Intramuscular Injections and Clostridial Myonecrosis
Clostridial myonecrosis (also called clostridial myositis or gas gangrene) is a very serious infection caused by growth of Clostridium bacteria in muscle. Clostridia are anaerobic spore-forming bacteria, meaning they only grow in environments without oxygen and they can stay dormant in the form of very tough (e.g. difficult to kill) 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 injections (e.g. vaccines, medications), surgery or trauma.
If clostridial spores are in a muscle and an anaerobic (oxygen-free) environment is created, they can start to grow. An anaerobic environment may form if the muscle is significantly damaged, such as from intramuscular injection of an irritating drug, or serious trauma. When the spores start to grow, they can cause very serious infection. Various clostridial species can be involved, but Clostridium perfringens is most common. Regardless of the particular species, 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 immediate and aggressive care, but is often fatal even with treatment. One of the most important (and dramatic) aspects of treatment is opening up the infected area to provide drainage and allow air (and oxygen) to enter the tissues. Large incisions need to be made into the muscle (this procedure is known as a fasciotomy). While this can look horrific, it's a critical aspect of treatment. High doses of antibiotics are also needed, along with other supportive care.
Fortunately, clostridial myonecrosis is relatively uncommon. Avoiding this disease involves decreasing the chances of creating the anaerobic environment in which clostridial spores can grow:
- Intramuscular injection of irritating substances should be avoided. Flunixin meglumine (also called Banamine and a few other trade names) 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 veterinarian should be contacted promptly, especially if the size of the affected area is rapidly expanding.
- There is no evidence that any pre-injection techniques (e.g. swabbing the area with alcohol) have any influence on the occurence of this disease. 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's an option) because of the intensive care that is required. Aggressive and expensive treatment is needed. The prognosis is already guarded, but if optimal treatment isn't started promptly, the prognosis is very poor.
More information about clostridial myonecrosis is available on the equIDblog Resources page.
