The Modern
Equine Vet www.modernequinevet.com
Your TRH Test Questions Answered Resistance to R. equi Treatment Growing New Test for Gene Doping What Causes EPM
Vol 11 Issue 5 2021
TABLE OF CONTENTS
COVER STORY
4 Your TRH Test
Questions Answered Cover: Shutterstock/Kwadrat
INFECTIOUS DISEASES
What Causes EPM in Horses?............................................................................................................8 Macrolide/Rifampin Prophylaxis for R. equi Leading to Multidrug Resistance..........14 NEWS NOTES
New Test Detects Presence of Gene Doping in Horses........................................................13 Tackling the Heat of the Tokyo Olympics........16 SPONSORED EDITORIAL
Dental Exams: Help Your Clients Realize Their Importance to Horse Health ........................................3
ADVERTISERS Zoetis Sponsored Content..................................................................................3 Arenus Animal Health/Aleria............................................................................5 Epicur Pharma......................................................................................................6 Arenus Animal Health/Assure Gold.................................................................9
Arenus Animal Health/Releira........................................................................15 American Regent/Adequan.............................................................................11 Arenus Animal Health/Assure Gold...............................................................17
The Modern
Equine Vet SALES: Matthew Todd • Matthew Gerald EDITOR: Marie Rosenthal ART DIRECTOR: Jennifer Barlow CONTRIBUTING WRITERS: Paul Basillo • Adam Marcus COPY EDITOR: Patty Wall Published by PO Box 935 • Morrisville, PA 19067 Marie Rosenthal and Jennifer Barlow, Publishers PERCYBO media publishing
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Dental Exams: Help Your Clients Realize Their Importance to Horse Health As a veterinarian you can tell a lot from these regular checks By Jeff A. Hall, DVM, Senior Veterinarian, Equine Technical Services, Zoetis
A
2019 equine dental study, published in the Journal of Equine Veterinary Science, revealed there is an established link between common horse behavior problems and abscessed cheek teeth. Periapical infections in cheek teeth are common in horses1 and will usually induce pain that horses then exhibit in their behavior.
schedule annual dental exams because they are unsure about what goes into an exam and what their horse will experience. Veterinarians have an opportunity to educate horse owners about the importance of dental exams, and the impact dental challenges can have on their horse’s well-being and behavior.
Despite this established connection between dental pain and behavior problems, many horse owners are unaware of the impact dental challenges can have on their horse’s health and performance. A 2020 equine dental wellness survey conducted by Zoetis revealed that out of nearly 4,000 horse owners from across the U.S., 73% indicated their horse was showing at least 1 behavior associated with dental pain.2 Yet 22% of respondents indicated their horse hasn’t had a dental exam in at least 12 months.2
Take the time to follow up with clients who haven’t brought their horse in for a dental exam. Reassure clients that dental exams are safe, routine procedures for their horse by helping them know what to expect. This includes how long the exam will last and what you’re looking for as you examine their horse. As part of this conversation, explain that in order to complete a thorough visualization and palpation of the mouth and teeth, the horse must be sedated. Sedation helps ensure compassionate care for the horse and precise control for the veterinarian performing the procedure.
I find that horse owners sometimes hesitate to
HELP CLIENTS KNOW WHAT TO EXPECT DURING DENTAL EXAMS
SEDATION FOR A SAFE DENTAL EXAM Sedation isn’t only for the horse’s safety. It’s also for the safety of you, your technician, or anyone handling the horse. A consistent, reliable sedative is preferred — one that provides pain control to help ensure the horse’s comfort throughout the exam is also advantageous.
in just 1 dose. It’s supported with 30 years of safety data and provides the veterinarian with predictable sedation.3 And veterinarians continue to rate DORMOSEDAN highest of all equine sedation products for reliability.3 Learn more about it by visiting Dormosedan.com.
DORMOSEDAN® Sterile Solution (detomidine hydrochloride) meets equine sedation and analgesic needs
SCHEDULING DENTAL EXAMS IN SPRING WELLNESS EXAMS Remind your clients that spring
physical exams are the perfect time to complete a full wellness check that includes a dental exam, vaccination against the five core (potentially fatal) diseases and risk-based diseases as needed, as well as a fecal exam followed by the appropriate deworming administration. Just like vaccinations and parasite control, a thorough dental exam helps set horses up for a successful and healthy year.
