Bacterial diseases

My Horse Has Swollen Lymph Nodes

Josie F. Turner
By Josie F. Turner, Journalist specialized in Animal Welfare. Updated: March 21, 2024
My Horse Has Swollen Lymph Nodes

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Petting our horses is not only a way to improve our bond, it is a vital responsibility to look after their health. We may run our hand under their jaw because they enjoy it, but we also do so to check for any swelling in the lymph nodes. There are various causes of swollen lymph nodes in horses, but one of the most common (especially in young horses) is a disease called equine distemper, commonly known as the strangles.

In this article on my horse has swollen lymph nodes, AnimalWised looks at the reasons you can feel inflammation under the horse's jaw. In particular, we look at strangles in horses by revealing the causes, symptoms and treatment options available.

You may also be interested in: Abscess on a Dog's Gum - Causes and Treatment
  1. Why does my horse have swollen lymph nodes?
  2. What is strangles in horses?
  3. Causes of strangles in horses
  4. How is strangles in horses spread?
  5. Symptoms of strangles in horses
  6. Diagnosis of strangles in horses
  7. Treating strangles in horses

Why does my horse have swollen lymph nodes?

Horses have two major sets of lymph nodes which can be felt under the jaw. The submandibular lymph nodes are the closest, but there is a set known as the retropharyngeal lymph nodes which are closer to the throat. We can feel them if we press, but it should be obvious if they are swollen. You should notice because they feel different, not only larger, but harder.

Causes of swollen lymph nodes in horses include:

  • Parotiditis: this is a swelling of the salivary glands. When these swell, they are sometimes referred to as grass mumps.
  • Neoplasm: whether a benign cyst or malign cancer, it is possible we can find a neoplasm on one or more lymph node.
  • Other infection: if the horse has an infectious disease, it can cause the lymph nodes to swell.
  • Trauma: if the area around the lymph nodes has received physical trauma, they can swell.
  • Equine distemper: also known as strangles, we explain more below.

What is strangles in horses?

Strangles is an upper respiratory tract disease in horses. It mainly affects the retropharyngeal lymph nodes which can be found just below the mandible. It is a highly contagious disease which affects all equine animals, characterized by swollen lymph nodes. Abscesses can form and become purulent, but the swelling is the most obvious. The swelling causes the horse to have respiratory problems, the reason why it is referred to as strangles.

Fortunately, strangles in horses has a relatively low mortality rate. It usually does not exceed 2-3% of affected individuals. It has an incubation period of up to 8 days between infection and the first appearance of clinical symptoms.

All equidae can suffer from strangles, but horses are more susceptible than mules or donkeys. It is a common disease of horses in young animals between the ages of 4 months and 2 years. Horses under 4 months don't tend to get it because immunity from their mother's colostrum. Horses up to 2 years don't often have enough antibodies due to incomplete vaccination schedules.

Causes of strangles in horses

Horse strangles is caused by bacteria of the genus Streptococcus, specifically Streptococcus equi, subspecies Equi. On occasion, this bacterium can be associated with S. equi, subspecies Zooepidermicus.

After developing the disease, 75% of horses develop long-lasting immunity. However, animals affected by this pathology can remain permanently infected within the guttural pouch (diverticula of the Eustachian tubes that connect the inner ear with the larynx). They can secrete the bacteria with nasal exudate or saliva for months or years, all without showing symptoms, but spreading infections to other horses.

How is strangles in horses spread?

Equine mumps can be spread directly or indirectly. Direct contagion occurs through contact with a sick animal or an asymptomatic carrier. Indirect contagion occurs through:

  • Water (in which the bacteria can last 4 to 8 weeks)
  • Feeders, troughs and dispensers contaminated by the bacteria
  • Respiratory spray
  • Hands of caregivers or veterinarians

There are certain conditions that promote the spread of strangles. These include when equine animals of different origin mix, overcrowding in stables, cold winter temperatures, poor ventilation, reduced physical activity and vitamin deficiencies.

Symptoms of strangles in horses

Although we know that swollen lymph nodes are a symptom of strangles, this only occurs at certain stages of the disease. Additionally, symptoms will vary according to the type of strangles in horses. The two types of strangles in horses are:

  • Classical strangles
  • Bastard strangles

Classical strangles in horses

In 80% of cases, the disease follows the classic course where the bacteria enter through the nostrils. They then reach the tonsils to cause the inflammation. Afterwards, they pass to the regional lymph nodes (both submandibular and retropharyngeal) and pus forms within days. Since the pus is encapsulated in the lymph tissue, abscesses form.

In the last phase of classical strangles, the lymph nodes soften as they finally drain. This will occur as a fistula through the submandibular area. In some cases, solid pus (chondroids) forms in the guttural pouches and can accumulate to form an empyema.

To better understand this whole process, the clinical signs that the horse presents with classical strangles are:

  • First phase: fever (103.1-105.8 ºF/39.5-41 ºC), anorexia, apathy, depression, inflammation of the nasal and oral mucosa.
  • Second phase: decrease in fever, coughing, runny nose, swollen lymph nodes becoming hot, hard and painful, pharyngitis leading to a loss of appetite due to the pain it causes.
  • Third phase: fever returns, pus discharge from nose and mouth, lymph nodes become soft, diffuse and not painful, chondroids and empyema of the guttural bags.

