her. She backed up 50 yards like World Champion Tuf Cooper’s calf roping horse, and when I

chasing them down. It should be a gentler way to rope a calf or cow.

Stockmen know that a critter will mask its sickness or disease if they feel a predator is in the area. She kept her bad eye away from me, making her look almost indefinable from the other 22 black #2 heifers. Along with that, I couldn’t get her separated without stirring up the whole bunch.

repositioned the sack, she side passed like a dressage horse. I wrapped it all up by holding the sack out to the side and sent her into a spin that would have won the National Reining Horse Association Futurity.

This training, however, did not have the gentling effect on the heifers that would have made my job easier.

After calling them back toward the feed trough, and training Wendy to allow me to pour the feed into the trough while on her back (I should have considered the direction the wind was blowing before I began the process), the heifers settled and came back our direction.

As the cattle gathered round the trough, eager to get a bite from a frugal rancher, I shook out a loop, eyed the heifer with the bad eye, and let sail with the prettiest Houlihan loop you’ve ever seen.

A Houlihan loop is backwards from most roping you see in the rodeo or on TV. It’s a big loop swung in a clockwise direction and often used to rope horses in a corral or to rope cattle from a standstill without running and

Even with all the odds against me, including not having thrown a loop at anything for four months, that Houlihan sailed straight and true.

It dropped around her neck just as pretty as you please…as well as the heifer standing right next to her!

Often when you throw the Houlihan correctly, the rest of the herd hardly moves as you coil up some slack and get short on the critter you’ve roped. Apparently, roping two at once has an opposite reaction.

Heifers scattered like a covey of quail busted by an excitable young bird dog. Rope is burning across my mule hide-wrapped saddle horn as I’m trying to ride forward and give Wendy some relief.

Wendy never cared for briar patches.

As these heifers took us into a little patch, she crow-hopped her way along. Crow-hopping is a nice easy buck that just about anybody can ride. She’s not a bucker, so I feel it was simply the logic of a horse that caused her to do this. When she was up in the air, she was fine, but when she was on the ground, she got tormented with briar stickers. If you combined saddle bronc riding with tie-down roping as an event in rodeo, I’d enter up.

In the midst of all that, one of the heifers sucked back and freed herself from my loop. The other heifer was caught and none too happy. Wendy

and I eventually laid her down and hog-tied her legs. Along with Wendy having put on a few winter pounds, I realized maybe I had too. I heard a terrible respiratory racket and was worried Wendy had the heaves, when I realized it was me making all the noise.

Careful examination revealed that although this heifer had a little ringworm in her eye socket, her eyes were just fine. The heifer with the bad eye had sucked out of the loop and was watching us from a distance.

I shared this story through a text to a couple of my buddies. Dr. Bryant Craig replied with a text that he’d pitch in and buy me a dart gun that shoots a syringe of medicine right from the comfort of your pickup truck. He did emphasize that you still have to shoot the “right” animal!

Ron’s Campfire Live and in-Person at AAEP WHAT: Storytelling Nashville-style to benefit The Foundation for the Horse WHEN: Sunday, Dec. 5, 8–10:30 p.m.

WHERE: 2021 AAEP Convention in Nashville HOW: $75 ticket (includes a complimentary beverage and gift to The Foundation) Join us at this special AAEP Convention event that promises an unforgettable night of legendary storytelling performed by some of the best singer/ songwriters in Nashville. The lineup includes Grammy-winning artist Rory Feek and a couple of his hit-writing friends, Wynn Varble and Brice Long— not to mention some of our ultratalented veterinarian storytellers.

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Merck Animal Health Business Tips

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Together, they provide a complete, secure platform for streamlining recordkeeping and accurately measuring temperature fluctuations in easy-to-read graphs.

A quick scan of a Bio-Thermo microchip instantly records a horse’s temperature, identity and GPS location. When connected to the scanner, the EquiTrace app immediately uploads the information, making it accessible to everyone on the horse’s care team (including the client) with permission to view the data.

That means records of treatments, vaccines and dentals are up-to-date and on-hand anytime and anywhere. What’s more, the ability to quickly see temperature changes is especially valuable in managing infectious disease outbreaks.

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A closer look at the power of Bio-Thermo microchips combined with EquiTrace: • Increased temperature monitoring without increased staff cost. In fact, farms testing the system in Kentucky last year saved an estimate of two full-time salaries • Tracking temperature changes for an individual horse’s daily biorhythm allows changes in health status to be detected early • Horses don’t need to be restrained for temperature checks and can even be checked in the field, reducing stress on both people and animals • Digital temperature monitoring reduces the requirement for staff to handle sick animals, therefore reducing the spread of infection via staff’s hands or clothes • Instant data upload streamlines the time needed to update records and communicate with your team and the horse’s owner

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APP STORE GOOGLE PLAY

Did You Know?