IMPORTANT SAFETY INFORMATION: Do not use DORMOSEDAN STERILE SOLUTION in horses with pre-existing atrioventricular (AV) or sinoatrial (SA) block, with severe coronary insufficiency, cerebrovascular disease, respiratory disease, or chronic renal failure. Intravenous potentiated sulfonamides should not be used in anesthetized or sedated horses. Careful consideration should be given to horses approaching or in endotoxic or traumatic shock, to horses with advanced liver or kidney disease, or to horses under stress from extreme heat, cold, fatigue, or high altitude. Do not use in horses intended for human consumption. Handle dosing syringes with caution to avoid direct exposure to skin, eyes or mouth. See full Prescribing Information. REFERENCES 1 Pehkonen J, Karma L, Raekallio M. Behavioral Signs Associated With Equine Periapical Infection in Cheek Teeth. Journal of Equine Veterinary Science. 2019;77:144-150. 2 Zoetis Equine Dental Risk-Assessment Survey Results. Zoetis U.S. Market Research. May 30, 2020 3 Data on file, 2020 Equine Pain & Sedation Market Research Study. Aug. 10, 2020 All trademarks are the property of Zoetis Services LLC or a related company or a licensor unless otherwise noted. DORMOSEDAN is trademark owned by Orion Corporation Orion Pharma Animal Health. It is manufactured by Orion Corporation and distributed by Zoetis under license from Orion Corporation Orion Pharma Animal Health. © 2021 Zoetis Services LLC. All rights reserved. GEQ-00676
ModernEquineVet.com | Issue 5/2021
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ENDOCRINOLOGY
Your TRH Test Questions
ANSWERED
is tough enough to monitor and treat in a controlled setting. When a veterinarian is in the field, outside factors can often throw the repeatability of the tests into doubt. John C. Haffner, DVM, Rhonda M. Hoffman, PhD, PAS, DACAN; Steven T. Grubbs, DVM, PhD, DACVIM; Kayla N. Shepard, MS;Dwana L. Neal, MBA; and Greg L. Pearce recently completed a series
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This bay mare demonstrates early symptoms of loss of topline muscle and delayed shedding on the body.
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of studies that aim to answer some common questions to put practitioners’ minds at ease.
1. How long is frozen/thawed thyrotropin-releasing hormone (TRH) effective for ACTH release?
For the first study, Dr. Haffner, an associate professor at Middle Tennessee State University, and his team tested the duration of effectiveness of frozen and thawed TRH.
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Courtesy of Dr. John Haffner
Pituitary pars intermedia dysfunction (PPID)
IN A WORLD OF ITS OWN
Researched Respiratory Support Researched and Proven as an aid in controlling IAD and RAO Recommended in the ACVIM Consensus Statement on Respiratory Disease (1)
(2)
Not all Omega 3’s are the same; use the Researched and Recommended 1500mg Purified DHA formulation. Your Clients Deserve The Best in a Non-Pharmaceutical Solution.
– Using the Best Matters References: [1] Nogradi N, Couetil LL, Messick J, Stochelski MA, Burgess JA. Evaluation of an Omega-3 Fatty Acid Containing Feed Supplement in the Management of Horses with Chronic Lower Airway Inflammatory Diseases. J Vet Intern Med 2015; 29:299-306. [2] Couetil LL, Cardwell J.M, Gerber V, Lavoie J.-P, Leguillette R, Richard E.A. Inflammatory Airway Disease of Horses. ACVIM Consensus Statement J of Vet Intern Med 2016; 30:503-515 p. 508-510.
Check with Arenus on how Aleira can help your equine patients effectively cope with respiratory and immune function disorders. See how Aleira can help you to reduce or eliminate pharmaceutical interventions.
