Disease Du Jour: Equine Strangles

Amy Dragoo

In Episode 78 of the Disease Du Jour podcast, Ashley Boyle, DVM, DACVIM, talks about equine strangles. She is an Associate Professor of Medicine, Section of Field Service, at the University of Pennsylvania’s New Bolton Center. She received her DVM from Cornell University and was boarded in internal medicine at UC Davis. Her research interests center around equine infectious disease, especially equine strangles and vaccination.

Why is equine strangles such an issue in the equine population? “It is a highly contagious disease that is easily spread and often the carriers are silent,” explained Boyle. “The bacteria live a long time, with the ambient temperature and moisture content depending on how long they stick around.”

Fomites are useful to the strangles causative bacteria Streptococcus equi subspecies equi (also known as S. equi). Fomites can include a shared water source, water buckets, tack and even people.

She said when testing for equine strangles, she prefers PCR over culture. “You can miss some animals with culture,” she said. 

She cautions that if a horse tests negative on culture and is released into a population, it might end up spreading the bacteria. That happened in a research situation that was published on.

Boyle said if you want to use culture, use more than one sample. “If you think a horse has strangles and it tests negative, test again,” she advised. “Horses don’t shed up to 48 hours after a fever.”

She also advised veterinarians to look for carriers after an outbreak using both nasopharyngeal swabs and guttural pouch washes. “With a gutter pouch wash, you are 50% more likely to find positives,” Boyle noted.

Boyle stressed the importance of isolating horses that are showing clinical signs, fever or have been exposed. She also reminded that young horses or older horses might not have been exposed, or that some older horses have waining immunity or a less-competent immune system.

Other topics discussed:

  • bastard strangles
  • management of a boarding stable
  • vaccines
  • use of antibiotics


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