10,000 AND COUNTING: REASONS EQUINE VETERINARY MEDICINE IS SO REWARDING

By Bryant Craig, DVM Merck Animal Health Equine Professional Veterinary Services

Our team reached an exciting milestone in late April. Sample number 10,000 of the Equine Respiratory Biosurveillance Program arrived at the University of California, Davis Infectious Disease Research Laboratory.

The Merck Animal Health Equine Respiratory Biosurveillance Program is unparalleled. It is recognized as the largest equine infectious upper respiratory disease biosurveillance data set ever created, including one of the largest collections of equine influenza isolates in the United States.

Working on the Respiratory Biosurveillance Program has been one of the most rewarding and educational aspects of my job.

Each day it enables us to make a real difference in the lives of horses, which is what our team is all about­—being one step ahead to help you stay current in managing equine care.

• Look to the future with confidence by reflecting on past learnings. The breadth and depth of this study reveals important trends in seasonal infectious disease incidence, allowing us to be even more proactive in caring for horses.

A special thanks goes to Dr. Nicola Pusterla and his team at the UC Davis Infectious Disease Research Laboratory, who have delivered unprecedented 24-hour turnaround for diagnostics on the 10,000 (and counting) samples submitted by our customers.

This program would not be possible without them. And we offer a toast to the hundreds of veterinarians across the U.S. who voluntarily participate in this surveillance program, submitting samples and contributing to a better tomorrow for our industry.

The Sound of 10,000 Samples

So, in the spirit of this significant occasion, here’s a roundup of my favorite learnings from the Equine Respiratory Biosurveillance Program over its 13-year (ongoing) history. I can’t wait to see what it delivers next.

• Flu matters. Among the top benefits of this program, perhaps none outweigh the advancements we’ve made in understanding and responding to increasing equine influenza cases. It seems fitting that our 10,000th sample was an equine influenza case.

• Equine medicine at its best. The program enabled us to spot the first hints of antigenic drift in the equine influenza virus and identify a new highly virulent strain.

Merck Animal Health turned this discovery into action by updating our influenza vaccines to better protect against the influenza circulating currently in horses.

• Constantly question what we think we know.

This program has overturned many common misperceptions about equine respiratory disease. For example, we now recognize that age does not define susceptibility to certain infectious respiratory pathogens. Any horse is at risk.

Listen to this recent EquiManagment Disease Du Jour episode featuring Merck Animal Health Equine Professional Services Veterinarian Duane Chappell, DVM, discussing the background, data and learnings of the Equine Respiratory Biosurveillance Program.

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Meet the Team

Q&A HANNAH KRONENWETTER SENIOR BRAND MANAGER Basking Ridge, NJ hannah.kronenwetter@merck.com

Tell us a little bit about your background.

I’m an animal lover. My family has had dogs my entire life, and now I have a dog of my own: a 1-year-old French bulldog named Tallulah. That’s one reason I was excited to work in animal health. I started my marketing career in specialty chemicals, primarily in the personal care space. From there, I moved to pharmaceutical excipients and then to animal health. I was interested in the animal health field because the concept of benefitting a group who can’t speak for themselves really means a lot to me.

If you were a horse, what type of horse would you be?

I would be an Appaloosa. They look a little unique and different and I like to think I’m kind of unique and different, too.

What's the best horse advice you’ve ever received?

The phrase, “If you fall off a horse, you get back on,” applies to everything you do in life. And now I also better understand the literal meaning.

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Outside of the equestrian world, what is your favorite hobby?

I enjoy running, going on walks and being outside in general. I also like checking out new restaurants, breweries and wineries.

How long have you been working for Merck Animal Health?

Almost one year.

What is your favorite part of being on the equine team?

I love that our team is a small, tight-knit group and that I get to interact with everyone. All the people on our team have a passion for horses. It’s more than a job. In fact, for most people on the team, it’s literally a way of life.

If there were one thing you would want customers to know about you, what would it be?

My team and I will do what we need to do to make sure our customers are informed so horses can have the best health.

The Science of Healthier Animals 2 Giralda Farms • Madison, NJ 07940 • merck-animal-health-equine.com • 800-521-5767 Copyright © 2021 Intervet Inc., d/b/a/ Merck Animal Health, a subsidiary of Merck & Co., Inc. All rights reserved. US-EQU-211000003

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