Strangles in Horses

If you own or work with horses, it is important to know what strangles is, how to recognize it and what diagnosis and treatment entail. Strangles is a bacterial infection caused by Streptococcus equi var. equi (simply referred to as S. equi). The condition, also called equine distemper, is highly contagious, but most horses recover fully with early intervention and treatment under a veterinarian's guidance.

Key Takeaways

• Strangles is caused by Streptococcus equi var. equi (S. equi), and it spreads through direct contact between infected horses, shared equipment and contaminated feed and water sources.

• Fever is typically the first symptom, appearing within 3 days of exposure, followed by nasal discharge and swollen lymph nodes.

• A veterinarian must diagnose and oversee all treatment, as horses can continue shedding the bacteria for up to 6 weeks after symptoms appear to be resolved. 

• Vaccination is an important preventive tool, though it does not guarantee full immunity and works best when combined with strong quarantine practices.

What Is Strangles in Horses?

Streptococcus equi var. equi (S. equi) is the bacterium responsible for strangles, a pathogen (disease-causing organism) that targets the upper respiratory tract and lymph nodes. Equine strangles is one of the most frequently diagnosed infectious diseases of horses worldwide, with the first written record dating back to 1251. Strangles most commonly occurs in horses that are in regular contact with other animals and under the age of 2, but horses of all ages are at risk. 

The bacteria travel through direct nose-to-nose contact, shared equipment and feeding and watering stations. Once inhaled or ingested, S. equi crosses the mucous membrane lining of the nose and throat and enters the bloodstream. It then settles into the lymph nodes, where it multiplies and triggers abscesses (pockets of infected fluid) to form. As those abscesses grow, they can put pressure on the trachea, making it hard for the horse to breathe normally and causing the horse to stretch its neck.

The concerning sound caused by difficulty breathing and dysphagia (trouble swallowing) is where equine strangles gets its name. In severe enough cases, the condition can be fatal due to suffocation, though this is not common. On rare occasions, abscesses form in the abdomen, brain or other organs, rather than the jaw. Called bastard strangles, this complication can produce abdominal pain or neurological signs, such as circling and an unsteady hind end. The severity of the disease and the onset of complications vary greatly, with the horse’s immune system having a major role in the outcome.  

Expert tip: A horse can look and act recovered while still carrying S. equi and shedding it from their body into the surrounding environment. These asymptomatic carriers have no visible signs of illness but can still infect other horses. Therefore, confirmed negative test results should be required before a recovered horse is cleared to rejoin the herd.

What Are the Signs and Symptoms of Equine Strangles?

Most horses with strangles show similar signs, but more severe symptoms can develop, particularly in younger horses. Recognizing the symptoms early is crucial to prevent the spread of bacteria and ensure proper care, so be on the lookout for the following:

Elevated Body Temperature

Within 2 to 3 days of exposure, fever appears. A reading above 101.5 degrees Fahrenheit generally indicates fever and is reason to isolate the horse and call your veterinarian immediately. However, while the normal resting range is typically 99-101.5 degrees Fahrenheit, it is recommended to know your individual horse's baseline, as even 1 degree above that baseline warrants veterinary attention, regardless of whether the reading falls within the general normal range. Other symptoms may not have developed yet at this stage, but acting early gives the vet the most to work with in terms of treatment options. 

Runny Nose and Nasal Secretions

Nasal discharge follows the fever in the coming days. It starts clear, then thickens into a yellowish fluid as the infection advances. As an important clarification, nasal discharge alone does not confirm strangles; respiratory infections and allergies can look similar, and your veterinarian will need to test your horse before arriving at a diagnosis. 

Swollen Lymph Nodes

Swelling of the lymph nodes under the jaw (submandibular) and around the throat (retropharyngeal) occurs as bacteria multiply. These nodes can become large, firm and painful, sometimes forming abscesses that may rupture and drain pus. Strangles abscesses typically rupture between 1 and 4 weeks after the initial infection.

Low Energy and Reduced Interest in Feed

Lethargy and reduced appetite develop as the infection progresses. In more advanced cases, the swollen lymph nodes compress the trachea enough to cause visibly labored breathing accompanied by strangling sounds. 

Expert tip: If you notice symptoms and suspect strangles in your horse, it is best to isolate it until vet evaluation. This helps to stop the bacteria from spreading to other horses if there is a positive diagnosis.

How Do Veterinarians Diagnose Strangles?

In most cases, veterinarians can confirm a strangles diagnosis based on the combination of fever, nasal discharge and swollen lymph nodes. However, a definitive diagnosis requires more advanced diagnostic techniques, including laboratory testing. 

A culture swab, also called a nasal swab, is standard for testing equine strangles. The swab is swiped along the inside of the nostril to pick up any bacteria present. Results come back in roughly 2 to 3 days, but they may be inconclusive or a false positive, particularly if only small amounts of nasal discharge are available or if it is early in the disease progression. 

A nasal wash or guttural pouch lavage is another common technique. By way of a small tube, saline passes through the nasal passages or into the guttural pouch (two large, air-filled structures near the throat), then exits the nose and is collected for analysis. Polymerase chain reaction (PCR) testing identifies bacterial DNA directly and returns results faster, and fine needle aspiration of swollen lymph nodes can confirm which bacteria are present at the site. In some cases, blood samples may also be collected to check for an elevated level of fibrinogen (glycoprotein essential for blood clot formation and wound healing), which suggests a strangles infection.

