Etiology: Clostridium spiroforme, Clostridium difficile and Clostridium perfringens are Gram-positive, spore-forming anaerobic bacilli. C. spiriforme produces exotoxin which is biologically and antigenically similar to C. perfringens type E iota toxin. Clostridium difficile produces two toxins. Toxin A is an enterotoxin that binds to enterocyte receptors, causing fluid secretion and enterocyte damage associated with disease. Toxin B is a cytotoxin that causes cell death in vitro, but exact effects in vivo are unknown.
C. spiroforme, C. difficile and C. perfringens are not considered normal flora in healthy rabbits.
Incidence: The incidence of infection is moderate to low.
Transmission: C. spiroforme, C. difficile and C. perfringens are transmitted by the fecal-oral route, and overgrowth is precipitated by factors that disrupt gut flora.
Clinical Signs: Death may be seen without observation of clinical disease. Anorexia may be seen several hours before the onset of diarrhea. Diarrhea is watery brown; rabbits are often moribund, dehydrated, and hypothermic; death usually occurs 1 to 2 days after onset of diarrhea.
Pathology: Gross lesions include fluid cecal contents with serosal hemorrhages and edema on the cecum, and occasionally the ileum and proximal colon (A). Microscopically, there is necrotic erosive or ulcerative typhlitis with swollen or vacuolated enterocytes, pseudomembrane formation, heterophilic infiltration, as well as submucosal edema and hemorrhage (B). Large Gram-positive bacilli are present on the mucosal surface.
Diagnosis: Diagnosis of Clostridial species can be made by performing a Gram stain on impression smears and collecting feces for toxin analysis, culture, and PCR. Gross and microscopic lesions are characteristic but not diagnostic.