Strangles (Streptococcus equi) in Horses: A Complete Guide

Overview

Strangles is one of the most common and highly contagious bacterial infections affecting horses worldwide. Caused by Streptococcus equi subspecies equi, this respiratory disease gets its dramatic name from the characteristic swelling of lymph nodes in the throat area, which can become so severe that affected horses may experience difficulty breathing or "strangling" sounds.

While strangles can affect horses of any age, young horses between 1-5 years old are most susceptible, particularly those with developing immune systems or those experiencing stress from weaning, training, or transport. The disease spreads rapidly through horse populations, making it a significant concern for boarding facilities, training barns, and show circuits.

Despite its intimidating name and symptoms, strangles has a relatively good prognosis when properly managed. Most horses recover completely with appropriate veterinary care, though complications can arise if the infection spreads beyond the typical lymph nodes.

Causes

Strangles is caused exclusively by Streptococcus equi subspecies equi, a gram-positive bacterium that has evolved specifically to infect horses. This pathogen is highly adapted to its equine hosts and can survive in the environment for extended periods, making it particularly challenging to control.

The bacteria primarily targets the upper respiratory tract and associated lymphoid tissues. Once infected, horses can shed the bacteria through nasal discharge and pus from ruptured lymph nodes for weeks or even months. Some horses become chronic carriers, harboring the bacteria in their guttural pouches (air-filled chambers connected to the middle ear) and intermittently shedding the organism without showing clinical signs.

Transmission occurs through several routes:

• Direct contact with infected horses
• Contaminated water sources, feed buckets, and equipment
• Airborne droplets from coughing or sneezing
• Contaminated hands, clothing, and equipment of caretakers
• Shared grooming tools, bits, and halters

Symptoms & Signs

Early Stage Symptoms

The incubation period for strangles typically ranges from 3-14 days after exposure. Early signs often resemble a common cold and may include:

• Fever (often 102-106°F)
• Loss of appetite and depression
• Clear nasal discharge that gradually becomes thick and purulent
• Mild coughing
• Reluctance to lower the head to eat or drink
• Slight swelling of lymph nodes under the jaw

Progressive Symptoms

As the infection advances, typically within 7-10 days, more characteristic signs develop:

• Significant swelling of submandibular and retropharyngeal lymph nodes
• Thick, creamy yellow or white nasal discharge
• Difficulty swallowing (dysphagia)
• Extended head and neck posture
• Loud breathing or snoring sounds
• Complete loss of appetite
• The horse may stand with its head extended and appear anxious

Advanced Stage

In the final stage, typically 2-4 weeks after initial infection:

• Lymph nodes may rupture, draining large amounts of thick pus
• Fever often subsides once drainage begins
• Gradual improvement in appetite and attitude
• Continued drainage for several days to weeks

Complications

While most cases follow the typical course, complications can occur:

• Bastard strangles: Infection spreads to unusual lymph node locations
• Purpura hemorrhagica: Immune-mediated vasculitis causing swelling and bleeding
• Guttural pouch empyema: Infection of the guttural pouches
• Metastatic abscesses: Abscesses in internal organs
• Pneumonia: Secondary bacterial pneumonia

Diagnosis

Diagnosing strangles requires a combination of clinical examination and laboratory testing. Veterinarians will assess the horse's history, clinical signs, and perform specific diagnostic tests.

Clinical Examination

Your veterinarian will perform a thorough physical examination, paying particular attention to:

• Temperature and vital signs
• Lymph node palpation
• Respiratory assessment
• Nasal discharge characteristics
• Overall body condition and hydration status

Laboratory Testing

Bacterial Culture: The gold standard for diagnosis involves collecting samples from nasal discharge or abscess material for bacterial culture. This test can take 48-72 hours but provides definitive identification.

PCR Testing: Polymerase chain reaction testing offers rapid results (often same-day) and high sensitivity for detecting S. equi DNA.

Serology: Blood tests measuring antibodies can help identify exposure but may not distinguish between active infection and previous exposure.

Endoscopy: In some cases, veterinarians may use an endoscope to examine the upper respiratory tract and guttural pouches.

Treatment Options

Veterinary Treatment

Treatment of strangles requires careful veterinary management, as inappropriate antibiotic use can sometimes worsen the condition or lead to complications.

Antibiotic Therapy: The use of antibiotics in strangles is controversial and depends on the stage of infection. Early treatment with penicillin may prevent abscess formation, but antibiotics given during the abscess development stage may drive the infection deeper or cause bastard strangles.

