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Streptococcus Equi Infection Strangles

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Streptococcus equi cultureOverview:

Strangles is a highly contagious disease of the respiratory tract and the lymph nodes primarily surrounding the throat. The disease is found worldwide in horses of all ages, although younger horses are most susceptible.

Strangles is caused by the bacteria Streptococcus equi, which may be transmitted during a horse’s contact with discharges from the lymph nodes or nostrils of infected horses or by contact with equipment used on infected horses. Infection typically causes very high fever, loss of appetite, thick mucus and pus-like nasal discharge, and swollen or abscessed lymph nodes surrounding the throat.

Strangles usually responds to attentive nursing and — in some cases — antibiotics. Barring complications such as “bastard strangles,” horses usually survive this infection.

Horses with bastard strangles get abscesses in such places as the brain, abdominal cavity, and chest. With such complications, a horse may die from infection of the central nervous system, infection of the abdominal cavity, pneumonia, heart disease, sepsis, or overwhelming infection of the blood stream, and asphyxiation caused by the compression of the pharynx or larynx by swollen lymph nodes.

Strangles is best prevented by the strict isolation of horses thought to have the disease, and is prevented or ameliorated by vaccination. Vaccination is recommended especially for horses living in or traveling to areas in which the disease is endemic.

Clinical Signs:

Common clinical signs of strangles include pyrexia, thick mucus and purulent nasal discharge, depression, anorexia, and swelling and abscess formation in the retropharyngeal, submandibular, and submaxillary lymph nodes.

Horses with strangles will often stand with necks stretched out to cope with pain, difficulty breathing, and difficulty swallowing caused by the pressure of enlarged lymph nodes on the pharynx.


Horses with strangles develop a fever that can be as high as 106¦ F, or 41¦ C, thick mucus and puss-like nasal discharge, depression, decreased appetite, and swelling and abscess formation in the lymph nodes surrounding the throat.

Horses with strangles will often stand with necks stretched out to cope with pain, difficulty breathing, and difficulty swallowing caused by the pressure of enlarged lymph nodes on the throat.


Strangles is highly contagious and found worldwide in horses of all ages. Younger horses between one to five years of age are most susceptible to infection.

Horses contract strangles by inhaling or ingesting the gram-positive bacteria Streptococcus equi. This is spread through contact with other horses, infected horse tack and used Western saddles for sale that haven’t been disinfected properly.  After the bacteria incubate for a week or less, they often cause symptoms such as fever and decreased appetite.

Once infected, the bacteria travel to the respiratory tract and pharynx, causing significant inflammation and pain. Subsequently, the bacteria infect the lymph nodes surrounding the throat, or the submandibular, submaxillary, and retropharyngeal lymph nodes, causing them to swell and become abscessed.

The disease generally lasts two weeks from the time that abscesses form and begin to drain.

In cases of “bastard strangles,” abscesses form in other parts of the body, including the chest and abdomen. These abscesses may open up and drain, causing severe, life-threatening infection and inflammation.

Such cases are very difficult to treat, and may lead to death. Other causes of death include central nervous system infections, heart disease, pneumonia, asphyxiation, and sepsis, which is an overwhelming infection of the blood stream.


Strangles is usually diagnosed by means of its clinical signs, which include a fever of 106¦ F, or 41¦ C, and lymph nodes that are swollen or abscessed, and oozing serum, pus, and fluid.

Identifying Streptococcus equi bacteria in the discharge or pus coming from ruptured or surgically lanced lymph nodes, or in discharge from the nostrils, provides a definitive diagnosis of strangles.


For horses that develop strangles without complications, the disease usually runs its course to a full recovery. Horses that develop complications or “bastard strangles” become abscessed and infected throughout the body and in vital organs that include the lungs, kidneys, and brain.

In these cases, horses may die from central nervous system infection, organ failure, sepsis, or an overwhelming infection of the blood stream, heart disease, and pneumonia.

Transmission or Cause:

Streptococcus equi is transmitted by means of direct contact of horses with the nostril and lymph node discharge of other infected horses. Horses may also become infected by buckets, halters, and feeding and other equipment that has come into direct contact with an infected horse.

Streptococcus equi bacteria are very contagious, and any horse suspected of having strangles should be placed in strict isolation from all other horses.


Treatment of Streptococcus equi varies depending on the case. Antibiotic therapy may be used in cases in which the lymph nodes have not yet abscessed and the horse is in the early stage of disease.

Early treatment with antibiotics may actually stop the formation of abscesses and prevent infection of the lymph nodes in horses only recently exposed to the bacteria.

If the lymph nodes have already abscessed, then the use of antibiotics may only prolong the course of the disease. Frequently, veterinarians will not administer antibiotics in these cases, unless they involve chronic illness or threaten to cause secondary bacterial infections.

Since the use of antibiotics is controversial in many cases, the examining veterinarian will determine if antibiotics are required, as well as which antibiotic is best for a particular case.

Horses with strangles should be rested in their stalls and nursed throughout the course of the disease. A veterinarian will often lance abscesses that are fully developed but not yet ruptured.

Applying hot compresses to swollen lymph nodes will help quicken the course of abscess formation, allowing a veterinarian to lance abscesses earlier. Horses unable to breath properly may require a tracheostomy tube, which is inserted below swollen lymph nodes directly into the trachea.

A horse may breath easily through the tube. Tracheostomy tubes require a great deal or management and they must be carefully and frequently monitored and changed.


Various vaccines have been developed for strangles. These vaccines may help reduce the severity of symptoms, shorten the duration of the disease, and reduce by 50 percent the chances of infection during an outbreak.

However, vaccination often causes a reaction at the site of injection and is recommended only for horses on farms, for horses in areas that have experienced outbreaks, or for horses being transported to areas considered to be at high risk.

Streptococcus equi is killed by sunlight, disinfectant, or desiccation. Surfaces and equipment that have come into contact with infected horses should be thoroughly cleaned. Horses with strangles should be strictly isolated.

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