Strangles is a disease every horse owner should be familiar with and know about. This highly contagious bacterial infection, caused by Streptococcus equi, can affect horses of any age or breed and spreads surprisingly fast. Whether through direct contact with infected horses, shared equipment, or even people unknowingly acting as carriers, Strangles can quickly become a serious concern.
Recognizing the symptoms early — such as nasal discharge, swollen lymph nodes, and fever — is crucial for preventing severe complications and reducing the spread to other horses. Implementing quarantine protocols, practicing strict biosecurity and preventive care measures, and understanding the options for prevention and treatment are essential for managing outbreaks effectively.
By staying informed and proactive, horse owners can help protect their animals and others in the equine community from the potential risks of Strangles.
What Is Strangles in Horses, and What Causes It?
‘Strangles’ is a term used for an upper respiratory infection in horses caused by the bacteria Streptococcus equi. The most common clinical signs seen in a horse infected with the Strangles bacteria include nasal discharge, enlarged lymph nodes under the jaw or along the throat, coughing, fever, and/or trouble swallowing. It is not uncommon for the enlarged lymph nodes to eventually rupture and drain pus. This is a normal progression of the disease. When lymph nodes become severely enlarged, they can compress the airway, which is where the term “Strangle” comes from. This is a relatively uncommon occurrence with infections.
What Are The First Signs Of Strangles In Horses?
Horses, uniquely, have two large outpouchings from their pharynx, known as the guttural pouches. These pouches, whose purpose remains a mystery, unfortunately, can fill with pus from lymph nodes in the case of Strangles. This often results in an abundance of nasal discharge. In most cases, the pus will drain out of the guttural pouches as a sick horse recovers from the infection. However, there are some horses where the pus doesn’t drain and becomes a solid structure known as a chondroid. These horses, known as “silent carriers,” may appear to have completely recovered from a Strangles infection, but could still be harboring this contagious pus/chondroid in his/her guttural pouches. Even though these horses appear healthy, they can be the cause of outbreaks in herds of horses. The only way to determine if a horse is a silent carrier is to test or perform an endoscopy of the guttural pouches.
Strangles is very contagious, which means a horse that has the infection can very easily give it to other horses they come in contact with. The pus/drainage from the nose or lymph nodes is what can infect another horse. Humans and barn equipment can also act as fomites. A fomite is an object that comes in contact with the bacteria and then unknowingly transfers it to another place or horse. So if a horse with Strangles sneezes on your jacket, then your jacket could potentially give Strangles to another horse! It is very important that horses infected with Strangles are quarantined or isolated from other horses and that you continually practice good biosecurity.
Although the most common presentation for Strangles is the upper respiratory infection as described above, other, more severe forms of the disease can occur, albeit quite rarely. They are as follows:
- Pneumonia: In some cases, the upper respiratory infection can lead to a lower airway infection. These horses tend to become a lot sicker and require more aggressive treatment.
- Purpura hemorrhagica (PH): Uncommonly, horses will have a hypersensitivity reaction towards the Strangles infection OR the Strangles vaccine. This results in inflammation of the vessels throughout the whole body (vasculitis). These horses will develop severe, painful swelling of the limbs along with edema/swelling of other systems. Horses affected by PH will typically be very ill and require intensive care. The most severe forms of PH may warrant humane euthanasia.
- Bastard Strangles: This is a condition where the Strangles infection travels to locations outside the respiratory tract. The most common location for Bastard Strangles (also known as a metastatic infection) to occur is in the abdomen. Horses may develop abscesses that result in chronic weight loss, fever, or colic. These infections can be very difficult to treat, and in many cases, humane euthanasia is recommended.
Diagnosing Strangles in Horses
Procedure for Streptococcus Equi Testing
For Strangles testing, a nasal swab should only be used if a horse has purulent (pus) nasal discharge. Otherwise, a nasopharyngeal wash or guttural pouch lavage is needed to effectively test a horse for Strangles. These two diagnosis techniques make use of lab work to correctly identify a Strangles infection in horses.
Nasopharyngeal Wash
A nasopharyngeal wash, also known as a nasal pharyngeal lavage, is a diagnostic procedure for horses, that involves flushing the nasal passages and pharynx with a saline solution to collect a sample of the fluids and cells present, thus making it a useful tool for horse owners and veterinarians when trying to diagnose strangles in horses.
How a Nasopharyngeal Wash Is Done: The horse is sedated. A 22” pipette is passed through the nasal passage to the back of the throat (nasopharynx). Sterile saline is then infused through the pipette to wash the area of the throat. This saline is then caught in a cup as it drains from the nostrils. What is caught in the cup is the sample that will be sent to the laboratory.
Guttural Pouch Wash
A Guttural Pouch Wash (GPW) is a diagnostic procedure for horses, specifically designed to collect a sample from the guttural pouches. These pouches are air-filled cavities located in the head, connected to the Eustachian tube and the nasal passages.
How a Guttural Pouch Wash: In general, there are two different methods for guttural pouch testing.
