Strangles

 This article provides the following information on the horse disease strangles (also known as equine strangles):

  • 1.0 What is Strangles?
  • 2.0 Symptoms
  • 3.0 Diagnosis and Treatment
  • 4.0 Prevention
  • 5.0 Complications

For information on other equine illnesses, click on horse disease.

1.0 What is Strangles?

Strangles is a highly contagious disease which is caused by a bacterial infection (the bacterium is known as 'streptococcus equi'). The bacteria  infects the lymph nodes in the upper respiratory tract, which become swollen and may become abscessed. It is the most common infectious equine disease in the world (source: Strangles Org).

Young horses ( between 1 and 5 years of age) and very old horses are most easily infected and tend to have more severe cases of the disease due to their immune systems being less resistant, but horses of any age can become ill with the disease. Approximately 75% of horses which have been infected by strangles are resistant to future infections.

2.0 Symptoms

The first symptoms of stranges normally become evident 2-6 days after the horse is infected, but in some cases can take up to 14 days. The symptoms are as follows:

  • Nasal discharge. In the early stages of the disease, there is a thin, watery discharge from the horse's nostrils. This soon changes to a thick, yellow discharge.
  • Swelling under the jaws. The upper respiratory lymph nodes become enlarged. This is often most noticeable between the jawbones.
  • Strangling sounds. The swollen lymph nodes restricts the airway, resulting in the horse making 'strangling sounds' as it breaths. The name 'strangles' comes from this sound. In more severe cases, obstruction occurs not only from swollen lymph nodes, but can also be caused by damage to throat muscles by the abscesses or by drainage of pus into the airways when internal abscesses burst.
  • Cough. In same cases, the horse may develop a cough.
  • High fever. This is one of the earliest signs of strangles, with temperatures up to 41°C. However, as high temperatures are associated with many other types of infection, this is not a strong indication of infection with strangles unless you have reason to believe that the horse has been exposed to the illness (e.g. been in contact with an infected horse).
  • Poor appetite or Difficulty in swallowing. Appetite is depressed not only by the illness, but also by the infection making swallowing painfull in the later stages of the disease.
  • General depression.

The first three of these symptoms are an indication of strangles. The last four can be caused by many other illnesses as well, so are not in themselves a strong indication of the strangles disease, although they are an indication that medical attention is required.

Some infected horses have only mild versions of the disease and may only show a nasal discharge without swelling of the lymph nodes. Mild cases of strangles can be difficult to detect, as they may not display the classic symptoms and can be incorrectly attributed to other diseases (e.g. flu). This can result in the infection spreading throughout the stables and outside before it is correctly diagnosed.

If treated promptly, the horse should recover well. If the disease is left untreated:

  • The lymph nodes will become abscessed one to two weeks after the onset of the illness.
  • Abscessed lymph nodes will then rupture and drain, releasing a fluid which contains the infectious bacteria and is highly contagious.
  • In rare cases, other parts of the horse (e.g. lungs, internal organs, even the brain) will becomed abscessed as well. This is known as 'bastard strangles'; it is usually fatal but fortunately it is uncommon.

3.0 Diagnosis and Treatment

A veterinarian can make a preliminary diagnosis based on the symptoms (see above). The initial diagnosis can be confirmed by taking a sample of the nasal fluids (from the back of the horse's naval cavity - nasopharynx) or abscess fluid (if the disease has progressed to that stage) and sending it into a laboratory which can examine the fluid for presence of the strangles bacteria. In 2008, a blood test for strangles was developed in the UK to allow quick and early testing.

If you suspect a horse has strangles, it should be immediately isolated from other horses (to prevent the spread of the disease). The disease is highly contagious, so a responsible horse owner will take immediate action to prevent other horses from being affected, including both his/her own horses and horses with other owners..

You should have a veterinarian examine the horse as soon as possible:

  • Diagnosis and Treatment. This should be done as soon as possible, since treatment in the early stages will greatly reduce the severity and duration of the illness.
  • Quarantine. A confirmed diagnosis will indicate that the affected horse should be isolated, along with any other horses that it may have infected in turn. In many countries, the veterinarian is required to notify the authorities, so that additional steps can be taken to identify the origin of the infection and prevent further spread.
  • Inform other Horse Owners. Although one does not want to alarm people unneccessarily, as a matter of courtesy and responsibility one should contact the owners of other horses who may have been in contact with your horse to advise them that they should watch out for any symptoms. Likewise, if your horse has been at a show or other event, one should contact the show organisers and inform them of the facts. Even if your horse has not infected other horses, it is still likely that whichever horse infected your horse may have infected other horses at the same time. Likewise, if you have immediate neighbors with horses, one should let them know as well.

The nature of the treatment will depend on how far the illness has progressed (what stage it is in).

