# Strangles (Streptococcus equi infection) in Horses
Overview
Strangles is one of the most common and highly contagious bacterial infections affecting horses worldwide. Caused by the bacterium Streptococcus equi subspecies equi, this disease primarily targets the upper respiratory tract and associated lymph nodes. The name "strangles" comes from the characteristic difficulty breathing that affected horses experience due to severely swollen lymph nodes that can obstruct the airway.
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, transport, or environmental changes. The disease spreads rapidly through horse populations, making it a significant concern for stables, breeding facilities, and equestrian events.
Despite its alarming symptoms, strangles typically has a good prognosis when properly managed. However, complications can arise if the infection spreads beyond the typical lymph nodes, leading to a more serious condition called "bastard strangles." Early recognition and appropriate veterinary care are crucial for successful treatment and preventing spread to other horses.
Causes
Strangles is caused exclusively by Streptococcus equi subspecies equi, a highly specialized bacterial pathogen that has evolved specifically to infect horses. This gram-positive bacterium is remarkably hardy and can survive in the environment for extended periods, making it particularly challenging to control.
The bacteria primarily spread through direct horse-to-horse contact via respiratory droplets produced when infected horses cough, sneeze, or breathe heavily. However, transmission can also occur through:
- Contaminated water sources, feed buckets, and shared equipment
- Nasal discharge on surfaces, handlers' clothing, or grooming tools
- Airborne droplets traveling short distances between stalls
- Asymptomatic carrier horses that harbor bacteria in their guttural pouches
The bacteria have a particular affinity for the lymphoid tissue in the horse's head and neck region. Once introduced into the nasal passages or mouth, the bacteria quickly colonize the nasopharynx and begin multiplying. The horse's immune system responds by sending white blood cells to the regional lymph nodes, causing the characteristic swelling and abscess formation that defines strangles.
Environmental factors such as overcrowding, poor ventilation, stress, and inadequate hygiene practices significantly increase the risk of transmission and outbreak severity.
Symptoms & Signs
Early Symptoms
The incubation period for strangles typically ranges from 3-14 days after exposure. Early signs often resemble a common cold and may include:
- Mild fever (101-103°F)
- Clear nasal discharge that gradually becomes thick and purulent
- Decreased appetite and energy levels
- Mild depression or lethargy
- Slight swelling of lymph nodes under the jaw
- Occasional coughing
Advanced Symptoms
As the infection progresses, typically within 7-10 days, symptoms become more pronounced:
- High fever (103-106°F)
- Thick, creamy yellow or white nasal discharge from both nostrils
- Severe swelling of submandibular and retropharyngeal lymph nodes
- Difficulty swallowing (dysphagia)
- Extended head and neck posture to ease breathing
- Loud breathing sounds or stridor
- Complete loss of appetite
- Formation of hot, painful abscesses in the throat region
Emergency Signs
Certain symptoms require immediate veterinary attention as they indicate potential life-threatening complications:
- Severe respiratory distress or open-mouth breathing
- Blue-tinged gums or tongue (cyanosis)
- Inability to swallow water or saliva
- Collapse or extreme weakness
- Signs of "bastard strangles" including abdominal pain, neurological symptoms, or abscesses in unusual locations
- Sudden worsening of condition after initial improvement
Diagnosis
Accurate diagnosis of strangles requires a combination of clinical examination and laboratory testing. Veterinarians typically employ several diagnostic approaches:
Clinical Examination: The characteristic combination of fever, nasal discharge, and swollen lymph nodes often provides a strong clinical suspicion of strangles.
Bacterial Culture: The gold standard for diagnosis involves collecting samples of nasal discharge or abscess material for bacterial culture and identification. This method confirms the presence of S. equi and allows for antibiotic sensitivity testing.
PCR Testing: Polymerase chain reaction (PCR) tests can rapidly detect S. equi DNA from nasal swabs or wash samples. This method is faster than culture but doesn't provide antibiotic sensitivity information.
Serology: Blood tests measuring antibodies against S. equi can help identify exposure but cannot distinguish between active infection and previous exposure or vaccination.
Guttural Pouch Endoscopy: In cases where carrier status is suspected, endoscopic examination of the guttural pouches may reveal bacterial accumulation.
Ultrasound: Can help evaluate lymph node involvement and identify abscesses ready for drainage.