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ModernEquineVet.com | Issue 5/2021
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ENDOCRINOLOGY
Trailering a horse will increase thyrotropin-releasing hormone levels, so blood should not be obtained for resting ACTH levels for at least 30 minutes after the horse is brought in on the trailer. “A practitioner who gets their TRH in a 5-dose vial was told that if you’re not going to use it all immediately, then you should draw individual doses into a 3-mL syringe and freeze them, then thaw them on the day of the TRH stimulation test,” said Dr. Haffner during a virtual presentation for the 66th Annual AAEP Convention. “The question then came up about how long you can thaw the TRH and keep it refrigerated before it’s not effective.” It has been said that refreezing thawed TRH could alter it enough to affect the results, so the researchers wanted to test the hypothesis in a real-world scenario. The team enrolled 10 horses and separated them into 2 groups—each group had 4 PPID-negative and 1 PPID-positive horses. They then froze 30 doses of constituted TRH at –20° C 28 days prior to testing. Fourteen days prior to testing, they thawed 10 doses and kept them at 5° C. The remaining 20 doses were thawed on the first day of testing and maintained at 5° C. “When we did the TRH stimulation testing, the ACTH concentrations were not changed out to day 56,” Dr. Haffner said. “TRH is still good if it’s kept refrigerated for 56 days.”
2. Will trailering or dentistry affect ACTH levels?
“The second study came up as a question,” he explained. “If someone hauls a horse into a clinic or if the horse had a minor procedure like teeth floating, would that affect the adrenocorticotropic (ACTH) levels in a way that would affect the TRH stimulation test?” The team took 12 PPID-negative horses and divided them into 3 groups. Plasma was collected at baseline. The first group was taken on a 40-minute trailer ride, and the second group had their teeth floated with xylazine sedation. The third group was left tied in the stall. “Four weeks later, we rotated the groups, and then rotated them again after another 4 weeks,” Dr. Haffner said. “All 12 horses were exposed to all 3 treatments.” Blood samples were taken at 15, 30, 60 and 120 minutes after the trailering or teeth floating was completed. Results showed no changes in ACTH levels in the stall and dentistry group, but trailering did cause an 6
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increase in ACTH from baseline. ACTH remained increased at 15 minutes, but levels returned to baseline after an average of 30 minutes. However, 1 horse had elevated ACTH levels until 120 minutes. The researchers recommended that blood should not be obtained for resting ACTH levels for at least 30 minutes after the horse is brought in on a trailer.
3. What is the repeatability of TRH testing for PPID?
Next up, the team wanted to evaluate TRH repeatability in the late winter and spring months in both PPID-positive and PPID-negative horses. Five positive, 5 negative, and 2 PPID equivocal horses were enrolled, and testing was done every 28 days from February to June in Tennessee (Latitude 35°, 50' 44" North). “Generally, the results were consistent,” Dr. Haffner said. “If the horse tested positive, it continued to be positive. If it was negative, it continued to be negative, and if it was equivocal, it stayed equivocal throughout the study.” However, he did note that 3 of the horses were inconsistent. One PPID-negative horse tested positive once, and another negative horse tested positive twice. One positive horse tested equivocally once. “It reminds us that it’s important to include history and clinical signs when you’re trying to make a diagnosis of PPID,” he added. “The lab data all have to be looked at. Don’t just rely on the results from a blood test before you consider a horse to be positive for PPID.”
4. How long can centrifugation wait?
After a long day in the truck, sometimes the last thing you want to do is sit and watch plasma spin. But after a practitioner obtains an ACTH sample, how long can it be refrigerated before it can be centrifuged? To answer this, the team enrolled 5 positive and 5 negative horses, drew blood in purple top tubes, and placed them in a standard refrigerator. The first sample was spun down immediately, and the rest were kept in the refrigerator. Samples were then removed and spun at 4, 8, 12 24, and 36 hours after collection, then frozen and shipped to the Cornell lab for ACTH measurement.
“What we found was that there was no variation in the ACTH levels out to 36 hours,” Dr. Haffner said. “We determined that it is safe to keep the samples refrigerated until the practitioner can return to the clinic within 36 hours. Hopefully, we’re not working 36-hour days yet, so you should be good to go.”
