Definition

CDI is an inflammation of the small intestine, cecum, and large colon commonly resulting in diarrhea and varying degrees of toxemia.

Pathophysiology

Clostridium difficile is a Gram-positive spore-forming bacterium found in a small percentage of healthy adult horses, and a larger percentage of young healthy foals. It is acquired through ingestion of spores. The disease is hypothesized to occur from a disruption of the normal resident GI microbiota, often as a result of antimicrobial exposure. C. difficile produces 2 major toxins (A and B), a cytotoxin and an enterotoxin, that work synergistically. However, strains that only produce toxin B are capable of inducing disease. These toxins cause clinical signs by their direct toxic effects on the colon and through proinflammatory effects on neutrophils. The net result are varying degrees of fluid secretion, mucosal damage, and intestinal inflammation. Some strains of C. difficile also produce a binary toxin, but its role in equine enterocolitis is unknown.

Systems Affected

Incidence/Prevalence

It is usually sporadic, but outbreaks have been reported and are most common in foals on breeding farms.

Signalment

There is no reported breed, age, or sex predilection.

Signs

Causes

Risk Factors

Differential Diagnosis

CBC/Biochemistry/Urinalysis

Other Laboratory Tests

Imaging

The large colon contents may appear hypoechoic with increased motility and the intestinal wall may be thickened.

Other Diagnostic Procedures

Palpation per rectum to rule out another GI lesion.

Pathologic Findings

Gross abnormalities include fluid intestinal contents, and multifocal hemorrhagic or diffusely darker appearance of the serosal surface of the small and large intestines. More severe cases may have marked intestinal edema and hemorrhage, with petechiae and ecchymoses throughout. Histologically, depending on the severity, the small and large intestine may have mucosal necrosis, mucosal and/or submucosal thrombosis, hemorrhage, edema, congestion, neutrophilic infiltration, fibrinonecrotic pseudomembranes, and occasionally numerous Gram-positive rods on the superficial mucosa can be present.

Appropriate Health Care

Best managed intensively owing to the frequent need for aggressive fluid therapy and the high risk of secondary problems. If the diarrhea is not severe and adequate hydration can be maintained, treatment on farm could be attempted.

Nursing Care

IV fluid therapy with balanced polyionic electrolyte solution is the most important supportive treatment. Sodium bicarbonate may be required to correct a severe metabolic acidosis. In severely hypokalemic horses, 20–40 mEq/L of potassium chloride can be added to the IV fluids. IV administration of KCl should not exceed 0.5 mEq/kg/h. Oral supplementation with KCl (50 g every 6 or 8 h) is also effective to correct hypokalemia.

An oral electrolyte solution along with clean, fresh drinking water should be provided. Hypertonic saline (4–6 mL/kg IV of 5–7.5% NaCl) may be indicated in severely dehydrated animals. Feet should be iced for 72 h continuously in an attempt to prevent laminitis.

Activity

Animals should be handled accordingly and an isolated area should be used and disinfected appropriately because diarrheic horses are potentially infectious.

Diet

Free-choice hay, preferably in a hay net, because hypoproteinemic horses eating off the ground may develop severe facial edema. Large amounts of grain should be avoided due to the risk of further GI flora disruption.

Owing to the severe catabolic state that occurs in colitis, forced enteral feeding or partial or total parenteral nutrition may be required.

Client Education

Clients should be made aware of the potential for mortality and the serious risk of secondary problems such as laminitis and jugular vein thrombosis. They should also be warned that the horse should be considered infectious, and appropriate sanitation of contaminated areas should be recommended.

Surgical Considerations

N/A

Drug(s) of Choice

Contraindications

Metronidazole may be teratogenic and is therefore contraindicated in pregnant mares.

Precautions

Flunixin meglumine may be nephrotoxic in dehydrated animals. It may mask severe pain that indicates a surgical lesion, and should be used judiciously when the diagnosis is still in question.

Possible Interactions

Cimetidine should not be used concurrently with metronidazole because there is interaction through hepatic inhibition.

Alternative Drugs

N/A

Patient Monitoring

Frequent monitoring of hydration status, character and volume of diarrhea, and for presence of edema, and observe for signs of colic and laminitis.

Prevention/Avoidance

Antibiotics should be used judiciously to decrease the risk of disruption of the GI microflora.

Possible Complications

Expected Course and Prognosis

Mortality rates range from 10% to 40%; however, referral hospital-based studies are a biased population and the overall mortality rate is likely lower. Death can occur from the primary GI disease; however, euthanasia is often opted for due to cost of treatment, poor response to initial treatment, or development of severe laminitis. The prognosis is good when the diarrhea resolves shortly after presentation and no signs of laminitis occur.

Associated Conditions

Age-Related Factors

N/A

Zoonotic Potential

Some C. difficile strains found in horses are also found in people with CDI. While it is unknown whether horse–human transmission occurs, it is advisable to treat all affected horses as zoonotic risks.

Pregnancy/Fertility/Breeding

Metronidazole should not be administered to pregnant mares. An increased risk of abortion may be present due to endotoxemia and hypovolemic shock.

Synonyms

See Also

Laminitis

Abbreviations