The Veterinary Corner series, brought to you by Merck Animal Health, features insights from leading veterinarians on some of the most pressing health issues affecting horses today.
By Bryant Craig, DVM
As the leaves begin to change and the air turns crisp, it’s important to recognize that while fall brings an increased risk of common respiratory diseases like equine herpesvirus type 4 (EHV-4) and equine influenza, it’s also a prime time for less recognized threats such as rabies and equine protozoal myeloencephalitis (EPM). Be prepared by working with your veterinarian to help prevent disease and catch any issues early.
Rabies. 100% Fatal. Always Preventable.
When people ask me about the need for rabies vaccination, I’m transported back to when I was 8 or 9 years old. My pony, Dolly, wasn’t acting herself, so the veterinarian came to check her.
The next day, Dolly passed away. The vet tested her body for rabies and found she’d been positive.
We’d all handled Dolly the day before, which meant we’d been exposed to rabies. Everyone had to get immune globulin shots to try to prevent infection. Luckily, the shots worked and none of us became ill.
Rabies is one of the deadliest diseases a horse can contract, with nearly a 100% fatality rate once symptoms appear. Fortunately, it’s also entirely preventable with proper vaccination. Even though rabies cases in horses are relatively rare, they do occur every year. Three equine rabies cases have already been reported this year,[1], [2] highlighting the ongoing risk.
There’s always the significant and serious potential for any infected animal to transmit the disease to humans, which carries important public health consequences. That’s why the American Association of Equine Practitioners (AAEP) recommends every horse be vaccinated every year.[3] While rabies can occur any time of the year, cases in horses tend to increase in early fall, likely due to increased interaction between horses and wildlife reservoirs of the rabies virus, such as bats, raccoons, skunks and foxes, which are more active during these times. Horses are naturally curious animals, often exploring their surroundings with their noses, and a nip on the muzzle or limb could be disastrous. Since wildlife may enter barns (especially at night), both stalled horses and horses on pasture have the potential to be exposed.
Even if you don’t think rabies is a concern in your area, it’s crucial to vaccinate your horse annually. Ask your veterinarian about PRESTIGE® EquiRab®, the first rabies vaccine developed specifically for the horse and trusted for exceptional safety.
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Increased EPM Risk
Equine protozoal myeloencephalitis is another serious disease that tends to spike in the fall.[4] The reason? Opossums, which are the primary hosts of the parasites that cause EPM, become more active as the weather cools. This increased activity means a higher chance of your horse being exposed to these parasites, usually through contaminated feed or water. Autumn is also a time when months of heavy exercise, transport and other stressful events for horses can take a toll, which can increase horses’ risk of EPM.
EPM can lead to severe neurological issues in horses, including incoordination, muscle weakness, and even seizures. If you notice any signs of EPM, such as stumbling or unusual behavior, it’s important to contact your veterinarian immediately. Early diagnosis and treatment are critical to your horse’s recovery.
After diagnosing EPM, your veterinarian may recommend an FDA-approved treatment product like PROTAZIL® (1.56% diclazuril) Antiprotozoal Pellets. Horses treated with an anticoccidial drug like PROTAZIL® are 10 times more likely to improve than untreated horses.4 PROTAZIL® is the only FDA-approved product that comes in a convenient top-dress formula administered on the daily feed ration. See full prescribing information.
To reduce the risk of EPM, keep your barn and surrounding areas clean and free of food or waste that might attract opossums. While it’s nearly impossible to eliminate all risks, maintaining a clean environment is a good first line of defense.
Fall Vaccination and Biosecurity Tips
Infectious diseases including equine flu and EHV-4 ramp up in the fall and winter months. EHV-4 occurs most frequently in October, while equine flu season extends from December through May.[5] These diseases can spread quickly, especially in barn environments or during travel for competitions.
Make sure your horse’s vaccinations are current. A booster shot this fall may be necessary to protect your horse throughout the winter and into spring. Beyond vaccinations, it’s important to practice good biosecurity. This includes monitoring your horse’s temperature regularly while traveling, quarantining new horses before they join your herd, and avoiding sharing communal equipment and water sources.
Final Thoughts
Fall is a great time for all things horse. By staying vigilant and proactive—ensuring vaccinations are current and practicing good barn hygiene—you can help your horse navigate the season safely and keep them performing at their best.
For more information on these important fall health topics and more, visit Merck Animal Health Equine.
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IMPORTANT SAFETY INFORMATION: PROTAZIL® is contraindicated in horses with known hypersensitivity to diclazuril. The safety of Protazil in horses used for breeding purposes, during pregnancy, or in lactating mares, and use with concomitant therapies in horses has not been evaluated. Do not use in horses intended for human consumption. Not for human use. For complete safety information, refer to the product label.
ABOUT THE AUTHOR
Bryant Craig, DVM, is associate director of scientific affairs for equine professional services and pharmacovigilance at Merck Animal Health. Prior to joining Merck Animal Health, Dr. Craig owned and operated a private equine veterinary practice for six years in central Oklahoma before joining a top Quarter Horse ranch as resident veterinarian.
[1] Equine Disease Communication Center https://www.equinediseasecc.org/rabies
[2] South Carolina Dept of Public Health https://dph.sc.gov/news/two-rabid-foxes-confirmed-separate-cases-newberry-and-florence-counties-and-rabid-horse
[3] AAEP Vaccination Guidelines (aaep.org/guidelines/vaccination-guidelines/core-vaccination-guidelines/rabies)
[4] 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.
[5] Merck Animal Health and University of California, Davis, School of Veterinary Medicine (Nicola Pusterla). Infectious Upper Respiratory Disease Surveillance Program. Ongoing research 2008-present
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