What is strangles?

Strangles is a highly contagious disease affecting horses and other equids caused by a bacteria.

What are the clinical signs of strangles?

Clinical signs of strangles can include fever, lethargy, nasal discharge, soft cough, reluctance to eat or drink, abnormal head positioning, and swelling and abscessation of lymph nodes. (1) The abscessed lymph nodes can become enlarged, hard and painful and can block the airways of the horse (hence the name strangles). (2) Abscesses usually rupture 1-4 weeks after infection. A small percentage of horses can develop a more serious illness, but most horses recover well. Strangles can occur in all ages of horses, but typically younger horses have more severe clinical disease.

Are there any human health risks?

(2)  Human infection is rarely a concern but has occurred in immunocompromised individuals.

How is strangles transmitted?

Infected horses shed strangles through discharge from the lymph nodes, nose, and eyes. (3) Strangles can be spread both directly, through nose-to-nose contact, and indirectly, through contact with a contaminated environment. Routes of indirect transmission include sharing of water, food, housing, tack, etc. Flies are another route of indirect transmission. Animals shedding bacteria may appear healthy, and animals that have recovered from strangles may continue to shed bacteria for several weeks.

How is strangles diagnosed and treated?

Strangles is diagnosed using clinical signs and laboratory testing. (2) Most cases require only supportive care.

Prevention and control of strangles

The best way to prevent strangles in horses is by limiting their exposure. (2) Quarantine and screening of new horses, cleaning and disinfection of potentially contaminated housing and equipment, and education of people handling the horses are important ways to prevent strangles outbreaks. (3) Strangles vaccines are available but have limited efficacy and should be discussed with a veterinarian.

For more information

OMAFRA fact sheet
Equine Strangles - UK
ACVIM consensus statement


  1. Ogilvie TH. Large animal internal medicine. Baltimore, MD: Williams & Wilkins; 1998.
  2. Boyle AG, Timoney JF, Newton JR et al. Streptococcus equi Infections in Horses: Guidelines for Treatment, Control, and Prevention of Strangles—Revised Consensus Statement. J Vet Intern Med 2018; 32(2): 633-647.
  3. Rush RB. Strangles in Horses - Respiratory System. Merck Veterinary Manual. Accessed May 18, 2018
Published date: 
March 3, 2021

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