March 17, 2026, 10:47 am | Read time: 5 minutes
A horse appears calmer, eats poorly, and has a slight nasal discharge—seems harmless. But this is often how strangles, a highly contagious infection, begins. What follows quickly becomes serious: fever, painful swelling—and the risk of infection for the entire stable. PETBOOK explains what is important now.
What Happens in a Horse’s Body During a Strangles Infection?
Strangles is a bacterial infectious disease that primarily affects the horse’s upper respiratory tract, including areas such as the nose and throat. These organs typically have important functions, like filtering and warming inhaled air.
Strangles is caused by the bacterium Streptococcus equi equi. When this pathogen enters the body, it infects the mucous membranes of the respiratory tract and spreads to the surrounding lymph nodes. The tricky part is that strangles often leads to inflammation of these lymph nodes, causing them to fill with pus. This results in what are known as abscesses, or encapsulated pus collections.
In some cases, these abscesses can rupture—either externally or into internal areas like the guttural pouch. The guttural pouch is an air-filled extension of the eustachian tube in horses. If pus accumulates there, it can complicate the course of the disease.1
Why Do Horses Get Strangles?
The cause of strangles is clear: the bacterium Streptococcus equi equi. It is found worldwide and is highly contagious. Transmission can occur in various ways. It often happens through direct contact between horses, such as via nasal secretions or coughing. Indirect transmissions are also possible, for example, through shared items like water buckets in the paddock. Humans can also carry the bacterium on their hands or clothing without becoming ill themselves.
Additionally, so-called “silent carriers” can transmit the disease. These are horses that have been infected and recovered but remain infectious. Pus stones can remain in their guttural pouches. These are often unproblematic for the affected horse but can infect other horses.2
Young horses are particularly susceptible. In stables, outbreaks can quickly occur, affecting multiple animals simultaneously.3
How Can I Recognize Strangles?
The first signs of strangles are often nonspecific. Typically, the disease begins with a high fever, which can reach up to 104°F. At the same time, affected horses show apathy, appearing unusually calm or unresponsive, and eat poorly.4
As the disease progresses, more distinct symptoms appear. These include:
- Purulent nasal discharge
- Coughing
- Swollen lymph nodes in the head area, especially under the jaw or at the throat latch
The duration of the illness usually ranges from five to 14 days, but can vary. In addition to typical courses, atypical or severe courses are possible. In rare cases, complications such as abscesses in other body regions, fever reactions, or muscle problems can occur.
How a Veterinarian Diagnoses Strangles
Suspected strangles or any symptoms should always be clarified by a veterinarian as soon as possible. Since the disease is highly contagious, it is recommended to isolate affected horses early. Various samples are taken for diagnosis. These include swab samples from abscesses or the nasal-pharyngeal area, as well as lavage samples from the guttural pouch.
The examination of guttural pouch lavage samples is considered particularly reliable. Depending on the symptoms, an endoscopy may also be necessary. This involves using a small camera to examine the upper respiratory tract for visible changes.
Can Strangles Be Treated?
The treatment of strangles depends on the severity of the infection. In uncomplicated cases, hospitalization is often not necessary. The horse can recover under veterinary supervision in the stable, but must be strictly separated from other horses.
It is important to maintain hygiene measures to prevent further spread. The specific measures required depend on the conditions in the respective stable and are determined by the veterinarian.
In severe cases, such as infection of the guttural pouch or complications, hospitalization may be necessary. The guttural pouch is then flushed with an endoscope to remove pus. Treatment is individually tailored to the affected horse.
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Prognosis for a Strangles Infection
In most cases, strangles is uncomplicated, and the prognosis is good. Even with involvement of the guttural pouch, the prognosis is generally favorable, although treatment is more complex and may take longer.
In rare cases, severe courses occur. These include, for example, abscesses in internal organs, specific fever reactions, or muscle diseases. In such situations, the prognosis is cautious to unfavorable. Occasionally, the disease can also be fatal, although this is rare.
Can Strangles Be Prevented?
So far, strangles in horses is not a reportable or notifiable disease. The most important preventive measure is to avoid infection. Since strangles is very easily transmitted, hygiene and management in the stable play a central role.5
This includes:
- Consistent isolation of sick horses and possibly affected individuals
- Thorough cleaning and disinfection of equipment and stable areas
- Avoiding shared use of items like waterers or feed troughs in case of illness (especially in open stabling)
Vaccination is generally possible but offers only short-term protection of about three months. Additionally, you cannot vaccinate your animal if there are acute cases at the stable. This option is therefore only suitable in certain situations—such as with new arrivals or at competitions. It is also important to note that recovered horses can still be contagious weeks after symptoms have subsided or can still transmit strangles as silent carriers.