By Lori Larson and Dr. Alisha Bretz, DVM (first published in the July 2025 issue of The Equiery)

In the quiet countryside of Montgomery County, the serenity of Wyndham Oaks was disrupted in early April by an unexpected health event. An outbreak of strangles—an infectious bacterial disease affecting horses—led to the immediate quarantine of the barn, requiring horse owners, trainers, and local veterinarians to respond with patience, thoughtfulness and diligence. We share our story in hopes that the entire equine community will benefit from our experience.

The Silent Threat of Hidden Carriers

Strangles, caused by the bacterium Streptococcus equi, spreads through direct contact or contaminated surfaces. Except in the young, low body condition or immunocompromised horses, the symptoms, if present, are fever and nasal discharge. Vaccinations will not always prevent a horse from getting Strangles; but can shorten the duration of and reduce the severity of symptoms. More severe cases include swollen lymph nodes that can abscess and rupture.

One of the biggest challenges in containing strangles is that some horses can carry and shed the bacteria without ever showing symptoms. In fact, some studies suggest that up to 8% of horses can remain as carriers even when showing no signs of infection. These asymptomatic carriers, often referred to as “silent shedders,” can unknowingly spread the disease to other horses.

“Strangles isn’t always obvious,” explained Dr. Bretz. “Some horses appear perfectly fine but can still transmit the infection. That’s why full-barn testing is absolutely crucial in stopping its spread. If any asymptomatic carriers aren’t identified, they cannot be treated to ensure they don’t spread in the future.”

Lockdown Measures and Total Testing

In a swift and necessary move, Wyndham Oaks restricted all movement in and out of the barn. Biosecurity measures were heightened, including disinfecting stalls, isolating obviously infected horses, taking temperatures of all horses twice daily and enforcing strict protocols for caretakers.

Determined to control the potential outbreak as efficiently as possible, barn management, alongside the boarder community, committed to testing every single horse on the property, an incredible undertaking when approximately 80 horses are involved. This all-encompassing approach ensured early detection, guiding treatment efforts and preventing any further spread of the disease.

The Gold Standard of Testing

The gold standard for detecting strangles is currently polymerase chain reaction (PCR) tests and bacterial cultures, both of which help identify carriers and active infections. PCR testing is highly sensitive and can detect even small amounts of Streptococcus equi DNA, making it one of the most reliable methods for ensuring a disease-free barn. The best sampling method involves passing an endoscope into the horse’s guttural pouches and introducing 60ml of saline.  The sample then runs out of the pouches and down through the pharynx and nasal passages to effectively test the entire area. This ensures bacterial DNA is picked up from pouches, pharynx, or nostril.  It is the best way to be sure what you are dealing with and, if mucus is present in the pouches, a simple procedure can clear the space of mucus (and possible infection) at the same time. Otherwise, a nasopharyngeal wash is more reliable than either a swab or blood test but it can miss asymptomatic carriers and needs to be repeated up to 3 times before a horse is officially deemed negative.  These samples are also able to be tested for a whole panel of infectious respiratory pathogens not just strangles, all performed by PCR. 

The blood test for Strangles, called an M protein, detects antibodies specific to Strangles but not the Strangles bacteria itself, making it a much less reliable testing method especially in acute infection.

To show the impact of asymptomatic carriers, out of 79 horses tested, we identified 4 positive horses. There were likely more positive horses but thanks to their vaccine induced and natural immunity they cleared it quickly after only 24 hours of minor symptoms and tested negative when whole barn testing was performed. Only two that tested positive showed outward symptoms of any kind, yet the other two could still silently spread the infection. By identifying these horses and using basic biosecurity measures and treatment, we were able to clear the barn of any infection, and the quarantine, in a miraculous (and the minimum) three weeks!

The Emotional Toll

For many horse owners, the quarantine was a tense period of uncertainty and frustration. Outside plans with their horses had to be put on hold. Those that use social media as their guide to Strangles were particularly scared, given the inaccurate and incomplete info published there. Barn management made a point of extensive, fact-based communications with the boarders so they could understand what was and would happen. “It was an anxious time, but the testing gave us clarity, and management staff communicated every detail,” shared Jane Thery, a long-time boarder. “Knowing that every horse was monitored daily reassured us that we were doing everything possible to get through this safely and quickly.”

Despite the challenges, with a commitment to 100% testing, the community came together in a powerful display of resilience and care for each other. Questions went from, “Who brought this here?“ (an impossible and unimportant question to answer) to, “What can we do to prevent exposure when we are away from the barn?”. Barn staff and the Monocacy Equine veterinarians worked tirelessly to oversee testing and containment. Education became a priority, ensuring that owners understand what a Strangles outbreak realistically looks like and how to prevent future outbreaks.

A Swift but Thorough Resolution

Thanks to the commitment of Wyndham Oaks’s boarders, management, and veterinary professionals, the entire event (from initial symptoms to the end of quarantine) was over in a month. The comprehensive testing, treatment and containment strategy allowed for precise recovery timelines, making it possible to confirm that there was no spread. All horses were free from infection before resuming normal operations.

The experience serves as a reminder of how quickly an outbreak can disrupt our world. Neither large nor small farms are exempted from the possibility of a Strangles outbreak when horses come and go from the property.  Our experience reminds us to recommit to heightened infection prevention practices when we take our horses off the farm. But more than anything, it stands as proof that when a boarder community pulls together, even the most difficult challenges can be overcome.