Note for Pet Owners:

This information is provided by Provet for educational purposes only.

You should seek the advice of your veterinarian if your horse (or pony) is ill as only he or she can correctly advise on the diagnosis and recommend the treatment that is most appropriate for your horse..

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Strangles (also called equine distemper) is a highly infectious upper respiratory disease which affects horses and ponies. 

e cause of "strangles" is a bacterium : Streptococcus equi. The disease is transmitted from infected horses (following direct contact with pus, through aerosol spread due to coughing or the nasal discharge)  and through contamination of the environment. The bacteria can be shed from an infected horse for over 6 weeks even though the horse may not be showing signs. 

Breed Occurrence
The disease can affect any horse or pony that is exposed to an infected animal or an environment contaminated with the bacteria.


The signs associated with strangles include :

  • Soft tissue swellings in the neck - due to enlargement of the lymph nodes. These can burst forming discharging abscesses.
  • Fever
  • Nasal discharge - initially serous, but later mucopurulent
  • Cough
  • General depression
  • Anorexia; reluctant to swallow food due to pain
  • Increased respiratory noise during breathing

Some horses may not show signs and may be carriers of the disease.

Occasionally horses develop an allergic reaction to Streptolysin O , a toxin produced by the bacteria S.equi - a condition called purpura haemorrhagica. 1-2 months following strangles they develop :

  • Stiffness 
  • Muscle pain
  • Reluctance to walk or move head
  • Oedema (fluid-filling) of the dependent parts of the body (the legs , and the underside of the chest, abdomen and prepuce in males)
  • Weals (small lumps) over the body
  • Haemorrhages of the visible mucous membranes (eg eyes, gums, vulva, prepuce)

Most horses will recover fully from strangles, but death can occur - usually as a result of complications.

The bacteria can survive for long periods of time (months) in the environment, and on objects such as buckets, tack, drinking troughs, and so re-infection is likely in stables. Although the disease usually affects the upper respiratory system, it can progress locally to involve the lungs (pneumonia) or guttural pouch. Chronic recurrent cases and asymptomatic carriers often have infection localised in their guttural pouches.

In some cases the infection may spread via the lymphatic system  to other parts of the body resulting in infection of lymph nodes in the gastrointestinal tract, and even other organs, including the brain. 

When  strangles proves fatal. These complications are most likely to occur in young foals with immature immune-systems or old debilitated horses.

Diagnosis can be made from the clinical signs and also from identifying the organism by microbiological culture of pus, or swabs taken from the respiratory tract. The guttural pouch may need to be examined using an endoscope, to confirm localised infection

The treatment of choice is antibiotics - usually penicillin.  All infected horses and in-contact horses should be isolated from other stock because the disease is so contagious. In countries in which a vaccine is available this should be given to suspect in-contacts which doe not develop signs of infection.

Treatment of purpura haemorrhagica involves :

  • Long term antibiotics - penicillin - (weeks)
  • Long term corticosteroids (weeks)

A vaccine is available in some parts of the world (eg USA) but it only confers temporary immunity and can not be used for long term prevention of infection.

Most horses will recover provided treatment is given as soon as possible.

Long term problems

A chronic carrier state or recurrent, chronic disease may be long term problems if the guttural pouch becomes infected.


Updated October 2013