An introduction to strangles
Strangles is a very common but unpleasant bacterial disease that can affect horses and ponies of all types. The best way to minimise its spread is through early detection and implementation of appropriate bio-security. Signs differ between individuals and can range from very mild (e.g. a transient fever) to dramatic (severe throat swelling causing asphyxia) in appearance.
Strangles can cause great distress to both the horse and its owner. It can be difficult for the vet to treat and can become a management nightmare for yard owners.
Signs to look out for:
- A high temperature, usually at least 102.5 -104°F or 39-40°C (this is usually the first clinical sign to occur)
- Depression and loss of appetite
- A runny nose (usually watery to begin with but becoming thick pus within a few days)
- A cough
- Swollen and painful glands under the jaw
- Difficulty in swallowing
- Abscesses in the throat area
- Difficulty in breathing and abnormal respiratory noises
NB: It is important to recognise that not all horses show all of these signs. Some may simply have a high temperature and seem off colour, so the disease can remain unrecognised until another horse is infected and shows more typical signs.
- Bacterial disease caused by Strep equi (Streptococcus equi subspecies equi)
- Close contact between horses or direct contamination of environment is required for spread
- Many horses on a yard may succumb (30-100%) as it is highly contagious
- Young (less than 5 years old) and elderly horses may be the first to be affected and may show more severe signs, although any horse may catch strangles
- Complications may occur in up to 20% horses
- May be fatal in a small number of cases
- 10% horses may become ‘carriers’, a source of future infection
- The incubation period is 3 – 10 days and clinical course about 3 weeks if untreated
Spread and containment in the enviroment
Strangles spreads principally by direct contact from horse to horse or horse to object to horse i.e. rubbing noses and sharing drinking troughs etc. Even horses kept together do not always all contract the disease, in the same way that not all members of a family all catch the same cold.
Just as important as horse-to-horse contact is spread of the infection by poor hygiene amongst handlers i.e. spread on clothes, buckets, tack and other contaminated kit. The bacteria that cause strangles can linger for several weeks in the environment so may persist in dirty stables.
Fortunately this infection is not airborne so, unlike influenza, it will not spread long distances without some kind of direct contact. Horses may shed bacteria while they are ‘incubating’ the disease a few days before they show any signs or for a few weeks after all their symptoms have resolved. Some horses become ‘carriers’ and harbour the infection in their respiratory tract. These carriers may shed bacteria for years without showing any overt signs.
Diagnosis is not easy to confirm. Presumptive diagnosis may be made if horses have a contagious respiratory disease with very high fevers and abscess formation in the throat area, and rapid spread between different in-contact animals. However, NOT ALL cases can be PROVEN to be caused by strangles, even when all clinical signs are highly suspicious; strangles may be confused with viral respiratory diseases.
Confirmation of the disease can only be made from laboratory tests on swabs of the nose or draining abscesses. Endoscopy is sometimes used to check inside the throat where the guttural pouches may be lavaged. This is especially useful to check for carriers.
Management of an individual case
- Isolate individual affected horses
- Keep the horse as comfortable as possible ~ good nursing care will help encourage them to eat and drink
- Put the hay and feed on the ground to aid drainage of discharges
- Give soft, wet, palatable feed that is easier to swallow with a sore throat and a little salt to encourage drinking
- Give Phenylbutazone (“bute) as directed by your vet to lower fever and reduce throat soreness and swelling that is causing discomfort swallowing
- ‘Hot-pack’ firm abscesses to encourage them to soften and burst. This may provide relief to the horse when the pressure building up is released and will speed up healing
- A vet is only really able to lance an abscess that is almost ready to burst and has softened and feels ‘fluidy’
- Clip / trim hair overlying an abscess so it is easier to keep clean when it does burst
- Flush draining abscesses daily with very dilute antiseptic solution (Hibiscrub at a dilution of 1 part Hibiscrub to 10 parts water) or salt water
- Protect the healthy skin around a draining abscess with regular cleaning and apply Vaseline around (not in) the wound
- Turn out is fine so long as pasture contamination or horses in neighbouring fields are not a concern: fresh air can help the affected horse, but can contaminate the grazing
What to do if there is an outbreak on your yard
Isolation is important, but often difficult to maintain, for up to a month after the last case occurs; other precautions include:
- Disinfectant foot bath outside isolation stables and yard entrance
- People looking after affected / isolated horses should ideally not handle other horses or at least change all outer clothing and wash hands before doing so
- The strangles bacteria will be destroyed by a hot wash so changing clothes will reduce risks of spread
- Cases of suspected strangles should be taken seriously and precautions regarding isolation should be observed until proven otherwise
- Monitor rectal temperature twice daily in all horses that you are concerned about and can easily check. A raised temperature may be the first clue that they may be about to develop signs
- Let people such as the vet, farrier, dentist, saddler, feed delivery etc. know before they come to the yard. They may prefer to make it the last visit of the day to avoid the risk of contamination to other yards
- Warn horse owners using adjoining fields or who ride close to the yard to keep their distance
- Avoid taking in-contact horses to shows where they may spread the disease to other horses and yards.
