Clostridial myonecrosis (also called clostridial myositis or gas gangrene) is a very serious infection caused by growth of Clostridium bacterium in muscle. Clostridia are anaerobic sporeforming bacteria, meaning they only grow in environments without oxygen and they can stay dormant in the form of very tough spores. Clostridal spores can be found in healthy muscle. Presumably they enter the bloodstream periodically from the intestinal tract but aren't able to grow because of the presence of oxygen in healthy muscle. They lie dormant, waiting for the right conditions to start growing (which in most horses never occurs). Clostridial spores can also be introduced into muscle during vaccination, surgery or trauma.
If clostridial spores are in muscle (either residing there or introduced) and an anaerobic (oxygen-free) environment is created, they can start to grow. An anaerobic environment can be created following significant tissue damage from things such as intramuscular injection of irritating drugs or serious trauma. When these spores grow, they can cause very serious infection. Various clostridia can be involved, but Clostridium perfringens is most common. Regardless, infection is characterized by a very rapidly progression of soft tissue swelling, pain and systemic signs like fever and toxemia. The affected area can expand very quickly. Clostridia often produce gas when they grow and crepitus (a crackling feeling) can be felt over the infected area from the presence of gas in the tissues.
Clostridial myonecrosis is a life-threatening disease. It requires aggressive care, and is often fatal. One of the most important (and dramatic) aspects of treatment is opening up the infected area to provide drainage and allow air to enter. Large incisions need to be made into the muscle. While this can look horrific, it's a critical aspect of treatment. High doses of antibiotics are needed, along with other supportive care measures.
Fortunately, this is an uncommon disease. Avoiding it involves decreasing the chance of creating an appropriate environment for clostridial spore growth.
- Intramuscular injection of irritating substances should be avoided. Flunixin (Banamine) is commonly associated with this disease and should not be injected intramuscularly. Other irritating drugs include phenylbutazone (Bute) and ivermectin.
- Any muscle soreness or swelling that develops after an intramuscular injection should be taken seriously. A vet should be contacted promptly, especially if the size of the affected area is rapidly expanding.
- There is no evidence that any pre-injection techniques (i.e swabbing the coat with alcohol) have an influence of infection rates. Clostridial spores are resistant to alcohol, and most other disinfectants.
- If your horse has clostridial myonecrosis, it should be treated at an equine hospital if that is an option because of the intensity of care that is required. Aggressive and expensive treatment is needed. The prognosis is already guarded, and if optimal treatment isn't started promptly, the prognosis is very poor.