5. What’s the best way to freeze ACTH plasma?
The final study in the series tested the effect of various freezing protocols on ACTH plasma concentrations. “We were looking at 2 different situations,” Dr. Haffner explained. “One is the practice situation, where you might want to keep the plasma frozen over the weekend. The other is in a research situation, where you might want to keep it frozen for several months or years in a –80° C freezer.” The team took samples from 12 horses (5 mares, 6 geldings and 1 stallion) and froze them in a freezer set at either –20° C or –80°C. To mitigate the fluctuation of temperatures that occurs when staff open and close the freezer door, some samples in the –20° C freezer were also placed between ice packs.
®
“It’s been thought that if you have a sample in a freezer in the clinic and people are opening and closing the door, that may affect ACTH levels,” he said. In the short term, none of the samples showed any significant decrease in ACTH levels. The freezer packs did not appear to offer any benefit for the samples stored at –20° C. “We did see that there was some decrease in ACTH levels by 90 days in the samples kept at –80° C,” Dr. Haffner explained. “There was also some decrease by day 60 in the samples at –20° C, but there was no decrease out to 7 days.” For the specimens held at –80° C, the samples showed a 6.9% decrease in ACTH levels from baseline to day 90. “If you're doing a research project, you need to know that if you keep it more than 90 days, you might see some degradation in the values,” he said. “In a practice situation, you’re probably not going to keep it for more than a week anyway. If you get a sample on a Friday, just freeze it and ship it out by Monday.” MeV
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INFECTIOUS DISEASES
What Causes
EPM in Horses? B y
N i c o l a
P u s t e r l a ,
D V M ,
EPM THEN AND NOW A retrospective look at how far we have come in understanding, diagnosing and treating this important infectious neurological disease. In this four-part series, Nicola Pusterla, DVM, PhD, DACVIM, will guide us through a reflective account on equine protozoal myeloencephalitis (EPM), including advances in testing and diagnosing, as well as treatment and preventive measures.
Part 1 of this series provides a brief review of what causes EPM.
P h D ,
D A C V I M
Equine protozoal myeloencephalitis (EPM) was first recognized as a condition in 1976, and it remains one of the most common infectious neurologic diseases of horses in North America. A progressive disease, EPM can affect any horse and cause irreversible damage to the brain or spinal cord if left unchecked. Unlike most infectious diseases, EPM management is not black and white, which is cause for much frustration among equine practitioners. The “gray area” surrounding this disease has prevailed since it was originally discovered. As 1 mystery is solved another arises, beginning with the most basic question: What causes EPM in the horse? The main culprits
Originally thought to be caused by Toxoplasma gondii, it took nearly 20 years after the disease was recognized to identify its primary causative agent as Sarcocystis neurona. Today, we know EPM can be caused by both S. neurona and Neospora hughesi. It may come as a surprise, however, that T. gondii is back in the mix as a possible cause (although less is known about this organism’s role). Table 1 depicts the common characteristics of each parasite that can cause EPM.
Sarcocystis neurona
The most common cause, S. neurona encompasses almost every single clinical presentation and 8
Issue 5/2021 | ModernEquineVet.com
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INFECTIOUS DISEASES
makes up roughly 85% to 95% of cases. The strange thing about S. neurona is the sheer number of horses with exposure evident in their serum sample (78% of healthy adult U.S. horses) and do not have neurologic clinical signs. 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. Those horses that do succumb to clinical illness seem to be either immunocompromised or unable to prevent the protozoal organisms from invading the central nervous system.
Neospora hughesi
The vague and
abortion or the birth of an immunocompetent, non-affected animal that is latently infected. It is not uncommon to find a horse with neuronal neosporosis experiencing comorbidity with metabolic, endocrine and other chronic infectious diseases. It is thought that these comorbidities suppress the immune system enough to allow for an effective recrudescence of the dormant N. hughesi with subsequent possible neuroinvasion.
varied clinical signs of EPM can lead practitioners down a windy road to patient recovery.