  • Early Stages. In the early stages, the standard treatment is antibiotics. If administered at this point, lymph node abscesses can be prevented. if the vet has provided the antibiotics to yourself to administer, ensure that you give them in the correct quantity and do not stop antibiotic treatment too soon.
  • Late Diagnosis. If the disease is not treated prior to the point where the lymph nodes are enlarged and abscessed, antibiotic treatment may no longer be effective and may in fact simply prolong the duration of the illness (by preventing or slowing abscesses from reaching the drainage stage). In this case, treatment will consist of opening, drainage and cleaning of abscesses and surrounding area, including flushing open abscesses with an antiseptic solution. Abscesses can often be opened using warm packs but in some cases the veterinarian will decide that surgical opening is required.
  • Symptomatic Treatment. In both cases, treatment is likely to include medication to relieve the symptoms. For example, non-steroidal anti-inflammatory medication to control their increased body temperature.
  • Comfort. The horse should be kept in a warm and dry environment, as physical stress will reduce the ability of the immune system to resist and recover from the illness. The use of soft, palatable foods will help the horse to eat. If you use feed, especially peleted feed, it may be adviseable to soak it so that it becomes softer, and so that the risk of dehydration is reduced. However, first discuss with your vet any changes to the feeding regime.

4.0 Prevention

Strangles is a contagious disease, which is caught from other horses (direct contact) or from items they have been in contact with (indirect contact). Consequently, the best prevention is to:

  • Avoid infected horses. Avoid contact with infected horses or horses which may be infected. If you see a horse showing the symptoms of strangles nearby, immediately move your horse away and confirm with the owner of the other horse if it is potentially infected.
  • Avoid previously infected horses. A horse which has recovered from the disease will still have the bacteria and remain contagious for up to a month after it is no longer showing any symptoms. Consequently, infected horses should continue to be isolated from other horses for a period of time even after they appear to have fully recovered. In case of chronic infections (see section 5 below), previously infected horses may be contagious for years.
  • Avoid areas and equipment used by infected horses. The nasal discharge and material from abscesses contain the bacteria and consequently can infect your horse. Any pastures, stalls, feed troughs, water buckets, tack, mucking out forks and wheelbarrows, and so on which have been in contact with an infected horse can pass on the disease. Consequently, all such areas and items should be avoided. Note that the bacteria can survive up to 8 weeks (source: Strangles Factsheet ), so any contaminated items need to be isolated for at least this long after the time of contamination.
  • Isolate questionable horses. If horses have a vague or unknown health history, the safest option is to isolate them (and any equipment or other items they come in contact with) for up to 6 weeks. Although there are tests to determine if a horse is infected (using nasal swabs), such tests are not 100% reliable (as infected horses do not always shed the bacteria continuously) so it is recommended that a negative result on at least three swabs over a 14-day period is required before a negative sway result is accepted.
  • Isolate premises. To prevent the spread of the disease to other areas, no horses should enter or leave the premises until all horses have recovered and are no longer contagious (see above point for details).
  • Hygine. If one has an infected horse, use of gloves and foot dips to avoid spreading infectious fluids is adviseable. One should also obtain and use a disinfectant effective against the strangles bacteria (consult your veterinarian to identify and obtain an appropriate disinfectant).
  • Vaccinations. Strangels vaccines are available but are not 100% effective. However, they do offer some protection from contacting the disease. Furthermore, if a vaccinated horse does contact the disease, the illness tends to be less severe.
  • Preventive antibiotics. If you believe that your horse has been in contact with an infected horse (e.g. at a show or competition), contact your veterinarian to start a preventive antibiotic treatment for a minimum of six days duration.
  • General health and conditions. Although the disease is highly contagious, infected horses do not always develop the disease. Horses which are strong, healthy and free of stress are more likely to have strong immune systems which can resist the illness and prevent its development. It is for this reason that outbreaks of strangles is more likely to occur with the onset of cold and damp weather, which can stress horses and reduce their immune system capacity.
     

5.0 Complications

Approximately 10% of untreated horses die, usually due to a secondary infection causing pneumonia. Even in horses which recover there are a number of complications which sometimes occur (see section 3 of Horse Strangles for discussion of various types).

In some cases, horses can become chronic carriers of the disease after infection. This can be tested for by sequential nasopharyngeal swabs, although a more reliable test is endoscopic examination of guttural pouches. Some veterinarians advise examination and flushing (of guttural pouches, sinus openings and trachea) to reduce the risk of the horse becoming a chronic carrier.
 

During the illness and for some time afterwards (until the horse's strength and immune systems have fully recovered), the horse is at greater risk of other illnesses. Therefore, additional care should be taken to protect the horse from illness or stress during this period.

Treatment of the abscesses (see section 3 above) is important not only for treatment of the disease itself, but also to prevent secondary infections.