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What is Strangles?

Strangles in horses is a respiratory bacterial infection caused by Streptococcus equi. Strangles (sometimes also called “distemper”) gets its name from its characteristic symptom of enlarged lymph nodes surrounding the upper airways, which can cause horses to suffocate.

Strangles is one of the most commonly diagnosed equine infectious diseases worldwide, and it remains widespread today.

Loss of appetite is a sign of Strangles

What horses are at risk?

Young horses (weanlings and yearlings) are commonly affected by Strangles, but horses of any age can be infected. The primary risk factor for Strangles is being in close proximity with horses whose medical history you are unfamiliar with.

How is Strangles in horses contracted?

Between horses via nasal discharge

Strangles is highly contagious and is transmitted directly between horses via the nasal discharge of an infected horse. Horses can shed the bacterium for months or even years without showing signs or symptoms, while still transmitting it to other horses.

Indirect transmission is also possible if equipment or objects—including water troughs, hoses, stalls, tack, feed bunks, pastures, trailers, etc.—become contaminated and are shared between horses. People can also transmit the disease between horses via contaminated hands or materials (e.g. clothing).

Clinical signs and symptoms of Strangles in horses

Clinical signs and symptoms of Strangles include:


Nasal discharge

Swollen lymph nodes

(typically submandibular and retropharyngeal) that can develop abscesses

Difficulty swallowing

Loss of appetite

Occasionally the infection spreads to lymph nodes in the thorax or abdomen, resulting in a complication known as "bastard Strangles."

How is Strangles diagnosed?

If a horse is showing signs and symptoms, or has been exposed to Strangles, a PCR test (done by taking a sample from deep in the nostril or throat, using a swab or a rinse) and a lab “culture” (a lab test that helps to identify what might be causing an infection) are considered the best practice for a diagnosis. The combination helps to determine the actual status of a horse that:

  • has been exposed to Strangles,
  • is showing symptoms of Strangles, or
  • is in recovery.

Samples taken from the horse are sent to a lab for analysis.

Prevention and treatment of Strangles in horses

The traditional treatment for Strangles in horses is a course of antibiotics, such as penicillin, although the efficacy of this treatment remains controversial. Antibiotics are ineffective at eliminating the microbe completely and may result in a reduced immune response, potentially making horses treated with antibiotics more susceptible to relapse.

Vaccination helps to reduce the risk of Strangles. There are two kinds of Strangles vaccines available in Canada: a killed vaccine that is delivered intramuscularly (in the muscle) and a modified live vaccine that is delivered intranasally (up the nose).

Strangles is highly contagious and Streptococcus equi bacteria are able to survive in the envirornment, particularly in water sources or when protected from direct sunlight and disinfectants. This persistent bacteria can be a source of infection. In addition to vaccination, following a strict biosecurity protocol can help reduce the risk of a Strangles outbreak or minimize the impact of an emerging outbreak.

A Strangles control protocol may include:

Daily monitoring of the temperature of horses that may have come in contact with Strangles.
Immediately isolating
any horse showing signs of infection. Horses may begin to shed bacteria within 48 hours of developing a fever.
Isolating new horses on a property for two weeks following their arrival.
Regular monitoring, cleaning, and disinfecting of equipment and facilities, especially sources of water.

Strepvax II can help
protect your horse from Strangles.

Learn more about Strepvax II
Talk to your veterinarian

about whether a vaccination plan to help protect your horse against Strangles is needed.