More than one-third of healthy horses tested for N. hughesi in the U.S. are seropositive.2 It is a common organism that has spread across the U.S. and likely worldwide.1 Biologically, it is different from S. neurona. Once it is in the horse it stays there forever, which means the horse is an intermediate host. We also know that it is effectively maintained in the equine population through vertical transmission—from dam to offspring. During times of immunosuppression, such as gestation, the organism is reactivated and, in some instances, will cross the utero-placental unit and infect the fetus. This can lead to various outcomes, such as
Toxoplasma gondii
A well-recognized protozoal organism in humans and other mammals, T. gondii can play a role in some EPM cases, we just don’t know exactly how. There are 2 studies documenting a possible association between T. gondii and EPM—1 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. There is more follow up to be done in this area.
Take-home message
Making sense of the gray areas around EPM continues to be the subject of much study, but our education has taken leaps and bounds since the 1970s, when the disease was originally recognized. Much of that knowl-
While some regions of the country have a higher seroprevalence than others, overall S. neurona and N. hughesi seroprevalence in healthy adult U.S. horses is 78% and 34%, respectively.2
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Issue 5/2021 | ModernEquineVet.com
There’s nothing else like it. For more than 30 years, Adequan® i.m. (polysulfated glycosaminoglycan) has been administered millions of times1 to treat degenerative joint disease, and with good reason. From day one, it’s been 2, 3 the only FDA-Approved equine PSGAG joint treatment available, and the only one proven to. Reduce inflammation Restore synovial joint lubrication Repair joint cartilage Reverse the disease cycle When you start with it early and stay with it as needed, horses may enjoy greater mobility over a 2, 4, 5 lifetime. Discover if Adequan is the right choice. Visit adequan.com/Ordering-Information to find a distributor and place an order today. BRIEF SUMMARY: Prior to use please consult the product insert, a summary of which follows: CAUTION: Federal law restricts this drug to use by or on the order of a licensed veterinarian. INDICATIONS: Adequan® i.m. is recommended for the intramuscular treatment of non-infectious degenerative and/or traumatic joint dysfunction and associated lameness of the carpal and hock joints in horses. CONTRAINDICATIONS: There are no known contraindications to the use of intramuscular Polysulfated Glycosaminoglycan. WARNINGS: Do not use in horses intended for human consumption. Not for use in humans. Keep this and all medications out of the reach of children. PRECAUTIONS: The safe use of Adequan® i.m. in horses used for breeding purposes, during pregnancy, or in lactating mares has not been evaluated. For customer care, or to obtain product information, visit www.adequan.com. To report an adverse event please contact American Regent, Inc. at (800) 734-9236 or email pv@americanregent.com. Please see Full Prescribing Information at www.adequan.com.
www.adequan.com 1 Data on file. 2 Adequan® i.m. Package Insert, Rev 1/19. 3 Burba DJ, Collier MA, DeBault LE, Hanson-Painton O, Thompson HC, Holder CL: In vivo kinetic study on uptake and distribution of intramuscular tritium-labeled polysulfated glycosaminoglycan in equine body fluid compartments and articular cartilage in an osteochondral defect model. J Equine Vet Sci 1993; 13: 696-703. 4 Kim DY, Taylor HW, Moore RM, Paulsen DB, Cho DY. Articular chondrocyte apoptosis in equine osteoarthritis. The Veterinary Journal 2003; 166: 52-57. 5 McIlwraith CW, Frisbie DD, Kawcak CE, van Weeren PR. Joint Disease in the Horse.St. Louis, MO: Elsevier, 2016; 33-48. All trademarks are the property of American Regent, Inc. © 2021, American Regent, Inc. PP-AI-US-0629 03/2021
INFECTIOUS DISEASES
TABLE 1: Characteristics of EPM Etiologic Agents Sarcocystis neurona
Neospora hughesi
Toxoplasma gondii
Life cycle
2-host life cycle Definitive host: opossum Intermediate hosts: skunks, raccoons, armadillos, cats, passerine birds, sea otters and horses (see Figure on page 8)
Poorly characterized. Definitive host unknown but likely a wild or domestic canid Intermediate host: horse
Definitive host: cat Intermediate hosts: birds and mammals
Role of horse
Dead-end and intermediate host4
Intermediate host
Intermediate host
Seroprevalence (U.S.)
