Strangles in Horses: Interpreting Gold-Standard Test Results

Researchers found that while any of the three tested qPCR diagnostic approaches can be effective in diagnosing true strangles cases, one stood out.

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strangles in horses
Strangles can spread through horse barns with ease. Thus, it’s important that veterinarians diagnose it quickly and accurately to prevent outbreaks. | Photo: Courtesy Animal Health Trust

An infectious respiratory disease caused by Streptococcus equi subspecies equi bacteria, strangles in horses spreads with ease. Thus, it’s important that veterinarians diagnose it quickly and accurately to prevent outbreaks. They have two methods of doing so: culture and the more reliable qPCR test, which detects bacterial and viral DNA.

Nicola Pusterla, DVM, PhD, Dipl. ACVIM, professor of medicine and epidemiology at the University of California, Davis, School of Veterinary Medicine, reviewed these methods and their efficacy at the 2018 American Association of Equine Practitioners Convention, held Dec. 1-5 in San Francisco, California.

In recent years, he said, qPCR has supplanted traditional S. equi culture as the gold-standard diagnostic test for strangles in horses. While culture is convenient and cost-effective, it’s time-consuming and can produce false negatives. The qPCR test is much faster, with better sensitivity and specificity (ability to accurately identify results). The results, however, can be difficult to interpret, said Pusterla, as veterinarians often can’t determine whether it has detected a dead—indicating past exposure or infection—or live organism

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Alexandra Beckstett, a native of Houston, Texas, is a lifelong horse owner who has shown successfully on the national hunter/jumper circuit and dabbled in hunter breeding. After graduating from Duke University, she joined Blood-Horse Publications as assistant editor of its book division, Eclipse Press, before joining The Horse. She was the managing editor of The Horse for nearly 14 years and is now editorial director of EquiManagement and My New Horse, sister publications of The Horse.

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