How and Why is Strangles So Contagious in Horses?

How and Why is Strangles So Contagious in Horses?

It can spread through touching or sharing tack, clothing, sharing hay or grain, and even touching other animals like dogs and cats.

This article first appeared in the March 2018 issue of Heels Down Magazine. For more stories worth reading, subscribe now in the app and get a new issue delivered every month.


When a Strangles outbreak this winter forced three equestrian facilities into quarantine in a suburban county outside of Tampa Bay, Fla., horse owners were aflutter with worry about the highly contagious, and often gross display of the infection in horses.

Four horses began to show signs of the disease after a haul-away trail ride in a neighboring county’s state park system. Those symptoms eventually spread to other horses at their home barns. By protocol, farms remain under quarantine until the horses who have been exposed to the bacterial infection no longer display the symptoms nor test positive for the disease, according to the Equine Disease Communication Center.

Strangles is most commonly characterized as a bacteria that infects the upper airway and lymph nodes of a horse’s head and neck. It’s one of the most commonly diagnosed contagious diseases in horses across the globe. What makes it so contagious is that the bacteria can survive in waterborne areas, like buckets and troughs, for more than a month. It can spread through touching or sharing tack, clothing, sharing hay or grain, and even touching other animals like dogs and cats. Horses can also physically “shed” the bacteria to other horses for months, or even years, after being infected and no longer displaying symptoms.

Horses that have contracted Strangles have extensive swelling and sometimes ruptured lymph nodes which produces a thick and creamy mucus-like pus visible in the nostrils, according to the Ontario Ministry of Agriculture, Food, and Rural Affairs. Fever, depression and loss of appetite are routinely associated with it.

Diagnosis can be tricky, too, because not all infected horses display sickness symptoms, said Dr. Amanda House, a veterinarian and clinical associate professor with the University of Florida.

“Horses need to have diagnostic screening to identify asymptomatic carriers, and it can be a challenge,” she said. “Typically, we would recommend screening horses with a nasopharyngeal wash, a guttural pouch lavage, and endoscopy and lavage. The samples are submitted for specific strep equi (the name of the bacteria that causes the infection) testing.”

The number of Strangles outbreaks in Florida is just 40 for the entire 2017 year. Because of how contagious it can be, Strangles is not limited to any geographical area and can be contracted anywhere around the world. For comparison, the United Kingdom sees an average of 600 cases a year, according to the Animal Health Trust.

Most cases recover completely without long term adverse effects.

The UK-based Animal Health Trust, a veterinary and scientific research charity, is partnering with the Houston Methodist Research Institute to study how genes linked to a sore throat infection in humans can help veterinarians better understand the genes that cause the Strangles infection in horses.

While there is a common vaccine administered to horses for Strangles, it does not guarantee prevention, Dr. House said.

“Vaccination may lessen the severity or course of the disease,” Dr. House explains. “Most cases recover completely without long term adverse effects.”

Some horses may require antibiotics for complicated infections, she said, but most routine cases do not need it.

A quick recovery truly depends on responsible horse and barn owners. Isolating horses during the onset of an outbreak is essential.

“One of the best ways to identify horses that may become clinical is taking temperatures,” Dr. House said. “Taking temperatures twice a day and isolating horses at the first sign of fever can help stop the spread of the disease.”

Where To Track Equine Disease Outbreaks:
You can track and search for outbreaks at the Equine Disease Communication Center by state at equinediseasecc.org/alerts/outbreaks.

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