Clostridia-associated Enterocolitis in Horses

Clostridium difficile and C perfringens have been implicated in this acute, sporadic disease of horses characterized by diarrhea and colic. Because of uncertainty about the etiology, the condition has also been referred to as idiopathic colitis, but there is now good evidence that these organisms are responsible for enterocolitis in horses. See also Clostridia-associated Enterocolitis.

Etiology:

C difficile is found only infrequently and C perfringens is found in low concentrations in the feces of normal horses. Both organisms may be present in soil or the environment and be ingested by horses. The factors that trigger disease are not well known, but it is presumed that some alteration in the normal flora permits excessive multiplication of the bacteria, which produce toxins capable of causing intestinal damage and systemic effects.

Predisposing factors that have been suggested include change in diet and antibiotic therapy. Other host factors that may determine whether disease develops include age, immunity, and presence or absence of intestinal receptors for the clostridial toxins. C difficile produces protein toxin A or B or both in the intestine. Toxin A is an enterotoxin that causes hypersecretion of fluid into the intestinal lumen and also causes tissue damage. Toxin B is a potent cytotoxin that induces inflammation and necrosis. Recent antibiotic therapy is a common feature of the history of horses with C difficile -induced diarrhea. Certain antibiotics, notably erythromycin, β-lactam antibiotics, and trimethoprim/sulfonamide, are more likely than others to be associated with C difficile colitis. Mares with foals that are being treated with erythromycin appear to be at high risk. Elimination of roughage from the diet prior to surgery is also reported to predispose to C difficile colitis.

C perfringens type A is believed to cause diarrhea by elaboration of an enterotoxin (CPE), which is released during sporulation and stimulates intestinal epithelial cells to secrete excess fluid into the lumen. A novel necrotizing toxin, called β2, produced by some strains of C perfringens , has recently been strongly associated with colitis in horses.

Clinical Findings:

Foals and adult horses may be affected. Typically there are signs of abdominal pain and diarrhea with or without blood. There may be abdominal distention, especially in cases of C difficile -induced diarrhea. Dehydration, toxemia, and shock may develop, and the mortality rate is variable. One or several animals on a farm may be affected.

Lesions:

The characteristic lesion is a necrotizing enterocolitis. There is severe loss of colonic and cecal mucosal epithelial cells, hemorrhagic colitis and typhlitis, and thrombosis in capillaries of the intestinal mucosa.

Diagnosis:

Clinical features of the disease are similar to those of acute salmonellosis ( Salmonellosis: Introduction), Potomac horse fever ( Potomac Horse Fever), or monocytic ehrlichiosis. The identification of C perfringens as the cause of diarrhea in horses depends on demonstration of the presence of enterotoxin or the gene for CPE in the feces or intestinal fluid and the absence of other likely etiologic agents. Most C perfringens found in the intestine of horses lack the gene for CPE. Demonstration of large numbers of bacterial spores or a high concentration of C perfringens in the feces are also aids to a diagnosis. The diagnosis of C difficile diarrhea is suggested by a history of recent treatment with antibiotics and is confirmed by demonstration of the presence of C difficile toxin A and/or B in a freshly passed or frozen fecal sample submitted to a laboratory. Toxin may be rapidly detected by an enzyme immunoassay, or the toxin gene may be identified by PCR.

Control:

Steps may be taken to reduce the opportunity for C difficile infections in horses. The use of antibiotics may be unavoidable in veterinary hospitals, but selection of antibiotics such as metronidazole and chloramphenicol for oral administration to high-risk horses is recommended. The sources of C difficile spores may be attacked by surface disinfection with a sporicidal disinfectant, and the spread may be reduced by hand washing and by isolation of infectious horses and foals. There are no control measures available for prevention of C perfringens -induced diarrhea. Oral metronidazole is recommended for treatment of either of these clostridial infections.