Avoiding gas gangrene/clostridial myositis
October 14, 2016
Dr. Ray Randall, a semi-retired veterinarian in Bridger, Montana, says any time you give an injection of any sort, be aware of the possibility of adverse reaction such as clostridial myositis. He dealt with the situation more than 25 years ago and it left quite an impression.
I have pictures taken many years ago of a horse I treated in 1989 for a clostridial infection following a vaccination. He survived and lived about 15 more years. He was disfigured from the infection, but still functional, and was used as a lesson horse for a long time.
This horse was not very good about injections, and the owner gave it to him in the hindquarter (but not in the best location). This horse also had a history of reactions—not handling vaccinations very well.
It was a Friday when the owner called. The horse had received the vaccination early in the week. This horse always got stiff and sore after vaccination, and the owner had been doing some massage work on this horse. When they called me, I thought it didn’t sound good. I loaded up supplies and headed down look at that horse. When I walked into that barn I could smell the sickly sweet odor put off by clostridial organisms. The horse was standing out in the arena, holding his left hind leg up. The whole leg was cold and swollen, with gas bubbles under the skin.
I got him started on antibiotics, clipped his whole hind leg from hock to croup, and figured out where the major problem areas were. We cleaned those up and made a number of incisions to open them up, let the gas out, and start drainage. The tissues were dead and rotting. We didn’t have to use any anesthesia to make the incisions because he had no feeling at all. These were incisions 8 to 12 inches long.
We asked about possible euthanasia. The horse was insured for a fair amount of money and I told the owner that chances of surviving this infection were poor and it would be completely reasonable to euthanize him, but we’d have to call the insurance company first. The owner didn’t want to do that; he told me to save the horse if I could. So we got the horse loaded and took him to our clinic. He was already starting to feel better, just from the antibiotics and opening up those areas; you could tell by the way he acted.
We kept him about a month and he ended up sloughing an area in his left thigh that was as large as half a big watermelon. He had a hole where all the muscle was gone. His sciatic nerve kept functioning, however, and his hip joint was ok, so he survived and was able to keep going.
When a horse is exhibiting signs of colic, Banamine is often the bottle the owner reaches for. However, if the injection is given intramuscularly, the cure can be worse than the illness.
Intramuscular injections occasionally cause local abscesses if the needle or skin area was dirty when the injection is given. Sometimes abscesses occur even under very clean conditions. The worst kind of injection-induced infection is development of clostridial myositis, or myonecrosis, after an injection. The common term for this is gas gangrene.
This type of infection is caused by certain types of clostridial bacteria that are present in the environment, according to Dr. Liz Boos, an associate veterinarian at Belle Fourche Veterinary Clinic. Some of these bacteria commonly live in the horse's intestines and don't cause problems under normal conditions. They are present in manure, and form spores that last a very long time in the environment. Thus they are often on the horse's skin and can be taken into the tissues with an injection. These bacteria can be in a dormant state, and then multiply when conditions are right; they grow best in an environment without oxygen, such as bruised and damaged tissue with very little blood supply.
The dormant spores readily "come to life" and become dangerous when they encounter favorable conditions in which to multiply and start producing deadly toxins.
Different kinds of clostridia cause different diseases—like tetanus, malignant edema, blackleg in cattle, enterotoxemia in young calves and life-threatening gut infection and diarrhea in young foals.
Some types of injections seem more risky for clostridial infections. "One of the most common is flunixin meglumine (Banamine), if it is given in the muscle rather than in the vein," says Boos. "There is also some thought that this drug sets up an ideal pH in the tissues for these bacteria to grow in." A clostridial infection can happen with any kind of injection, but flunixin has been the most common culprit.
"Most people are familiar with Banamine, which is a trade name, but they need to be aware that there are also some generic flunixin products that are the same thing, and just as risky," says Boos.
Dr. Tia Nelson, DVM, from Helena, Montana, says many horse owners over the years have given Banamine and its generic equivalents via intramuscular injection to treat colic and other situations when a horse needs anti-inflammatory medication to reduce pain, fever and swelling. "Not every horse will have a problem with IM injections of Banamine (many do not) but it's not worth the risk," says Nelson.
