In my previous column, I discussed clostridial infections in the muscles of horses, most often following injections, that can lead to the disease known as malignant edema.
In addition to serious muscle infections, clostridial bacteria can also be an important cause of intestinal disease in foals and adult horses.
Two main species are involved, clostridium difficile (recently renamed clostridioides difficile) and clostridium perfringens.
Horses pick up the hardy clostridial spores from the environment and these grow in conditions that have no oxygen. Healthy animals also carry clostridium in their guts in low numbers without clinical disease and pass the bacteria in their feces.
Overgrowth of clostridial bacteria in the intestines can damage the lining tissue, creating severe inflammation and water secretion into the gut lumen, ultimately leading to severe, watery diarrhea. Damage to the gut lining also allows bacteria to enter the bloodstream, which may cause sepsis.
Just like the muscle disease, these bacteria in the gut are capable of producing lethal toxins that cause maximum tissue damage. Infections that occur in the small intestine are classified as enteritis, while those of the colon are called colitis. Clostridia bacteria can cause enterocolitis, infection of both the small intestine and colon.
The cause of clostridium overgrowth leading to disease is often difficult to determine. Abrupt food changes, stressful events such as shipping, mixing, surgery or competition and use of antibiotics are all thought to predispose horses to clostridial diarrhea. Outbreaks can occur, but it can also suddenly crop up in a single horse.
Horses with clostridial diarrhea (and diarrhea from other causes) are severely ill. Feces are copious, loose and may be blood-tinged. Affected horses may be extremely lethargic with signs of colic and abdominal swelling.
Horses may go off feed. Many have a fever, rapid heart rate and bright pink to red mucous membranes.
A veterinarian may pass a nasogastric tube during the clinical exam, which can generate a large volume of fluid from the stomach. This occurs because the bacteria stimulate secretions and also slow movement within the digestive system, creating a situation where a large volume of fluid remains in the stomach. Rectal examination and ultrasound (if available) often reveal loops of intestine that are distended and filled with fluid or gas. In very rapidly progressing cases, horses may simply be found dead.
Other causes of intestinal infection and inflammation can present similarly to clostridial enteritis including Salmonella infections. Diagnosis is based on clinical signs, detection of the clostridium bacteria in the feces or tissue based on bacterial culture and presence of toxins.
It can be especially tricky to confirm in horses that die of these infections because clostridia are one of many bacterial types that overgrow in the body after death. So, it can be a challenge to determine if the bacteria caused the disease or simply overgrew. In these cases, it is important to look for tissue changes consistent with the disease, as well as rule out the other common causes of intestinal inflammation. Detecting the presence of toxins is helpful to confirm the diagnosis.
The prognosis with clostridial diarrhea can be poor. Horses with diarrhea can be rapidly dehydrated and may require intravenous fluids with electrolytes. Anti-inflammatory medications such as flunixin and certain antibiotics are also used.
As serious as clostridium infections can be, there are no vaccines available for use in horses. Even though the spores are everywhere in the environment, good hygiene practices are important for control of a variety of infections and thus are a good idea.
For prevention in foals, it is essential that they ingest colostrum after birth to establish high levels of blood antibodies. The jury is still out whether or not animal-associated clostridium bacteria can be spread to humans, so good hand hygiene and limiting contact between sick horses and immunocompromised people is also a reasonable precaution.
For part one see “Wounds major cause of malignant edema,” March 5 edition page 71.
Dr. Jamie Rothenburger, DVM, MVetSc, PhD, DACVP, is a veterinarian who practises pathology and is an assistant professor at the University of Calgary’s Faculty of Veterinary Medicine. Twitter: @JRothenburger