78%
34%
6.5%5
Risk factors
Age (generally young performance horses) Stress Comorbidity Exercise Environment (wooded areas; previous history of EPM on premises)
Immune compromised Older horses Pregnant animals Comorbidity
Cats on premises Immune compromised
Clinical signs
Asymmetrical weakness, ataxia, dysmetria and focal muscle atrophy (May vary depending on part of central nervous system parasitized)
Asymmetrical weakness, ataxia, dysmetria and focal muscle atrophy plus signs of co-morbidity
Synonymous with S. neurona in documented EPM cases
Notes
Horse infected by ingesting food/ water contaminated with opossum feces
Once infected, infected for life Evidence of transplacental transmission
EPM-suspect horses were 3.6 times more likely to have a serum titer of 320 to T. gondii compared with nonneurologic horses3 (Rose to 6.4 times in autumn)
2
2
edge has centered on the causative organisms and how they behave in the horse, which has proved to be key to proper diagnosis and management. The vague and often varied clinical signs of EPM can lead practitioners and horse owners down a windy road to patient recovery. A tricky disease means the diagnosis can be tricky as well. Stick with us as we unravel the diagnostic challenges of EPM with recommendations and best practices for getting to a proper EPM diagnosis. MeV REFERENCES 1. 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. 2. James et al. Seroprevalences of anti-Sarcocystis neurona and antiNeospora Hughesi antibodies among healthy equids in the United States. JAVMA. 2017;250(11):1291-1301 https://doi.org/10.2460/ javma.250.11.1291 3. James KE, et al. Toxoplasma gondii seroprevalence and association with equine protozoal myeloencephalitis: A case-controlled study of California horses. Vet J. 2017;224:38-43. doi: 10.1016/j. tvjl.2017.05.008
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4. T. Mullaney, et al. Evidence to support horses as natural intermediate hosts for Sarcocystis neurona. Vet Parasitol. 2005;133:27-36. 5. Xi L, et al. Seroprevalence of Toxoplasma gondii in horses: a global systematic review and meta-analysis. Acta Tropica. 2020;201:105222. https://doi.org/10.1016/j.actatropica.2019.105222
About the Author
Nicola Pusterla, DVM, PhD, DACVIM, is a professor of epidemiology and medicine at the University of California, Davis, School of Veterinary Medicine. His research focuses on infectious diseases and molecular epidemiology. Dr. Pusterla wrote this article series in partnership with Merck Animal Health. He was instrumental in setting up the Equine Respiratory Surveillance Program with Merck at UC Davis.
NEW NOTES
By Hannah Kleckner Hall Penn Vet Researchers at the University of Pennsylvania School of Veterinary Medicine (Penn Vet) have successfully developed a new test to systemically detect the local administration of illicit, gene-doping therapies in equine athletes. Unlike other small molecule pharmaceuticals, gene-doping agents trigger cells to produce performance-enhancing proteins, which often are more elusive to testing due to their virtually indistinguishable characteristics from naturally occurring proteins within the body ... until now, that is. Led by Mary Robinson, PhD, VMD, DACVCP, assistant professor of Veterinary Pharmacology and director of the Equine Pharmacology Laboratory at Penn Vet’s New Bolton Center, the team created and validated a quantitative real-time polymerase chain reaction (PCR) test that can detect the presence of a gene-doping agent in plasma and synovial fluid after its intra-articular administration in horses. “For the first time, we have demonstrated that a PCR test performed on a blood sample can detect the local administration of a gene therapy into the joint of a horse,” Dr. Robinson said. “While this test is currently limited in that it can only detect a specific gene therapy, it provides proof of concept that a gene therapy administered into the joint can be detected in a blood sample in a manner that is quick, convenient, and consistent with our long-term goal of deploying pre-race testing someday in the future,” she added. In addition to detecting the presence of this product in equine joint fluid after gene therapy was administered intra-articularly, they could detect it in blood for up to 28 days—a robust window of time that could be useful for prerace as well as out of competition testing, they said. “The science is closing in on those who seek to use these advancements for wrongful means; the more we learn with each study, the harder it will be for individuals who seek to cheat the system using gene-doping
Shutterstock/Lukas Gojda
New Test Detects Presence of Gene Doping in Horses
strategies,” said Joanne Haughan, Mag Med Vet, one of the lead investigators on the study This ongoing body of research in gene doping is being performed concurrently with Penn Vet’s larger multitiered, multiyear project to expand upon New Bolton Center’s equine BioBank. The growing database collects and analyzes multiple types of samples, looking for a myriad of potential biomarkers in equine athletes. With the goal of someday creating “biological passports,” researchers believe these biomarkers could also be key in detecting gene doping as well as predicting injuries before they happen. “We still have a lot of work to do to better understand the nature of biomarkers and how to fully harness their capabilities, but the science for detecting gene doping is getting there and much more quickly than any of us could have anticipated when we started this research,” Dr. Robinson said. “Ideas that once may have seemed unattainable—like a hand-held, stall-side testing device—are now coming into sight as real and tangible possibilities. We just need continued support to help get us there.” MeV This study is supported in part by the Pennsylvania Horse Breeders Association, the Pennsylvania State Horse Racing Commission, the University of Pennsylvania McCabe Fund and New Bolton Center’s Raymond Firestone Trust Research Grant.
