Clostridioides difficile is an important emerging pathogen that causes diarrhea primarily in neonatal swine. The agent was first recognized as a cause of antimicrobial-associated diarrhea in humans; however, antimicrobial-associated disease has not been reported in swine. Disease is most commonly observed in piglets 1–7 days old and is in response to C difficile toxins; thus, diagnostic approaches should focus on toxin detection.
Clostridioides difficile is an anaerobic, gram-positive, spore-forming rod that is more oxygen-sensitive than Clostridium perfringens. The organism can be demonstrated in the intestine by direct Gram stain of smears. Survival of C difficile in the environment and shedding by carrier sows is believed to be important in transmission. C difficile proliferates in the cecum and spiral colon of pigs, where it produces two major toxins (A and B) that are involved in lesion production. Toxin A is an enterotoxin that causes fluid secretion into the gut lumen; toxin B is a cytotoxin and enterotoxin.
Piglets infected by C difficile often have diarrhea from birth, and disease is observed in approximately one-third of affected litters. Occasionally, individual pigs have dyspnea, abdominal distention, and scrotal edema.
The most common postmortem lesion of C difficile enteritis is moderate to severe mesocolonic edema, with yellowish, pasty to watery contents. Ascites and hydrothorax may be observed with severe systemic disease. Microscopically, the colon is primarily affected, with multifocal exudation of neutrophils and fibrin into the lumen and expansion of the submucosa and mesentery by edematous fluid and few leukocytes.
Gross lesions are not pathognomonic, and diagnosis must be confirmed by a combination of culture, demonstration of either toxin A or B, and histopathologic evaluation. C difficile can be cultured on selective media containing cefoxitin, cycloserine, taurocholate, and fructose under anaerobic conditions. The genes of toxins A and B are identified readily by PCR assay. The toxins can also be detected directly in suspensions of intestinal contents by commercially available enzyme immunoassays.
Minimum inhibitory concentration determinations suggest that erythromycin, tetracycline, and tylosin may be useful for treatment of C difficile enteritis in suckling piglets, and tiamulin and virginiamycin may help to reduce levels of the organism in adult swine. No controlled studies on the effect of antimicrobials on clinical signs of disease have been reported. Although immunoprophylaxis for C difficile infections in pigs has not been extensively studied, results in rodent models suggest that antitoxic approaches may be of value.