What Is Strangles in Horses: Signs, Treatment & Prevention

What Is Strangles in Horses?

Strangles is a highly contagious bacterial infection that affects the upper respiratory system of horses. This disease is caused by the gram-positive bacterium Streptococcus equi equi, which invades the lymph nodes located around the throat and jaw. The condition earned its distinctive name due to the characteristic swelling of lymph nodes that can impede breathing and swallowing. While strangles shares some similarities with strep throat in humans, the manifestations in horses are considerably more dramatic, featuring pronounced lymph node abscesses and elevated fever. Understanding this disease is essential for horse owners, as it remains a reportable disease in many regions and requires immediate action to prevent widespread transmission within equine populations.

Understanding the Cause

The causative agent of strangles, Streptococcus equi equi, is a gram-positive bacterium that specifically targets horses and related equine species. This pathogen spreads through direct contact with infected horses or contaminated materials, making it exceptionally transmissible in environments where multiple horses are housed in close proximity. The bacteria colonize the upper respiratory tract and establish infection in the lymph nodes, triggering a robust inflammatory response from the horse’s immune system. This immune response, while ultimately beneficial for developing long-term immunity, manifests as the characteristic swelling, abscess formation, and systemic symptoms associated with the disease.

Recognizing the Symptoms of Strangles

The clinical presentation of strangles can vary significantly between individual horses, ranging from mild symptoms that may be mistaken for other respiratory conditions to severe manifestations requiring intensive care. Recognizing these signs early is crucial for timely isolation and treatment.

Primary Clinical Signs

Within 24 to 48 hours of the initial fever spike, horses typically exhibit characteristic symptoms including:

• Fever, often one of the first and most reliable indicators of infection
• Mucoid to mucopurulent nasal discharge, typically thick and yellow or purulent in appearance
• Depression and lethargy
• Loss of appetite and difficulty eating
• Cough
• Swelling of the lymph nodes (glands) under the jaw or at the throatlatch
• Submandibular lymphadenopathy with or without abscessation
• Abscesses that rupture and drain purulent material

Advanced or Complicated Symptoms

Horses with retropharyngeal lymph node involvement may experience more severe respiratory compromise, including:

• Difficulty swallowing (dysphagia)
• Inspiratory respiratory noise and breathing difficulty (dyspnea)
• Extended head and neck posture
• Severe airway obstruction in extreme cases

It is important to note that some horses exhibit only mild nasal discharge initially, which may be mistaken for less serious respiratory diseases. However, if fever is present, strangles should be considered a possibility and appropriate diagnostic measures should be undertaken.

Diagnosis of Strangles

Accurate diagnosis of strangles is essential for confirming the infection and implementing appropriate biosecurity measures. Diagnosis relies on multiple methods depending on the stage of infection and clinical presentation.

Diagnostic Methods

Veterinarians may employ several diagnostic approaches:

• Culture and PCR testing: Samples obtained from abscess material, guttural pouch washes, or nasopharyngeal swabs can be cultured or analyzed using polymerase chain reaction (PCR) to identify Streptococcus equi equi
• Endoscopy: In complicated cases, endoscopy of the upper respiratory tract may be required to visualize the extent of infection and abscess formation
• Ultrasound and radiographs: These imaging techniques help identify the location and extent of abscesses, particularly when internal abscesses are suspected
• Serology testing: Blood tests can detect antibodies to Streptococcus equi equi, though this is more useful for identifying persistent infections or carrier status
• Temperature monitoring: Measuring body temperature during quarantine provides early indication of rising temperatures that precede other clinical signs

Treatment Options for Strangles

Treatment approaches for strangles depend on the severity of the infection and whether complications are present. The primary focus is on supporting the horse’s immune response while managing symptoms and preventing secondary infections.

Supportive Care

In most cases, strangles is treated with rest and supportive care rather than aggressive antimicrobial therapy. This approach includes:

• Warm, dry environment: Providing a dust-free stall with good ventilation
• Palatable nutrition: Offering wet, sloppy feed from the floor to encourage eating and facilitate drainage of abscesses
• Hydration: Ensuring adequate water intake, which may be achieved through offering water with feed or using a soaker
• NSAIDs: Nonsteroidal anti-inflammatory drugs are used to decrease swelling, manage pain, and encourage appetite
• Hot compress therapy: Applying warm compresses to swollen lymph nodes to facilitate maturation and drainage of abscesses
• Topical treatments: Application of ichthammol to encourage abscess drainage
• Abscess flushing: Once abscesses rupture, flushing with povidone-iodine solution promotes proper drainage and healing

Antimicrobial Treatment

While controversial, antibiotics may be beneficial in specific circumstances. Antimicrobial treatment is indicated for:

• Cases with dyspnea (difficulty breathing)
• Cases with dysphagia (difficulty swallowing)
• Prolonged high fever
• Severe lethargy or anorexia
• Complicated manifestations including metastatic strangles, purpura hemorrhagica, or myositis

If antimicrobial treatment is warranted, procaine penicillin (22,000 IU/kg administered intramuscularly every 12 hours) is the antimicrobial of choice. However, it is important to note that antibiotics administered in early stages may prevent abscess formation but can occasionally prolong the disease course. When not treated with antibiotics, approximately 75% of horses mount a sufficient immune response to develop long-term immunity to strangles.