Supportive Care: Most treatment focuses on supportive care:

• Anti-inflammatory medications (NSAIDs) to reduce fever and discomfort
• Soft, palatable feeds to encourage eating
• Fresh water available at chest height
• Hot packing of swollen lymph nodes to encourage drainage

Abscess Management: Once abscesses are mature, veterinarians may lance them to facilitate drainage and speed recovery.

Complications Management: Horses developing complications require intensive treatment, which may include:

• Intravenous antibiotics for bastard strangles
• Corticosteroids for purpura hemorrhagica
• Surgical drainage of guttural pouch infections

Supportive Care

Proper nursing care is crucial for recovery:

• Isolation from other horses
• Comfortable, well-ventilated housing
• Easy access to water and soft feeds
• Regular monitoring of temperature and appetite
• Gentle grooming and handling

Home Care

Important Note: Strangles requires veterinary supervision. Home care should only supplement professional treatment.

Isolation Protocols

• Isolate affected horses immediately
• Use dedicated equipment for infected horses
• Implement strict hygiene measures for caretakers
• Disinfect all surfaces and equipment regularly

Comfort Measures

• Provide soft, easily chewed feeds like soaked hay cubes or bran mashes
• Ensure fresh water is available at a comfortable height
• Apply warm compresses to swollen lymph nodes as directed by your veterinarian
• Monitor for changes in breathing, eating, or behavior

Environmental Management

• Maintain good ventilation while avoiding drafts
• Keep the environment clean and dry
• Remove and dispose of contaminated bedding properly
• Limit stress and maintain routine as much as possible

Prevention

Preventing strangles requires a multi-faceted approach combining biosecurity, vaccination, and management practices.

Biosecurity Measures

• Quarantine new horses for 21-28 days before introducing them to the herd
• Test new arrivals for strangles before mixing with resident horses
• Implement visitor restrictions during outbreaks
• Use dedicated equipment for each group of horses
• Regular disinfection of shared areas and equipment

Vaccination

Two types of strangles vaccines are available:

Intramuscular Vaccine: Traditional killed vaccine that provides moderate protection but may cause injection site reactions.

Intranasal Vaccine: Modified live vaccine administered into the nostrils, providing better local immunity with fewer side effects.

Vaccination protocols should be developed with your veterinarian based on risk factors and local disease prevalence.

Management Practices

• Maintain good general health through proper nutrition and parasite control
• Minimize stress from overcrowding, poor ventilation, or sudden changes
• Regular veterinary examinations and health monitoring
• Prompt isolation of horses showing respiratory signs
• Proper manure management and facility drainage

Prognosis & Recovery

The prognosis for uncomplicated strangles is generally excellent. Most horses recover completely within 4-6 weeks with appropriate care. Factors influencing recovery include:

• Age and overall health of the horse
• Promptness of diagnosis and treatment
• Development of complications
• Quality of nursing care
• Environmental conditions

Recovery Timeline

Week 1-2: Acute phase with fever, nasal discharge, and lymph node swelling Week 2-3: Abscess maturation and drainage Week 3-4: Gradual improvement in appetite and attitude Week 4-6: Return to normal activity levels Week 6-8: Complete resolution of discharge and lymph node swelling

Long-term Considerations

Most horses develop strong immunity after recovering from strangles and rarely become reinfected. However, some horses may become chronic carriers, requiring ongoing monitoring and management.

When to See a Vet

Immediate veterinary attention is required if your horse shows:

• Difficulty breathing or loud respiratory sounds
• Inability to eat or drink for more than 12 hours
• High fever (over 104°F) that doesn't respond to treatment
• Signs of severe depression or weakness
• Swelling that interferes with breathing or swallowing
• Any signs of complications like skin swelling or lameness

Emergency Situations

Seek emergency veterinary care immediately if:

• The horse cannot breathe normally
• Severe swelling blocks the airway
• The horse collapses or shows signs of shock
• Widespread skin swelling develops suddenly
• The horse shows signs of severe pain or distress

Conclusion

Strangles remains one of the most significant infectious diseases affecting horses worldwide. While the dramatic symptoms can be alarming, most horses recover completely with proper veterinary care and management. The key to successful outcomes lies in early recognition, appropriate treatment, strict isolation protocols, and comprehensive supportive care.

Prevention through biosecurity measures, vaccination programs, and good management practices remains the best approach to controlling this highly contagious disease. Horse owners should work closely with their veterinarians to develop comprehensive health management programs that include strangles prevention strategies appropriate for their specific situation.

Remember that every case of strangles is potentially serious and requires professional veterinary evaluation and ongoing monitoring throughout the course of the disease. With proper care, most horses return to full health and develop lasting immunity against future infections.