For more information: You Y, Proctor RM, Guo K, et al. Use of high resolution/accurate mass full scan/data-dependent acquisition for targeted/non-targeted screening in equine doping control. Anal Methods. 2021 Apr 7;13(13):1565-1575. https://pubmed.ncbi.nlm.nih.gov/33710179/ Haughan J, Jiang Z, Stefanovski D, et al. Detection of intra-articular gene therapy in horses using quantitative real time PCR in synovial fluid and plasma. Drug Test Anal. 2020 Jun;12(6):743-751. https://pubmed.ncbi.nlm.nih.gov/32133745/ Guan F, Fay S, Li X, et al. Identification of ex vivo catabolites of peptides with doping potential in equine plasma by HILIC-HRMS. Drug Test Anal. 2020 Jun;12(6):771-784. https://pubmed.ncbi.nlm.nih.gov/32100400/ ModernEquineVet.com | Issue 5/2021
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INFECTIOUS DISEASES
Macrolide/Rifampin Prophylaxis for R. equi Leading to Multidrug Resistance By Adam Marcus The overuse of macrolide/rifampin for prophylactic therapy to treat foals infected with Rhodococcus equi has led to the emergence of antibiotic-resistant forms of the bacteria that could pose a threat to other farm animals and even people, researchers have found. The growing spread of macrolide/rifampin-resistant R. equi, first detected in 2002 in Kentucky, has been linked to a clone of the microbe, named R. equi 2287, which relies on a chromosomal mutation to evade rifampin and a set of resistance genes that protects bacteria against macrolides, lincosamides, streptogramins, tetracycline and sulfamethoxazole. A new resistant clone, labeled G2016—for the year it was first discovered—suggests that the problem may be getting worse. “The use of prophylactic chemotherapy and the treatment of subclinically pneumonic foals with antibiotics represents a clear example of antimicrobial overuse that is driving the selection of multidrug resistant bacteria, including R. equi, in the animals and the environment,” said Sonsiray Álvarez-Narváez, DVM, of the Athens Veterinary Diagnostic Laboratory at the University of Georgia College of Veterinary Medicine, who led the new study. “An increase of resistant bacteria in the farm environment directly translates into an increase in the chances of a foal being exposed and potentially ill by resistant bacteria, whose infections are more challenging to treat and have a worse prognosis.” For the study, Dr. Álvarez-Narváez and her colleagues performed genetic analyses of samples of R. equi from foals being raised in Florida, Kentucky, Louisiana, New York and Texas between 2002 and 2017. Of the samples, 38 were resistant to a macrolide and rifampin, 8 were resistant to macrolides only and 24 were susceptible to the drugs.