- The horse is sedated. A video endoscope is passed through the nasal passage and guided into the guttural pouch (please be aware the horse has a left and right guttural pouch). Once in the guttural pouch, the veterinarian can observe for any signs of infection. Then sterile saline is infused into the pouch and then either aspirated back through the endoscope OR caught in a cup (we use a red solo cup) as it drains out the pouch and through the nostril. This is performed for both the left AND right guttural pouches. What is caught in the cup is the sample that will be sent to the laboratory.
- The horse is sedated. A device with video monitoring is passed up the nasal passage so that the nasopharynx and openings to the guttural pouches can be observed (the video monitoring device does not have the ability to get into the guttural pouches). A 22” pipette is then passed through the opposite nasal passage to the back of the throat (nasopharynx). The video monitoring device is then used to guide the pipette into the guttural pouch and confirm its placement. Once in the guttural pouch, sterile saline is infused and caught in a cup once it drains from the pouch and through the nostrils. This is performed for both the left AND right guttural pouches. What is caught in the cup is the sample that will be sent to the laboratory.
The sample that is submitted to the laboratory is tested for the Streptococcus equi bacteria using a PCR test. This tests for the bacteria’s DNA. The PCR test is favored over culture because Streptococcus equi will not reliably grow in culture. PCR testing is also much faster, and results may be available in 1-2 days of testing.
These same tests are used to clear a horse of infection and therefore release him/her from quarantine. In many cases, horses will show clinical resolution in 1-2 weeks after the onset of clinical signs. Clinical resolution means the horse no longer has a snotty nose, fever, big lymph nodes, or cough. However, horses can continue to shed the bacteria for weeks beyond clinical resolution. So this means that even if your horse appears to have cleared the infection, they could still be at risk of infecting other horses for up to 6 weeks after infection, sometimes longer. As discussed above, horses have also become “silent carriers.”
When it comes to determining if a horse could still be infectious/spreading to other horses, the type of test matters. A horse requires three consecutive negative nasopharyngeal washes to be cleared of a strangles infection. This is because horses can harbor the infection within their guttural pouches and only intermittently shed from the pouches. Therefore, one negative test may just indicate that you have missed the intermittent shedding from the pouch. A horse requires one negative guttural pouch wash to be cleared of a strangles infection.
Understanding these testing requirements is crucial for horse owners to ensure the health of their horses and prevent the spread of Strangles.
Treatment Options for Horses with Strangles
For Horses Displaying “Classic” Clinical Signs
As mentioned, Strangles most commonly presents as an upper respiratory infection - snotty nose, enlarged draining lymph nodes, coughing, and/or fever. We typically recommend supportive care for these cases – NSAIDs (Banamine) for fevers, foods that are easy to swallow, and cleaning of draining lymph nodes. Although it is a bacterial infection, we ideally do not treat it with antibiotics. Antibiotics can sometimes prolong the infection (how long your horse is sick) and interfere with a horse’s natural immune response.
Horses that recover from a Strangles infection will have years of good natural immunity against the Strangles bacteria, which means it’s very unlikely that a horse will get reinfected. But if you give antibiotics, this period of natural immunity will be significantly reduced. There are some other serious concerns about antibiotics in horses. Antibiotics can put a horse at risk for colitis (diarrhea). In healthy horses, there is a lot of natural flora (bacteria) in the gut that helps with digestion and health. Antibiotics can disrupt this flora and cause an overgrowth of bad bacteria, leading to colitis. Colitis in horses can be a very serious, life-threatening condition. Therefore, we only want to use antibiotics when necessary.
Complicated Cases
Horses that suffer from one of the previously mentioned complications (pneumonia, PH, Bastard Strangles) may require more aggressive therapy and, oftentimes, antibiotics. Antibiotics are used in these cases because the body needs help in controlling/eliminating the bacteria. These cases will typically require a thorough evaluation by your veterinarian and possibly hospitalization.
How Can Equine Strangles Be Prevented?
There are Strangles vaccines available. These vaccines can be helpful in protecting your horse from strangles, but they are not guaranteed to prevent infection. As previously mentioned, the immunity developed after a natural infection is in some ways better than vaccination and likely to be protective against reinfection for years.
Strangles infections are transmitted from horse to horse. So, vaccination may be recommended for horses that are often interacting with new or different horses, such as at a show or competition. Because vaccination may not prevent disease, it is important to practice other biosecurity measures, especially when interacting with new/unknown horses. If introducing a new horse to your herd/facility, the new horse is ideally quarantined for a period of time and monitored for signs of illness before allowing the new horse to interact with others. If traveling to a show or competition, avoid nose-to-nose contact with other horses, avoid sharing barn equipment or water buckets, and disinfect any shared equipment or space.
Partner With a Veterinarian for Better Protection Against Strangles in Horses
Strangles is very infectious and can spread through populations of horses in shared spaces – making it crucial for owners to recognize symptoms and take appropriate quarantine and care actions. What starts as a small concern can quickly spread through an entire barn.
As we discussed, in most cases, horses will have a snotty nose, fever, draining lymph nodes and/or cough and then recover within a period of weeks. It is important to ensure your horse is appropriately tested before clearing him/her from quarantine. If you’re concerned your horse has a Strangles infection, it is important to involve your veterinarian. A veterinarian can provide the best plan for you and your horse, ensuring the most effective management of Strangles.
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