Prognosis and Recovery

The prognosis for uncomplicated strangles is generally excellent. Most horses recover completely within 2 to 4 weeks with appropriate supportive care and management. Horses typically make a full recovery and develop robust long-term immunity to the disease.

However, approximately 10% of horses affected in a strangles outbreak develop persistent infection due to failure of guttural pouch drainage, leading to recurrent cases of disease. These persistent carriers require special diagnostic protocols and targeted treatment to resolve the chronic infection.

Isolation and Quarantine Procedures

Proper isolation and quarantine are critical components of strangles management. If an outbreak occurs, implementing a comprehensive biosecurity control program is essential.

Immediate Isolation Measures

When strangles is suspected or confirmed:

• Isolate infected horses: Horses with temperatures of 38.5°C or above should be separated from others without clinical signs
• Physical separation: Use a double layer of electric fencing to eliminate nose-to-nose contact and prevent sharing of drinking water
• Halt all movement: Cessation of horse movement on or off the yard should continue until all cases and exposed horses are confirmed negative
• Dedicated caregiving: Use separate staff or dedicated caregivers to minimize contact between infected and non-infected horses
• Equipment segregation: Avoid sharing tack, grooming tools, feed buckets, and water troughs between horses

Prevention Strategies

Preventing strangles outbreaks requires a multi-faceted approach combining vaccination, biosecurity measures, and careful management of new arrivals.

Vaccination

Two types of strangles vaccines are available:

• Live attenuated vaccine: Administered by submucosal injection into the upper lip
• Multicomponent fusion protein vaccine: Administered via intramuscular injection

Both vaccines are indicated to reduce the severity of clinical signs and the formation of abscesses following exposure to Streptococcus equi equi. While not 100% effective, vaccination can help reduce disease severity and lower transmission rates. However, it is important to note that vaccines may be associated with complications, including vaccine-associated disease. A study demonstrated a 74% reduction in the number of foals that developed strangles following deliberate exposure when vaccinated.

Biosecurity and New Horse Screening

Reducing exposure of resident horses to Streptococcus equi equi is an effective control method. Key biosecurity measures include:

• Quarantine new arrivals: Isolate any new horse entering the barn for at least 2 to 3 weeks before joining the herd
• Pre-arrival screening: Test new horses prior to or following arrival to screen for disease
• Temperature monitoring: Monitor body temperature of horses in quarantine or returning from equestrian events for early detection of rising temperatures
• Strict hygiene practices: Regularly disinfect stalls, equipment, and water troughs
• Feed and water management: Provide separate feed and water sources to minimize disease transmission

Distinguishing Strangles from Other Equine Respiratory Diseases

Strangles shares some clinical features with other equine respiratory diseases, which can complicate diagnosis. Understanding the distinguishing characteristics is important for accurate identification:

Frequently Asked Questions

Q: Can humans contract strangles from infected horses?

A: No, strangles is a horse-specific disease. Streptococcus equi equi is adapted to equine hosts and does not infect humans. However, proper hygiene practices should always be maintained when handling infected horses.

Q: How long does strangles typically last?

A: Uncomplicated strangles typically resolves within 2 to 4 weeks with appropriate supportive care. However, some horses may experience prolonged recovery, and approximately 10% develop persistent infections.

Q: Is strangles fatal?

A: While strangles can be severe, it is rarely fatal in otherwise healthy horses when managed appropriately. Fatalities are more likely in complicated cases with severe airway obstruction or secondary complications.

Q: Can a horse get strangles more than once?

A: Horses that recover from strangles typically develop long-term immunity to the disease. However, horses with persistent infections that were never fully cleared may experience recurrent clinical signs.

Q: Should I always use antibiotics to treat strangles?

A: No. Antibiotics are reserved for complicated cases or when specific clinical indicators suggest their use. In uncomplicated cases, supportive care allows the horse’s immune system to develop natural immunity.

Q: How can I prevent strangles in my barn?

A: Prevention involves vaccination, strict quarantine protocols for new arrivals, rigorous biosecurity practices including regular disinfection, and careful management of horses returning from shows or events.

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medha deb

 

Medha Deb is an editor with a master's degree in Applied Linguistics from the University of Hyderabad. She believes that her qualification has helped her develop a deep understanding of language and its application in various contexts.

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