What is Strangles?
This is a highly contagious disease of the upper respiratory tract, unique to the horse family, caused by the bacterium Streptococcus equi equi. The infection can be spread by horse-to-horse contact or via humans, tack, feed utensils and other items which may contact infected horses. It is the most commonly diagnosed bacterial disease in horses with a worldwide distribution. In the United Kingdom there are an estimated 200 to 400 outbreaks each year.
Which horses are most often affected?
The disease can occur in horses of any age, however it is most commonly seen in young horses. Most horses develop a varying a degree of immunity following infection, and this may last several years. Older or debilitated horses are at an increased risk of infection or re-infection. This variation in immunity explains why some horses on an infected yard look very ill and others appear completely unaffected.
What signs may suggest Strangles?
- Fever (>38.3oC).
- Nasal discharge (serous to purulent) with or without an ocular discharge.
- Lack of appetite.
- Enlarged lymph glands.
What do I do if I think my horse has Strangles?
Isolate your horse from other horses in close contact and notify us immediately. Aggressive early treatment may sometimes prevent full development of the disease. We can also help develop a quarantine and detection system for your stables and so minimise the risk of the disease spreading further.
How does the disease progress?
The lymph glands become firm, swollen and painful. This may result in the horse keeping its head low with neck extended to relieve the pressure put on the windpipe by the swollen glands. Difficulty in swallowing may also be apparent. In most cases the glands will then burst accompanied by a marked improvement in demeanour, and subsequent return to good health. 95% of horses will clear themselves completely of infection within a month. However the remaining 5% may remain carriers for months or even years, and these carriers are often the source of new outbreaks. For this reason we strongly recommend that every recovered case is swabbed to ensure freedom from infection before it is released from isolation.
How is the diagnosis confirmed?
In many situations a preliminary diagnosis can be made based of classical signs, however abscessation may occur later in the course of the disease or may be clinically in apparent. In order to confirm the presence of the Strangles bacterium sequential swabs may be taken from the back of the horses throat (via the nose) or samples taken from the Guttural Pouches using an endoscope. These samples will then be sent to a laboratory to be cultured and screened for the DNA specific to the Strangles bacterium. One sample is not always enough to confirm the presence of this disease and for this reason The Horserace Betting Levy Board has issued “Strangles Guidelines”.
What are the Guttural Pouches?
- Cavities which are extensions of the auditory/Eustacian tube (one on each side of the head), have a capacity between 300 and 500 ml and lie at the base of the skull.
- They connect with the horse’s throat via a valve that opens when the horse swallows and so promotes drainage during grazing.
- Their exact function is not fully understood however it is believed to be involved with controlling blood pressure and temperature within the head.
How is Strangles treated?
Although caused by a bacterium, use of antibiotics is not always beneficial. The vet will decide on their use depending on the stage and severity of the disease. Placing hot compresses over the lymph glands will hasten development of the abscess, and encourage them to burst or allow them to be lanced. The opened cavity can then be flushed and allowed to heal naturally. Anti inflammatories will often be used to bring the temperature down and relieve the pain associated with these abscesses.
Are there any possible complications?
Following infection most horses will return to normal health relatively quickly, however in as many as 20% complications may occur. Some of these may be fatal. Empyema occurs when a lymph gland ruptures through the floor of the guttural pouch releasing pus and bacteria into the cavity. The consistency of this material will often prevent it from draining easily through the valve into the throat (the slit in the middle of the picture on the left is the opening to the right guttural pouch). The infectious material dries out resulting in hard nuggets of pus containing bacteria known as chondroids. Removal of chondroids can be a difficult and expensive job. The organism can continue living within the pouch. Effected horses (silent carriers) carry the infection undetected and can be responsible for maintaining a Strangles outbreak within a yard for many months. The only way of identifying such a persistent infection involves examining the inside of the guttural pouch with an endoscope as seen in this picture on the right.
Bastard strangles occurs when the Strangles bacterium travels to another part of the horse’s body via the blood stream and develops a separate site of infection. This may occur in any part of the body but is most commonly recognised in the heart muscle, the liver, the lymph nodes within the abdomen, and the lungs. Aggressive veterinary treatment is required to treat these animals successfully.
Purpura haemorrhagica is an unusual immune reaction to the Strangles bacterium and causes extensive damage to blood vessels. This results in painful swelling of the head and limbs, and variable areas of apparently spontaneous bruising. Severe circulatory problems may subsequently develop.
How do I prevent the disease occurring on my yard?
Prevention of the disease or its spread primarily depends upon good management. New horses should be isolated for 2-3 weeks and their temperatures checked regularly. Any horse which shows suspicious signs of illness (high temperature, nasal discharge, difficulty in swallowing, swollen throat or glands) should be isolated until strangles is confirmed or ruled out by veterinary examinations and laboratory investigations. Any horse which has strangles should be immediately isolated from all other horses. It should have its own water and feed mangers, grooming kit and tack and no equipment used for the affected horse should be allowed near other horses. One person should look after the affected horse(s) and avoid contact with all other horses. All equipment, stables, fences, trailers, etc. should be thoroughly disinfected using an approved disinfectant (eg. Virkon).
Unfortunately, some horses become symptom-less persistent carriers of Streptococcus equi, most commonly in their guttural pouches (see above), and can infect horses intermittently although showing no signs of infection themselves. This is probably the most important cause of infection recurring at intervals of several months, after apparent clearance. Part of the clearance process for recovered cases should therefore be the collection of deep nasopharyngeal swab and guttural pouch wash samples for laboratory investigations.
Can I vaccinate against Strangles?
A new vaccine has now become licensed for use in UK and, although not 100% protective, does offer significant defence against strangles infection.
Do please phone the practice to discuss your particular situation.
Code of Practice – Control of Strangles Infections
Since 1978, the Horserace Betting Levy Board (HBLB) has annually updated and produced its highly successful Code of Practice for the control of equine venereal diseases and now includes guidelines on strangles. This contains detailed advice and recommendations on the disease and its effects, diagnosis, control and prevention. Your veterinary surgeon will have a copy of the Code and copies may be obtained via the Thoroughbred Breeders Association or the British Horse Society. Although a voluntary Code it has become the industry standard for the benefit of all and all horse breeders should read it and follow its advice.
DISCLAIMER: This advice is intended for use by registered clients of Priors Farm only. The advice offered is general advice only. Priors Farm clients who wish to discuss the individual circumstances of their horse should contact the office. To speak to a vet please phone between 8.30 – 10.00 am on weekday mornings.