Expert tip: Jot down when each symptom appears, and take your horse's temperature before your veterinarian arrives, to know its baseline temperature. Even a rough timeline and whether the horse has a true fever (temporary increase in normal body temperature) give the vet a clearer starting point for identifying the infection and determining when and where exposure likely occurred.

How Do You Treat Strangles in Horses?

Strangles treatment centers on supportive care, keeping the horse stable, and managing symptoms through medication administered by a veterinarian while the infection runs its course. There is no single treatment that clears strangles outright, so your vet may recommend a combination of the following: 

Supportive Care and Quarantine

Stall rest in a quarantined space away from healthy animals is the foundation for treatment and recovery. The infected horse needs to stay hydrated and eat regularly. The horse should be closely monitored for any sign of systemic spread or worsening respiratory distress.

Anti-Inflammatory Medication

Flunixin meglumine (Banamine®) and phenylbutazone (VetOne® vetriBute™ bolus) are non-steroidal anti-inflammatory drugs (NSAID). It is commonly used to reduce fever and maintain appetite in horses during recovery. No medication should be given without direct veterinary guidance.

Wound Care and Drainage

When lymph node abscesses form, a veterinarian may apply warm compresses to encourage them to mature and open. After rupture, the site is flushed with sterile saline to clear bacteria and limit the risk of further spread. 

Tracheostomy

If lymph node swelling compresses the airway significantly, a temporary tracheostomy may be required. This is a procedure in which a breathing tube is placed directly into the trachea to restore airflow. This is a clinical procedure that should only be performed by veterinary professionals. 

Antibiotics

Antibiotics are not automatically part of a strangles treatment plan. Whether they are appropriate depends on how severe the case is and where the infection stands; that determination belongs to the veterinarian, rather than following a standard protocol. In select cases, Trimethoprim-Sulfamethoxazole, an oral antibiotic option, is prescribed. 

Guttural Pouch Lavage

In horses that remain clinical for more than 2 weeks, guttural pouch examination is recommended to assess for significant empyema (a condition characterized by a collection of pus). It is then determined whether lavage is needed to wash out pus and chondroids (hardened pus balls) from the guttural pouch. Repeated lavage may be needed because it can be difficult to clear all purulent material. In some cases, additional treatment is given after lavage, such as Penicillin G injectable (norbrook® norocillin, penicillin G Procaine Injectable Solution) into the guttural pouch.

Expert tip: After symptoms resolve through treatment, your vet will likely want to confirm the horse is no longer shedding the bacteria. The vet may perform guttural pouch lavage or PCR testing before advising you to remove the horse from isolation. 

How Can You Prevent Strangles in Horses?

Strangles prevention typically involves a combination of the following: 

Vaccination

Two vaccines for strangles are available in the United States, including:

• Pinnacle® I.N. (Zoetis): This is a modified live intranasal vaccine administered into one nostril, with one primary dose followed by a second dose 2 to 3 weeks later and annual revaccination required. Pinnacle® I.N. is available by prescription through Tractor Supply’s horse pharmacy. The intranasal product stimulates mucosal immunity at the natural site of infection and is the more commonly used option. Do not use during an active outbreak.

• Killed (inactivated) intramuscular vaccine: This option can occasionally trigger abscess formation at the injection site. Consult your veterinarian about appropriate product selection via our horse pharmacy.

Neither vaccine provides complete protection, and vaccination should always be discussed with your veterinarian.  

Strangles vaccination is not recommended during an active outbreak or within two weeks of a confirmed exposure, as administration during active infection or recent exposure can trigger purpura hemorrhagica, a potentially severe or fatal immune-mediated condition. Horses with high antibody levels from recent natural infection or recovery are at particular risk. In situations where outbreak exposure is possible, consult your veterinarian before vaccinating. Pre-vaccination antibody titer testing may be recommended in some cases to identify horses at elevated risk. 

Caring Properly for Quarantined Horses

Horses quarantined while recovering from strangles should be tended to last each day, after all healthy horses in the barn have been cared for, to help prevent the spread of infectious bacteria. Grooming kits, tack and saddlery, which come in contact with a recovering horse, should not be used on any other animal without being thoroughly disinfected first. Also, disinfect stall and equipment surfaces with appropriate sprays and cleaners, wear disposable gloves and monitor temperatures twice daily with a digital thermometer during outbreaks. Empty stalls and spray down stall mats and stable equipment fully, machine-wash any nylon halters and disinfect all grooming materials after every use.

Expert tip: Certain environments, such as boarding and show facilities, raise exposure risk. You may want to consider dedicated equipment per horse, enforce limits on contact between horses and make a clear plan for isolating any horse that starts showing symptoms.

Frequently Asked Questions About Strangles in Horses

Can a horse fully recover from strangles?

Yes, most horses recover without lasting complications when veterinary-guided supportive care is followed. Horses that clear the infection also tend to develop natural immunity that holds for several years.

How long is a horse with strangles contagious?

Bacterial shedding can continue for up to 6 weeks after symptoms are resolved. Your veterinarian will use guttural pouch sampling to confirm the horse is clear before it returns to shared spaces.

Is nasal discharge always a sign of strangles?

No, respiratory infections and allergies produce similar discharge. Testing by a veterinarian is the only way to confirm whether strangles is the cause.

Find Strangles Solutions at Tractor Supply’s Horse Pharmacy

Strangles may be highly contagious amongst horses, but with early detection and veterinary guidance, the condition is highly manageable. While the name can sound alarming, most horses make a full recovery with proper care and patience. Tractor Supply’s horse pharmacy carries prescription medications and a wide range of horse supplies to support your veterinarian’s care plan.