What is Malignant Edema?
Clostridial spores are found in the air, dirt, and even in your horse’s intestines. They can be introduced into your horse’s skin just by inoculation. Most often, clostridial spores are able to infiltrate your horse’s tissues through a puncture wound or injury that breaks the skin. Since it is impossible to see these bacteria, it is common for infection to be caused by a hypodermic needle during inoculation or drawing blood. The bacteria may have been on the skin or hair already before the injection, which is why it is important to thoroughly clean the area with alcohol before injection. The symptoms of malignant edema move rapidly, so it is essential that you seek treatment for your horse right away if you even suspect this condition.
Malignant edema (clostridial myositis) is an uncommon and life-threatening condition caused from the infection of the tissues by the clostridial bacteria. Many times, malignant edema is caused by an injection of an irritating material, especially flunixin (banamine), inferior injection method, or an infected lesion. Intramuscular injections have a higher instance of causing malignant edema. It is believed that the clostridial bacteria may be introduced through the injection. Clostridial bacteria create dangerous toxic materials that damage and kill the tissues, which produces the perfect environment for fast growth of the bacteria. These are very strong toxins that will cause shock and death if treatment is not received right away.
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Symptoms of Malignant Edema in Horses
Some of the most commonly reported signs of malignant edema include:
- Painful, hot, and swollen muscles that continue swelling
- High body temperature
- Loss of appetite
- Rapid heart rate
- Air pockets under the skin
- High respiratory rate
Causes of Malignant Edema in Horses
There are many possible causes of malignant edema, but the most common are:
- Infected wound
- Injections of certain irritating substances (dipyrone, B vitamins, dewormers, phenylbutazone, and antihistamines)
- Poor injection method
- Complication from castration
Diagnosis of Malignant Edema in Horses
To diagnose your horse, the veterinarian will first need to take a complete history and immunization record information. In addition, tell the veterinarian what symptoms you have noticed, when they started, and what happened prior to the beginning of the symptoms. Also, let the veterinarian know if you have given your horse any medications in the past 24 hours. Next is the physical examination, which usually starts with the veterinarian studying your horse from a distance, evaluating attitude, conformation, stature, and behavior. After, the veterinarian will check your horse’s body from head to tail, checking skin for lesions, redness, inflammation, and edema. A detailed check-up is done next including body temperature, blood pressure, height, weight, respiration and heart rates, breath sounds, and reflexes. The veterinarian will also palpate the abdomen and chest to listen with a stethoscope for any abnormalities. A sample will be taken from any lesion by making a small incision and using a sterile cotton swab, which is then mixed with a substance that is placed in a petri dish and allowed to grow. This will not only verify the presence of the bacteria, but it will also help in determining which antibiotic will make the most effective treatment. In addition, a fine needle aspirate will be retrieved and examined microscopically.
Blood tests necessary in diagnosing malignant edema are fungal and bacterial cultures, chemistry panel, complete blood count (CBC), and blood urea nitrogen (BUN). Finding sphero echinocytes or echinocytes in the blood smears can aid in diagnosing anemia caused by the clostridial bacteria. Gram stains can find gram-positive rods before a culture can read positive. Ultrasound and other imaging need to be used to find the pockets of gas and fluid so the veterinarian is able to treat them all. This is essential to successful treatment because if just one small abscess is missed, it will be a fatal mistake.
Treatment of Malignant Edema in Horses
Your horse’s treatment begins with releasing the fluid and gas from the infected tissues and providing high doses of intravenous (IV) antibiotics and other medications.
To help the wounds heal, they need oxygen, so the veterinarian will make deep incisions with drains placed for draining the fluids and gas. This usually needs several large incisions down to the muscle.
Your veterinarian will be using an aggressive treatment plan with a high dosage of intravenous (IV) antibiotics such as penicillin, oxytetracycline, or metronidazole. Fluids and oxygen may be given as well to prevent shock. In addition, nonsteroidal anti-inflammatory drugs (NSAIDS) and pain relievers should be given for pain and inflammation.
Your horse will definitely need to be hospitalized for 7-10 days for treatment and observation. Continuing the IV antibiotic is extremely important to your horse’s survival.
Recovery of Malignant Edema in Horses
Unfortunately, even with all of this treatment, the prognosis is guarded. The survival rate with malignant edema is only about 40% even with treatment. This is a strong bacteria that is hard to kill.