Horses normally recover after this process, but sometimes there are complications such as:

  • Sinusitis due to bacterial colonization of the paranasal sinuses.
  • Pneumonia due to aspiration of pus when swallowing.
  • Compression asphyxia of the larynx and pharynx if the inflammation is severe.
  • Laryngeal hemiplegia due to compression of the recurrent laryngeal nerve due to the inflammatory process.
  • Affects other lymph nodes such as intestinal (mesenteric), chest (mediastinal), prescapular and cervical.

Bastard strangles in horses

However, in the remaining 20%, the process is not limited to the area that we have discussed. It can pass via blood or lymph nodes to other lymph nodes and organs (including lung, liver, kidney, spleen, mesentery and brain). Once there, the bacteria will form abscesses. It can also target the muscles, skin, reproductive system or produce reactions mediated by the horse's immune system. This form is known as bastard strangles, where the horse can manifest:

  • Abscesses in various organs: lung, liver, intestine, spleen, kidney, brain.
  • Mastitis or inflammation of the mammary glands due to infection from the foal to the mother during lactation.
  • Cutaneous lump due to accumulation of fluid on the head, giving them the appearance of a ‘hippopotamus head’.
  • Reproductive disorders.
  • Dermal disorders.
  • Immune - mediated reactions: haemorrhagic strangles (inflammation mucous membranes hemorrhage), myositis (muscle infarction and progressive atrophy) and/or glomerulonephritis (inflammation of the renal glomerulus through which urine is filtered).

Diagnosis of strangles in horses

Mumps in horses can be diagnosed through different diagnostic tests, as we will see below:

Differential diagnosis

Due to their respiratory symptoms, equine distemper can be confused with the following conditions in horses:

  • Rhodococcus equi: affects young animals from 1 to 6 months of age producing, among other things, suppurative pneumonia.
  • Influenza or equine flu.
  • Equine herpesvirus (type 1 and 4) because they produce respiratory symptoms.
  • Secondary infections due to E. equi zooepidermicus, causing respiratory issues and inflammation of the uterine endometrium.

Clinical diagnosis

Strangles is suspected if a horse, especially under two years of age, has respiratory symptoms with clear inflammation of the submandibular region. This is especially if they have been in close contact with other horses, even if they do not show symptoms since they can be contagious and asymptomatic at the same time.

Laboratory diagnostics

The diagnosis of strangles in horses is confirmed by taking samples and sending them to the laboratory where bacterial tests will be carried. These samples can be:

  • Pus from abscesses
  • Nasal swabs
  • Nasal, tracheobronchial or guttural pouch washes

The laboratory tests that diagnose the disease are:

  • SAB
  • PCR
My Horse Has Swollen Lymph Nodes - Diagnosis of strangles in horses

Treating strangles in horses

The treatment of equine distemper will depend on different factors, such as the type of strangles. Likewise, other factors need to be taken into account to help the animal overcome the disease.

Specific treatment

The specific or etiological treatment is intended to kill the bacteria that cause the disease. In this way, depending on the type of mumps it causes, the treatment will be as follows:

  • Treatment of classical strangles: beta-lactam antibiotics such as penicillin are mainly used, being effective in the acute phase when abscesses have not yet appeared. When these have already appeared, it is advisable to use heat and drain the lymph nodes, only using antibiotics in severe cases.
  • Treatment of bastard strangles: abscesses should be drained and antibiotics given intravenously over a long period of time.

Symptomatic treatment

To treat the symptoms that equine mumps can produce, the following will be used:

  • Anti-inflammatories such as flunixin meglubine, phenylbutazone, or meloxicam.
  • Antipyretics to lower fever (e.g. methinazole).
  • Corticosteroids or antiendotoxic drugs such as dexamethasone or pentoxicillin for hemorrhagic strangles.
  • Fluid therapy.

Hygienic-sanitary treatment

This consists of applying a series of measures to reduce the concentration of bacteria in the horse's environment. This will help the horse recover, prevent reinfection and stop the spread to other animals. Measures which need to be taken include:

  • Isolation of the animal
  • Keep their area clean
  • Temperature control
  • Rest
  • Soften their food
  • Keep food at a proper height to avoid strain
  • Vitamins or supplements to boost immunity

Surgical treatment

Sometimes abscesses need to be removed as follows:

  1. Use of hot cloths to soften them.
  2. Shave the area.
  3. Cleaning and disinfection.
  4. Incision in the declining area of the abscess.
  5. Drainage and washing.
  6. Disinfection with chlorhexidine or povidone iodine.
  7. Disinfection with antibiotics and give anti-inflammatory drugs for 10 days.

In cases of suffocation or severe difficulty in breathing, an emergency tracheostomy (incision in the windpipe) should be performed.

These processes can only be carried out by a trained equine veterinarian. You should never try to drain an abscess or perform a tracheostomy on your own because you could worsen the clinical picture. Therefore, if you observe any of the symptoms mentioned above and suspect that your horse may have strangles, do not hesitate to call a professional.

This article is purely informative. AnimalWised does not have the authority to prescribe any veterinary treatment or create a diagnosis. We invite you to take your pet to the veterinarian if they are suffering from any condition or pain.

If you want to read similar articles to My Horse Has Swollen Lymph Nodes, we recommend you visit our Bacterial diseases category.

  • Aguilar, J. J., Pelassa, A. (2012). Infectious Diseases of Equines. Spanish Academic Editorial.
  • Prescott, J. Equine Strangles, Comprehensive Equine Veterinary Study. Available at:
  • Ruíz de León, M. A. (2002). Diseases of the respiratory system of the horse. Veterinary World. Available at:
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My Horse Has Swollen Lymph Nodes