Actual veterinary treatment of strangles is limited. Anti-inflammatory medication such as phenylbutazone (“bute”) or Danilon (which is more palatable) as directed by your vet may be used. Sometimes other injections may be given intravenously by the vet when affected strangles case will not eat.
Use of antibiotics in cases of strangles is contraversial:
- Occasionally used in very early cases
- Clinical signs often recur when antibiotics are finished
- Disease may be prolonged if abscesses are already present (these may be internal and not known to be present)
- Horses trated with antibiotics will not develop any immunity and may therefore develop the disease later
- Occasionally antibiotics must be used despite the risks because of life threatening complications or in a persistent case which shows no signs of resolving.
Complications are unusual but can be very serious:
Respiratory distress: Swelling at the back of the throat may cause difficulty swallowing and, in more severe cases, difficulty breathing
Bastard strangles: Severe illness with spread of abscesses to other areas of the body
Purpura Haemorrhagica: Serious illness of the immune system that can follow on about a month after – 1-2% of strangles cases can be affected. The clinical signs of purpura haemorrhagica vary, but can include:
- oedema (soft swelling) of the head, limbs and other parts of the body
- tiny haemorrhages on the lips, gums and other mucous membranes e.g. around the eye
- stiffness and reluctance to move
blood and serum may ooze through the skin and areas of skin may die leaving ugly raw areas.
It is not a disease that will sneak up on you without you being aware something is wrong with your horse. It is unpleasantly obvious that something serious is wrong.
The most obvious sign is the oedema; even spindly thoroughbred legs will appear as thick as tree trunks. This oedema is caused by fluid leakage within the body and can have other serious effects; eating and breathing can be impaired. Severe cases can show signs of colic or kidney disease. In the early stages or milder cases, the muscle stiffness and reluctance to move may be confused with laminitis.
Overall there are limitations to the current control measures available to prevent the disease. As well as watching for signs of sickness and testing horses these include:
- Avoiding contact with horses of unknown origin
- Ensuring a yard does not become overcrowded. Close contact between horses is an effective method of spreading strangles (and other infections) so should be minimised
- If new horses are introduced, keeping them in isolation initially.
In the real world many anti-strangles precautions may seem impractical, but they should still be followed as far as possible. There is a vaccine against strangles and is available for use where necessary. If the vaccine is given it is best given to all the horses on a yard and requires regular boosters. If you are considering this option call, Bell Equine on 01622 813700 to talk to one of our vets who can advise you on what is the best course of action for your particular situation. The best advice has to be to talk to Bell Equine for guidance relating to your individual situation.
- How long should a new horse be separated from the others to know that it is not ‘brewing’ strangles?
Incubation period is 3-10days from exposure. If a horse has not spiked a fever or shown any signs of ill health in 2 weeks it should be safe to introduce to the herd. A horse may, however, be a silent ‘carrier’ and bring strangles into a yard without showing signs.
- How do I know if a horse is a ‘carrier’ that is new to the yard or after an outbreak?
In theory vets can test if a horse is a carrier by taking swabs from the back of the airway or by collecting samples via an endoscope. In most (but not all) cases if three swabs (usually taken at 5-7 day intervals over a two week period) are negative, the horse is clear. This involves effort, expense and cannot guarantee a horse is free from infection so vigilance is still required.
- There’s a horse on the yard that is showing signs that might be strangles but it has not been proven by the vet. Do we have to shut down the yard?