In addition to finding samples of the 2287 clone of the bacteria, which has the same core genome as the typical MaR resistant strain, they also found the new resistant clone, G2016. As with the 2287 clone, this one has a chromosomal mutation to evade rifampin and gained its multidrug resistance to the other antimicrobials by acquiring a plasmid, or ring of DNA, called pRErm46. According to Dr. ÁlvarezNarváez, that meant 2 things: “Up to 2015, pRErm46 was not transferred to other genotypes, and dissemination of macrolide and rifampin resistance in R. equi across the U.S. was caused by the same bacteria [clone 2287] that passed from 1 animal to another.” How clone 2287 emerged is still a mystery, she said. “But once it did, the action of the 2 antibiotics made it easy for these resistant bacteria to take over, because most competition was killed by the action of the dual antibiotic combination,” Dr. Álvarez-Narváez told Modern Equine Vet. “This way, dual therapy makes it more difficult for resistant bacteria to emerge but once they do, clonal populations carrying the key resistance elements are favored.” Dr. Álvarez-Narváez said the findings, and similar studies, offer a clear message to equine veterinarians: “They should stop using antibiotics prophylactically or to treat foals with subclinical R. equi pneumonia with antimicrobials because there are several studies showing that, in many cases, foals presenting subclinical lung lesions recover spontaneously without the help of chemotherapy. “I understand that in many cases clinicians are under a lot of pressure from breeders and owners to treat the animal, but they should minimize the use of antimicrobials to strictly necessary cases because by trying to assist the foals with subclinical pneumonia, they may be creating a larger problem of antimicrobial resistance.” MeV
Prophylaxis of subclinically pneumonic foals is a clear example of antimicrobial overuse that leads to resistance.
For more information: Álvarez-Narváez S, Giuère S, Cohen N, et al. Spread of multidrug-resistant Rhodococcus equi, United States. Emerg Infect Dis. 2021;27(2):529-537. https://doi.org/10.3201/eid2702.203030 (https://wwwnc.cdc.gov/eid/article/27/2/20-3030_article) 14
Issue 5/2021 | ModernEquineVet.com
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NEWSNOTE
Tackling the Heat of the Tokyo Olympics
Images: credit Christopher Elliott
The Tokyo Olympics, which were delayed by COVID19, will take place in the heat and humidity of the Japanese summer, in temperatures likely to reach more than 105° F. To help involved veterinarians keep equine athletes safe in such heat, the Equine Veterinary Journal is giving free-to-read access to articles covering the health and welfare of horses competing in hot and humid conditions. The Special Collection Preparing for Tokyo Olympics contains 11 highly relevant papers together with a comprehensive editorial forward from Christopher Elliott. “This is not the first time that extreme heat and humidity has challenged the viability of Equestrian events at the Olympic Games,” said Christopher Elliott, DVM, DACVSMR. “It is vital that we learn from the past to ensure the welfare of equine athletes in the future.” The special collection highlights the ground-
breaking research, which followed the 1992 Barcelona Olympics. “This work revolutionized our understanding of managing equine athletes in hot and humid conditions,” Dr. Christopher said. “It optimized identification and management of heat stress and allowed practical solutions to cooling methods to be established, enabling the successful running of the 1996 Atlanta Olympics.” Leading up to the 2008 Beijing Olympics, another concerted effort by veterinary researchers further advanced understanding, and it is on the back of this work that recent literature about equine heat stress and optimized cooling methods has been established. The special collection explores: • Physiological, metabolic and biochemical responses of horses competing in the speed and endurance phase of a 3-day event • Physiological responses to the endurance test of a 3-day-event during hot and cool weather • Physiological responses of horses competing at a modified 1-Star, 3-day event • Adaptations to daily exercise in hot and humid ambient conditions in trained Thoroughbred horses • Sweating rate and sweat composition during exercise and recovery in ambient heat and humidity • Physiological responses of horses to a treadmillsimulated speed and endurance test in high heat and humidity before and after humid heat acclimation • Comparison between 2 post-exercise cooling methods • Contributions of equine exercise physiology research to the success of the 1996 Equestrian Olympic Games: a review • An index of the environmental thermal load imposed on exercising horses and riders by hot weather conditions • Use of the Wet Bulb Globe Temperature (WBGT) Index to quantify environmental heat loads during 3-day-event competitions • Risk factors for exertional heat illness in Thoroughbred racehorses in flat races in Japan (2005–2016)
For more information: Access the collection here. https://beva.onlinelibrary.wiley.com/hub/journal/20423306/homepage/sc_olympics 16
Issue 5/2021 | ModernEquineVet.com
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