Strep-Related Myopathies in Horses by a Vet – 2025 Strangles Complication & Muscle Disease Guide 💉🐴
In this article
Strep-Related Myopathies in Horses by a Vet – 2025 Strangles Complication & Muscle Disease Guide 💉🐴
By Dr Duncan Houston, BVSc
Introduction
Strangles, caused by Streptococcus equi, is typically a mild upper respiratory disease in horses—but in rare cases, it can trigger life-threatening muscle-related complications. These immune-mediated myopathies range from severe muscle damage and toxic shock-like syndromes to purpura hemorrhagica and rapid muscle wasting. In 2025, early recognition and aggressive veterinary intervention remain essential to saving affected horses.
Typical Strangles Infection 🧬
- Caused by Strep equi bacteria
- Common in young horses under 5 years
- Symptoms:
- Nasal discharge
- Fever
- Swollen lymph nodes, especially under the jaw
Rare Complication: Immune-Mediated Myopathy ⚠️
- Occurs during or shortly after strangles
- Causes widespread muscle inflammation and damage
- Believed to resemble toxic shock syndrome in humans
Clinical Signs
- Stiff, stilted gait
- Swollen or painful back and hindquarter muscles
- Reluctance or inability to rise
- Rapid deterioration over a few days
Prognosis is poor—many horses do not survive even with intensive treatment.
Treatment Approach 💊
- Antibiotics: typically penicillin
- Anti-inflammatories: NSAIDs for pain and inflammation
- Corticosteroids: to suppress immune-mediated damage
- IV fluids: to support circulation and kidney function
Unfortunately, most horses do not respond to therapy once muscle breakdown is severe.
Another Complication: Purpura Hemorrhagica 🩸
- Occurs after recovery from strangles
- Caused by an immune reaction to Strep equi antigens
- Leads to vasculitis (blood vessel inflammation)
Clinical Signs
- Swelling of limbs and body
- Stiff, painful muscles
- Fever and depression
- Colic signs due to decreased blood supply to the gut
Rapid Muscle Atrophy 🧩
- Another immune-mediated syndrome
- Muscles over the back, shoulders, and hindquarters shrink rapidly
- Often seen in the weeks after respiratory symptoms resolve
Diagnosis
- History of recent strangles
- Muscle enzyme blood tests (elevated CK, AST)
- Muscle biopsy may confirm inflammation and necrosis
Preventing Severe Complications 🛡️
- Ensure proper treatment and recovery monitoring in strangles cases
- Do not vaccinate during an active infection
- In exposed horses, a blood titer can predict risk of vaccine reaction
Case Example: Toxic Shock Myopathy in a Mare
- 6-year-old mare developed strangles with nasal discharge and mild fever
- Five days later, she became extremely stiff and could not rise
- Muscle enzymes were elevated; IV fluids and antibiotics started
- Despite treatment, her condition deteriorated, and euthanasia was required
FAQs About Strep-Related Myopathies
Q: Can strangles cause permanent damage?
A: Yes. In rare cases, it causes irreversible muscle loss, severe immune disease, or death.
Q: Should I vaccinate after a recent strangles outbreak?
A: Wait several weeks and perform a blood titer first. Some horses may overreact to the vaccine.
Q: Is purpura hemorrhagica contagious?
A: No—it’s an immune reaction, not an infection. However, the original strangles infection is contagious.
Conclusion
Strangles is usually mild, but in rare cases it can trigger devastating muscle complications. These immune responses may lead to widespread muscle breakdown, vasculitis, colic, or irreversible atrophy. In 2025, horse owners must act quickly when muscle stiffness, weakness, or unusual pain appears during or after a respiratory illness. Early vet intervention is critical—even though prognosis is often poor, fast treatment offers the best chance for survival.
Need help diagnosing or managing a post-strangles complication? Visit AskAVet.com or download our app 📱 to consult with Dr Duncan Houston for emergency care guidance. 🩺🐴
