Researchers: Better Way to Diagnose Strangles in Horses Foal showing signs of swelling from strangles. Photo © 2015

Researchers: Better Way to Diagnose Strangles in Horses

Researchers say they have identified a better method for diagnosing strangles in horses. Strangles is a highly contagious, upper respiratory disease that affects horses, donkeys and mules.
Research by Dr. Ashley Boyle of New Bolton Center’s Equine Field Service team shows the best method for diagnosing strangles in horses is to take samples from a horse’s guttural pouch. For horse owners, the guttural pouch is one of a pair of air chambers in the neck, just behind the skull and below the ears. The samples are analyzed using a loop-mediated amplification (LAMP) polymerase chain reaction (PCR) test.
PCR is a molecular diagnostic test to find DNA within a sample through amplification that uses heat. LAMP is a type of DNA amplification that does not use heat, but rather travels in a loop.
strangles draining guttural pouch
Strangles is caused by Streptococcus equi bacteria. Symptoms include nasal discharge, lethargy, and very high fever (over 103 degrees) in horses. The lymph nodes can swell to the point of cutting off the airway, thus the name strangles.

If the infected lymph nodes break open in the throat, puss can collect in the guttural pouch, which is an air-filled structure within the horse’s head that arises from the Eustachian tube on each side. Dr. Boyle states once in the guttural pouch, the bacteria can be difficult to eradicate.

Typically it takes two months to clear up an outbreak, according to Dr. Boyle, and it can easily last for four months.

Dr. Boyle says her goal is to significantly reduce the time, effort, and expense required to test horses for strangles.

The current testing recommendation for strangles is 10 years old and labor intensive. Vets have to get a wash of the throat and obtain negative tests three times, each a week apart, to safely declare a horse clear of the infection.

Until a barn is cleared, horses suspected of infection must be quarantined, and bio-security protocols should be followed to prevent the spread of the disease. Doing so can prove expensive and inconvenient for horse owners.

“We are working to avoid going to farms three separate times in three separate weeks,” said Dr. Boyle, who is an assistant professor and board-certified clinician in Internal Medicine.
“It is important to determine which horses are carriers, which horses are not carriers, and which horses have come in contact with the bacteria and are immune, but have become carriers,” Dr. Boyle said. “Our recommendation is to go into the guttural pouch for the sample to determine if they are carriers.”
Dr. Boyle presented the abstract of her research earlier this year, titled “Determining Optimal Sampling Site for Streptococcus equi Subspecies Equine Carriers Using a Loop-Mediated Isothermal PCR Assay,” at the Havemeyer Foundation workshop on streptococcal disease in Denmark. She also presented at the American College of Veterinary Internal Medicine Conference in Indianapolis.
Dr. Boyle is working toward a highly accurate stall-side test for diagnosing strangles in horses.