"It doesn't happen every time. Many injections have been given without this problem occurring, but it is certainly associated with giving Banamine. It is always a risk," Boos says.
Originally, flunixin meglumine was labeled for intramuscular or intravenous (IV) administration, but now it is only labeled for IV injections, due to serious reactions and infections that have occurred with the intramuscular injections. "The drug company changed the label, so now it says 'to be administered via IV injection only.' There are many older bottles still around, however, that have labels stating it can be given either IV or IM," says Nelson.
"This drug does cause some muscle damage when injected into the muscle, and damaged tissue has less oxygen supply than healthy tissue," says Boos. "This creates an ideal environment for clostridial bacteria to proliferate. Horses tend to have a high amount of these clostridial bacteria in their environment so even if you are diligent in trying to have a clean area for the injection, a needle going through the skin may take in a few bacteria," she says.
"Irritation from the drug causes part of that muscle to die," says Boos. "Normally this is not a big deal, but it can set up an anaerobic environment which enables clostridia to thrive. It's not the bacteria themselves that cause the problem; it's the toxin that they secrete. When they multiply they produce toxins that damage the surrounding tissue even more, and produce gas. You can feel air bubbles under the skin. It feels crinkly, like bubble wrap," Boos says.
All the tissue around that area may die and slough off. If a horse gets an injection in the neck and then develops clostridial myositis, the whole side of the neck might eventually be affected and slough away. The necrotic area may spread up to the head and down to the shoulder. "The bacteria in this airless environment just keep multiplying and producing toxins unless you can open up these areas so they are exposed to oxygen in the air. This is why you see those horrific photos of horses with multiple slashes and drainage areas. Antibiotic therapy and anti-inflammatory medication is crucial for treatment, but it is even more important to expose those necrotic tissues to air," says Boos.
Boos recommends never giving flunixin products, like Banamine, intramuscularly. They can be given as an intravenous injection, or as an oral paste. The oral paste is what Boos suggests keeping around in case of colic. "In an emergency, the injectable form of Banamine can be given off label orally (squirted into the mouth)," she says.
The flunixin is readily absorbed from the gastrointestinal tract, which works about as fast as an intramuscular injection, but IV administration provides the fastest response—a major consideration in a horse with colic, Nelson says.
In situations where fast action is required, and you're not trained to give it via IV, Nelson suggests squirting it in the horse's mouth, rather than risking an intramuscular injection.
The liquid form is absorbed readily through the mucosal tissues of the mouth and probably is effective more quickly than the oral paste. However, it does irritate the mucosal tissues, so it may cause ulcers if given orally very frequently. "IV injection, by someone who knows how to do it, is the best route," says Boos. "Don't try it unless you know what you are doing, however, because if any of this solution leaks out of the vein you have another big problem."
If some of the drug slips out of the vein and into the surrounding tissue, it burns, damages and irritates that tissue, creating serious swelling and blocking the vein. "This may wreck the vein (ending up with jugular vein thrombosis), but that's not a life-threatening thing, compared with a clostridial infection that may kill your horse. Any time you can avoid a problem, it's better than trying to fix it afterward," Nelson says.
"If horse owners need to have some on hand, and are given a prescription for it, and are giving it at home, they need to be very confident in their ability at giving an IV injection. For most of my clients, the Banamine paste is much safer and simpler to have on hand, without the potential for this reaction," says Boos.
Horses can recover from the clostridial infection, but there can be quite a bit of scarring around the injection site, and it may affect the horse's performance.
Early on, when ivermection dewormers came out first as injectable products, there were instances of clostridial infections entering at the injection site.
"This is something to be aware of any time you give your horse an intramuscular injection. If there is extensive swelling or a crinkly feeling to the swollen tissue, the horse needs immediate medical attention. It may occur within the first day, or within a week or so after the injection. I would expect some obvious swelling within the first 24 hours, but it may take a little more time than that for the clostridial bacteria to produce toxins," says Boos.
"I have never given Banamine any route but IV," says Nelson. "That's what they taught me in vet school, 18 years ago, because that's the safest way to give it. I would never, under any circumstance, give it intramuscularly. A clostridial infection can kill the horse so quickly that you may not have time to deal with it until it's too late."