Strangles in Horses

Strangles is a contagious bacterial disease affecting horses.  It is caused by the bacteria Streptococcus equi subspecies equi. Strangles is spread by direct contact with infected horses, or by contact with infected objects (eg buckets, water points, hands).  Younger horses and horses with a compromised immune system are more likely to be affected.  Whilst the morbidity (how sick the horse gets) is high, the mortality rates of outbreaks are generally low. Following illness with Strangles a long lasting immunity (up to 5 years) can develop and future infections aren’t as severe.    Vaccination against strangles is possible to reduce the severity of the disease, however vaccination needs to be continued annually.

Horses with Strangles develop a fever, and can go off their food.  A mucoid, snotty discharge can develop from one or both nostrils and the glands under their neck (the lymph nodes) swell up.  Abscesses go on to form in the lymph nodes.  It can take 1-2 weeks for the abscesses to develop and rupture, and in this time the horse can develop a cough, have trouble eating and even trouble breathing.

Strangles can be treated with anti-inflammatories in the early stages of the disease, to reduce the fever and make the horse feel better.  Antibiotics can be prescribed later in the course of the disease if there are complications, however generally the disease can be allowed to run its course and allow a good immunity to develop. Once the abscesses burst or are surgically opened to drain, flushing them with iodine helps.

Complications from Strangles can include the requirement for a tracheostomy to assist with breathing difficulties, trouble eating requiring an adjusted diet, formation of chondroids in the guttural pouches (hardened pus), purpura haemorrhagica (a reaction to infection which can be fatal), and spread of the infection causing other abscesses throughout the body (bastard Strangles).

Strangles is easily transmitted through contaminated equipment and nose to nose contact with infected horses.  The incubation period after picking up the bacteria is 3-21 days, and horses can shed for 4-6 weeks following infection.  Fortunately the bacteria don’t survive long in the environment, so resting paddocks for 4-6 weeks can help reduce spread.  However some horses can develop a persistent carrier state which can lead to intermittent shedding  and be a source of infection.  These horses may not show any signs of infection.

When dealing with an outbreak it is important to test the infected horse and all horses that have been in contact with that horse.  This allows the extent of the outbreak to be determined and to allow control measures to be taken.  Blood tests can be used to determine if a horse has been exposed (or vaccinated) however a sample taken from the back of the horse’s throat or of its nasal discharge that grows the bacteria is the most accurate way of determining if the horse is carrying and shedding the bacteria.

Steps to help control an outbreak include:

Separate all horses that have been in contact with the infected horse and stop further contact.

  • Divide horses into 3 separate groups:
    • Monitor temperatures twice daily, as the fever will peak 2-3 days prior to shedding of the bacteria.
    • These horses should be separated by at least 10m from potentially infected horses, and strict hygiene followed.
    • Red Zone:-Sick horses.
    • Orange Zone:- In contact but not showing signs.
    • Green Zone:- Horses that haven’t had contact.
  • Treat the healthy horses first, and the sick horses last.  Only use certain equipment for infected horses.

Disinfect all equipment, water troughs, feeders, gates and fencing using bleach or other antiseptic product (eg. Virkon, Trigene, Chlorhexidine).

Rest paddocks 4-6 weeks prior to introducing new horses.

Perform repeat tests of affected horses to make certain they are no longer shedding.

Isolation should continue for 1 month after no more new cases occur.

Strangles can be prevented by following good hygiene practices and by vaccinating your horses.

Have a quarantine period for new horses coming onto the property of 3-4 weeks.

Testing of new horses can also help pick up carriers not showing signs.

When travelling to horse events be aware of good hygiene practices:

  • Provide your own equipment and buckets.
  • Avoid tying or yarding within contact distance of other horses if available.
  • Monitor your horse’s temperature and health whilst you are away.
  • When returning home, shower and change your clothes, as well as clean your shoes, prior to visiting your other horses.  A 2 week isolation period would also be ideal to prevent spread of Strangles at home.

Vaccinate your horses with the intra-muscular Strangles vaccination, 3 doses fortnightly for the initial course. In the case of an outbreak on the property, consult with your vet to determine if vaccination should be used at this time, to reduce the risks of purpura haemorhaggica.

Strangles is a Notifiable Disease, meaning that if you have a reasonable suspicion of the disease you should confidentially report it to your District Veterinary Officer and contact your vet.

References & Further Reading:

Equine Biosecurity and Best health Practice – For Equine Owners- Agriculture Victoria Website.

Michael Hewetson BSC, BVSC, DIPL.ECEIM University of Helsinki.  NEW INSIGHTS INTO AN OLD DISEASE – STRANGLES. Proceedings of the Belgian Equine Practitioners Society (BEPS) – 2014.