Strangles is a highly contagious respiratory disease in horses caused by the bacterium Streptococcus equi subspecies equi. Horses of all ages can be affected by the infection, but younger horses are especially vulnerable. Although the mortality rate for strangles is low, the disease can develop into more complicated problems if untreated. In rare cases, the infection may spread to other parts of the body, affecting major organs.
“Know the signs,” said Semira Mancill, DVM, DACT, Texas A&M Veterinary Medical Diagnostic Laboratory, TVMDL, veterinary diagnostician. “Horses may be contagious even before showing signs, so early detection is key.”
Symptoms of strangles include fever, a thick nasal discharge, difficulty swallowing, swelling and abscesses under the jaw. The disease is called strangles because the swelling can obstruct a horse’s airway, which causes difficulty breathing. Usually, infected horses will feel sick for a few weeks, experiencing respiratory issues and discomfort.
Recovering from strangles
Strangles spreads through direct contact with infected horses. The disease can also be transmitted indirectly through contact with surfaces contaminated with Streptococcus equi equi. Barn equipment including feed and water buckets are commonly found to contain infectious agents. Human hands and clothing may also harbor the bacterium.
Since strangles is highly contagious, strict isolation is the first step in preventing further outbreaks. Horses that are infected or suspected of being infected should immediately be isolated from others. Infected horses should not be taken to public events, and no horses should enter the contaminated facility.
Some horses may still carry bacteria without showing symptoms. These are called asymptomatic carriers.
“Horses that have had strangles should be tested several weeks after symptoms resolve to confirm that they are no longer shedding bacteria,” Mancill said. “Carrier horses can be a hidden source of infection, so this step is essential for disease control.”
After an outbreak is discovered, the facility should be thoroughly cleaned. All organic material should be removed from surfaces. Caregivers should disinfect all water buckets, troughs, feeders, fences, stalls, tack and trailers with a diluted bleach solution. The materials cleaned using bleach should have plenty of time to dry before they are used again.
Testing options
TVMDL performs PCR tests and bacterial cultures to detect strangles. A positive result from a PCR test indicates that the DNA of Streptococcus equi equi is present, meaning the horse is likely infected or a carrier. This specific and sensitive test option provides quick results in a day or two. The PCR test differentiates between Streptococcus equi subspecies equi and Streptococcus equi subspecies zooepidemicus, which are two closely related bacteria.
As an alternative, results from bacterial culture take longer, but a positive result confirms the presence of live bacteria. In this case, it is certain the horse is shedding the infectious material. This method is useful for determining whether the bacteria are actively replicating.
Key takeaways on strangles management
Preventing and managing strangles requires isolating infected horses, limiting horse movement in and out of the facility and disinfecting surroundings. Communication with your veterinarian and testing are also essential to detect and control the disease early. These measures are key to reducing the risk of further outbreaks and protecting equine health.
For more information on TVMDL’s testing options visit tvmdl.tamu.edu or call the College Station laboratory at 1.888.646.5623 or the Canyon laboratory at 1.888.646.5624.
