Biosecurity gaps, early fever detection and new technologies could help prevent future shutdowns
Courtesy of Merck Animal Health
RAHWAY, N.J., March 11, 2026 – When equine herpesvirus-1 (EHV-1) swept through a Texas barrel racing event in November 2025, the consequences extended well beyond the horses involved. As events were canceled across disciplines and horses were quarantined, the outbreak swiftly demonstrated how a single biosecurity breach can affect an entire competition season.
With horse travel and events ramping up again in 2026, equine health experts are urging owners and organizers to apply the lessons of last year as the new season gets underway.
Lesson 1: Fever detection is paramount
With EHV-1, fever typically appears before nasal shedding begins. This makes early detection both possible and critical. As soon as fever is noted, an affected horse can be isolated before it begins shedding virus, shrinking the circle of exposure. It’s a narrow window of time, but one that’s actionable.
According to Katie Flynn, BVMS, MRCVS, senior staff veterinarian for equine health and biosecurity with the United States Equestrian Federation and an expert in equine biosecurity, acting within that window is not optional. “Biosecurity protocols that include isolating horses at the first detection of fever and monitoring clinical signs can help reduce transmission, lower disease risks and sustain business operations,” Flynn says.
Flynn recommends monitoring horses’ temperatures twice daily throughout an event and immediately reporting any reading above 101.5°F to a veterinarian.
Lesson 2: Speedy identification saves critical time
In an active outbreak, the speed at which organizers can identify infected, exposed and at-risk horses determines how quickly they can contain the spread. Paper records and visual identification methods slow down the process exactly when speed matters most.
Flynn points to microchip technology as a more reliable alternative. Standard microchips provide a tamper-proof, instantly scannable form of identification that allows state animal health authorities to efficiently trace both infected horses and those that may have been exposed. For events with large or rotating populations of horses, that traceability can accelerate response to an outbreak.
Temperature-sensing microchips extend that capability even further. For example, the Bio-Thermo® Microchip from Merck Animal Health combines identification with passive health monitoring, logging body temperature data each time a horse is scanned and flagging elevated readings. Flynn notes that this kind of ongoing temperature monitoring can serve as an early warning mechanism, catching subtle changes in an individual horse’s baseline before clinical signs become obvious.
Lesson 3: Create isolation plans before the first fever
One of the most common biosecurity vulnerabilities at equine events is the absence of a plan for managing a suspect case. By the time a sick horse is identified, it’s too late to begin designating isolation space or sorting out reporting protocols.
Flynn recommends that event organizers designate isolation areas in advance and create mandatory reporting protocols requiring a veterinarian to be notified at the first sign of fever or clinical illness. On the participant side, horse owners should make sure vaccination status is current before they arrive. They should be guided by vaccination guidelines from the American Association of Equine Practitioners (AAEP), applicable organization and show rules, and their own veterinarians. Before the event, organizers should also require recent health certificates and evidence of EHV-1 and influenza vaccination within the previous six months for all participating horses.
Lesson 4: Events are vulnerable ecosystems where biosecurity should be implemented rigorously
The conditions that make equine events what they are—large numbers of horses from different regions, close housing, shared spaces and equipment, and high volumes of human traffic—are the same conditions that make disease transmission easier. Increased interstate and international movement of competition horses compounds the risk.
Flynn identifies five biosecurity measures that should be non-negotiable at every event:
- Limit direct contact between horses.
- Restrict human-to-horse interaction to essential personnel only.
- Avoid communal water sources.
- Do not share equipment unless it has been thoroughly cleaned and disinfected between uses.
- Monitor horses’ temperatures twice daily and immediately report readings above 101.5°F to a veterinarian.
Flynn frames the challenge as one the equine industry can meet, but only through deliberate partnership between owners, event organizers and veterinarians. “The primary objective remains the same,” she said: “only healthy horses enter each venue, maintain their health throughout, and return home safely.”
Tracking threats through biosurveillance
Proper disease management begins with understanding what’s infecting horses. The Merck Animal Health Equine Respiratory Biosurveillance Program has tracked respiratory pathogens across the United States for 18 years. In partnership with the PCR Laboratory at University of California, Davis, School of Veterinary Medicine, the program delivers rapid test results, enabling prompt treatment decisions and helping curb further disease spread (see Figure 1).
The monthly cumulative depicts the seasonal effect of respiratory pathogens spanning 18 years of surveillance. EHV-4 continues to be more prevalent in the fall months, in contrast to the other respiratory pathogens (especially EIV) that are more prevalent in the winter and spring months.
“The surveillance data we’ve gathered over 18 years gives veterinarians and horse owners a clearer picture of what’s circulating and when,” says Duane Chappell, DVM, Associate Director for Equine Pharmacovigilance and Veterinary Professional Services at Merck Animal Health. “The goal is to give them the information they need to act early, not just respond after the fact.”
Horse owners are urged to talk to their veterinarian about individualized vaccination recommendations and biosecurity planning before attending events this season. Get more EHV-1 facts, and learn more about the Equine Respiratory Biosurveillance Program and regional disease threats with the equine disease outbreak map.
¹ Merck Animal Health and University of California, Davis (Nicola Pusterla). Infectious Upper Respiratory Disease Surveillance Program. Ongoing research 2008–present.
About Merck Animal Health
At Merck, known as MSD outside of the United States and Canada, we are unified around our purpose: We use the power of leading-edge science to save and improve lives around the world. For more than a century, we’ve been at the forefront of research, bringing forward medicines, vaccines and innovative health solutions for the world’s most challenging diseases. Merck Animal Health, a division of Merck & Co., Inc., Rahway, N.J., USA, is the global animal health business of Merck. Through its commitment to The Science of Healthier Animals®, Merck Animal Health offers veterinarians, farmers, producers, pet owners and governments one of the widest ranges of veterinary pharmaceuticals, vaccines and health management solutions and services as well as an extensive suite of connected technology that includes identification, traceability and monitoring products. Merck Animal Health is dedicated to preserving and improving the health, well-being and performance of animals and the people who care for them. It invests extensively in dynamic and comprehensive R&D resources and a modern, global supply chain. Merck Animal Health is present in more than 50 countries, while its products are available in some 150 markets. For more information, visit www.merck-animal-health.com and connect with us on LinkedIn, Facebook, X (formerly Twitter) and Instagram.