Early and accurate diagnosis is crucial not only for appropriate treatment but also for implementing proper quarantine measures to prevent spread to other horses.
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 active abscess development can drive the infection deeper, leading to bastard strangles. Commonly used antibiotics include:
- Penicillin (procaine or benzathine)
- Trimethoprim-sulfamethoxazole
- Ceftiofur
- Rifampin (for resistant cases)
Abscess Management: Mature abscesses are typically allowed to rupture naturally or are surgically drained when ready. Hot compresses may help promote maturation and drainage.
Anti-inflammatory Medications: Non-steroidal anti-inflammatory drugs (NSAIDs) like phenylbutazone or flunixin meglumine help reduce fever, pain, and inflammation.
Supportive Care: IV fluids may be necessary for dehydrated horses or those unable to drink normally.
Surgical Options
Surgical intervention may be necessary in severe cases:
- Tracheostomy: Emergency airway management if lymph node swelling severely compromises breathing
- Abscess drainage: Surgical drainage of mature abscesses to promote healing
- Guttural pouch lavage: For persistent carriers with guttural pouch infections
Home Care
While veterinary supervision is essential, supportive home care plays a crucial role in recovery:
Isolation: Immediately isolate affected horses to prevent spread. Maintain strict quarantine protocols for at least 4-6 weeks after clinical recovery.
Environmental Management: Provide a clean, well-ventilated, dust-free environment. Soft bedding helps comfort horses that may lie down more frequently.
Nutrition: Offer palatable, easy-to-swallow feeds such as soaked hay cubes, bran mashes, or pelleted feeds. Ensure constant access to fresh, clean water.
Monitoring: Check temperature twice daily and monitor for changes in appetite, breathing, or lymph node swelling.
Gentle Exercise: Light hand-walking may be beneficial once fever subsides, but avoid strenuous exercise until fully recovered.
Hygiene: Maintain strict hygiene protocols when handling affected horses, including dedicated equipment and clothing changes.
Prevention
Preventing strangles requires a multi-faceted approach focusing on biosecurity, vaccination, and management practices:
Quarantine Protocols: Isolate new horses for 2-3 weeks before introducing them to the herd. Test new arrivals with nasal swabs or blood work.
Vaccination: Strangles vaccines are available but have limitations. Discuss vaccination strategies with your veterinarian based on your specific risk factors.
Biosecurity Measures:
- Avoid sharing water buckets, feed containers, and grooming equipment
- Disinfect stalls, trailers, and equipment regularly
- Limit horse-to-horse contact at events
- Maintain visitor logs and restrict access during outbreaks
Environmental Management: Ensure good ventilation, avoid overcrowding, and minimize stress factors that can compromise immune function.
Regular Health Monitoring: Implement routine health checks and temperature monitoring, especially during high-risk periods.
Prognosis & Recovery
The prognosis for uncomplicated strangles is generally excellent, with most horses making a complete recovery within 4-6 weeks. However, several factors influence the outcome:
Favorable Factors:
- Early recognition and appropriate care
- Young, otherwise healthy horses
- Uncomplicated cases with typical lymph node involvement
- Proper supportive care and nutrition
Complications That May Worsen Prognosis:
- Development of bastard strangles (internal abscesses)
- Secondary pneumonia
- Purpura hemorrhagica (immune-mediated vasculitis)
- Guttural pouch empyema leading to carrier status
Most horses develop strong immunity following natural infection, with reinfection being uncommon. However, approximately 10% of horses may become asymptomatic carriers, harboring bacteria in their guttural pouches and potentially spreading infection to naive horses.
When to See a Vet
Immediate veterinary attention is required if you observe:
- Any combination of fever, nasal discharge, and swollen lymph nodes
- Difficulty breathing or abnormal respiratory sounds
- Inability to eat or drink normally
- Severe depression or weakness
- Signs of complications such as neurological symptoms or abdominal pain
- Any horse showing illness in a facility with a known strangles outbreak
Early veterinary intervention significantly improves outcomes and helps prevent spread to other horses. Never attempt to treat suspected strangles without professional guidance, as inappropriate treatment can lead to serious complications.
Remember that strangles is a reportable disease in some jurisdictions, and veterinary diagnosis is essential for proper outbreak management and prevention of further spread within the equine community.