Strangles in Horses

Strangles is a common bacterial infection that causes outbreaks on numerous horse farms each year. The disease is highly contagious, and can rapidly spread to any in-contact horses.

Although most horses recover uneventfully, there is a risk of serious complications such as bastard strangles. Horses showing symptoms of strangles require immediate veterinary attention to confirm the diagnosis and set up appropriate quarantine and biosecurity protocols.

Most horses develop minor infections with strangles. In some cases, enlargement of the lymph nodes can cause difficulty eating or breathing.

Strangles infection has several common complications that can develop in some horses.

The guttural pouches, an extension of a horse’s respiratory tract near the back of the head, can become infected with the bacteria in some cases. This results in one of two conditions: guttural pouch empyema or chondroids. Guttural pouch empyema is when the guttural pouches become filled with pus. Over time, the pus can harden into solid masses, called chondroids. In both of these conditions, horses will continue to shed bacteria in their nasal secretions even after other symptoms have resolved.

Bastard strangles is when the infection spreads from the lymph nodes of the head to other parts of the body, such as the lungs, liver, spleen, kidney, or brain. The symptoms of this infection depend on the organ affected. In severe cases, bastard strangles can lead to organ failure and require extensive treatment.

Purpura hemorrhagica occurs when a horse is exposed to strangles a second time, after previously recovering from an infection. This second exposure can be from another infectious exposure or vaccination. The immune system is strongly stimulated against the bacteria, and causes damage to normal tissues in its attempt to clear the bacteria. Symptoms include:

Severe swelling of the head, body, and limbs Red spots on the gums

Purpura hemorrhagica is an emergency, and requires immediate veterinary attention if the condition is suspected.

The causative agent of strangles is Streptococcus equi equi, a bacteria that spreads between horses through direct contact with infected horses or contaminated equipment. After inhalation, the bacteria infects the lymph nodes under and behind the jaw, causing the severe swelling that is characteristic of the disease.

Strangles is usually suspected based on symptoms displayed on physical examination. Other diagnostic tests to confirm include:

• Blood work
• Nasal or lymph node swabs to identify the bacteria
• Blood work to identify antibodies against the bacteria
• Endoscopy of the guttural pouch
• X-rays of the guttural pouch
• Ultrasound of the abdomen to identify bastard strangles

Treatment primarily focuses on reducing symptoms while the immune system fights the bacteria. Symptomatic care can include:

• Hot-packing the lymph nodes
• Flushing burst lymph nodes with antibacterial solutions
• Anti-inflammatory medications
• In severe cases, administering antibiotics to help reduce bacterial load
• Tracheostomy in horses struggling to breathe

Horses diagnosed with strangles must be isolated from all other horses, with strict biosecurity measures to prevent spread to other horses.

Horses with strangles must be isolated long-term. At a minimum, horses must be isolated until their symptoms resolve. Follow-up testing 3 weeks later is highly recommended to identify any horses still shedding bacteria. Most horses with strangles recover uneventfully with no long-term effects. Horses with severe complications, such as bastard strangles or purpura hemorrhagica, have a guarded prognosis even with aggressive treatment.

Horses that continue to have nasal discharge after 2 weeks of supportive care may have guttural pouch empyema or chondroids. These horses require further treatment, such as flushing the guttural pouches with antibiotic solutions, to remove the contaminated material.

Prevention of strangles involves biosecurity measures whenever horses are exposed to other horses. Strategies for prevention include:

• Quarantining new arrivals for 3 weeks, while monitoring for signs of disease
• Testing new horses for strangles carrier status before introducing them to farms
• Vaccination of high-risk horses, such as those attending shows or events

The strangles vaccines that are available are effective at reducing the severity of symptoms, but are not entirely preventative. Horses previously infected with strangles are at risk of developing purpura hemorrhagica if vaccinated.

Strangles is common and causes numerous outbreaks on horse farms each year.

• Supportive care including anti-inflammatory medications
• Antibiotics
• Tracheostomy