The mere mention of the word ‘strangles’ can cause a lot of bad feeling and worry on a yard. Strangles can be unpleasant and painful for the horse, difficult for the vet to treat and a management nightmare for yard owners.
Once one horse has been diagnosed with this infectious disease, all other horses in contact are at risk. Ideally the affected horse should be isolated and the stable yard should be closed to prevent spread. Within reason, until you are given the all clear, it is best to start taking precautions. Delay in preventing further spread of the disease results in more horses being exposed and a more serious and longer lasting problem. Isolate horses that are showing signs and those that have been in direct contact. If it turns out to be strangles this will significantly reduce spread through the yard.
It is also worth considering cancelling excursions from the yard to avoid spreading the disease to other horses that may take it back to their yards, just as you would appreciate others showing the same consideration, so that your horse does not ‘catch something’ at a show.
One difficulty is that there is no legal notification requirement for strangles. If individuals elect to carry on regardless despite persisting infection they cannot be prevented from so doing! All this does is increase the potential for further spread.
- How do I know which of the healthy horses to isolate?
Horses that have been in direct contact with a horse that has developed strangles may be ‘incubating’ strangles and may be infectious to others. This includes contact in the few days before the horse may have started showing signs. Taking rectal temperatures twice daily of all horses (if it is safe to do so) may allow earliest detection of a horse not yet showing other symptoms. This allows early isolation and reduces spread.
- Does the vet have to examine my horse if I think he has strangles?
It is advisable to speak to a vet and describe your horse’s symptoms and yard situation to decide whether you need a visit. If you are not sure whether it is strangles, it is a good idea for a vet to come and examine the horse in case there is another disease involved.
If the vet thinks that it is suspicious of strangles they can take swabs from some affected horses. It is a good idea to try to confirm or disprove the diagnosis so that a yard is not ‘shut down’ unnecessarily.
If your horse develops difficulty breathing or very noisy breathing, a vet needs to examine your horse to make sure that there is not a risk that the airway will become blocked requiring emergency treatment. If your horse refuses to eat or swallow, the vet may need to inject “bute” to start to reduce the swelling in the throat and make your horse more comfortable so that you can then administer “bute” in the feed.
If you already know that your horse has been exposed to strangles and the situation is under control, telephone advice may be sufficient.
- My horse has had strangles before, can he get it again?
Most horses will be fully protected from catching strangles again for up to 5years. It is unusual for horses to catch strangles more than once.
- How should I clean abscess discharges?
Wipe and flush daily with very dilute iodine or Hibiscrub or salt water. The horse may resent this and warm water may help. It is not worth a battle if the horse will not allow it.
- There is a massive hole where the abscess burst, is that ok?
The wound may appear distressingly large but this is very common and will fill in and heal remarkably quickly.
- What disinfectant should I use in footbaths or to clean stable, headcollars etc?
Virkon or Trigene are effective.
- How long until the paddock is safe for other horses?
A paddock (especially fences, gates, water troughs, etc) can remain contaminated for up to two months (less in hot weather).
Strangles in summary
I think my horse has strangles
- No horses should come onto or leave the yard
- Staff and owners should not come into contact with horses from other yards
- Owners of ALL horses should be notified as soon as possible
Sort horses and equipment into three groups:
- Presumed infected horses that have shown clinical signs consistent with strangles
- Horses that have had direct or indirect contact with the infected horses in the red group, but are not showing clinical signs
- Horses that remained detached from those in RED and AMBER groups, without any known direct or indirect contact and which are not demponstrating clinical signs
- SWABS: A nasopharyngeal swab is passed up the horses nose to the pharynx to see if the bacteria S.equi (strangles) is present. This is good at detecting infectious horses but DOES NOT always identify carriers
- BLOOD SAMPLE: A blood test is a good way to see if a horse has been recently infected with strangles. Howver, horses that have been infected within the last 14 days may give a false negative result. It is therefore good for screening horses coming on to a new yard, but not always useful in an outbreak.
When is my yard considered ‘free’ from strangles?
It is recommended that all horses are tested 28 days after the last horse has shown clinical signs of strangles. To be considered free from strangles a horse must EITHER have three negative nasopharyngeal swabs one week apart OR one negative guttural pouch wash.
Guttural pouch washes are very useful in finding carriers of strangles.