The comparative pathology of Clostridium difficile-associated disease.
Authors: Keel M K, Songer J G
Journal: Veterinary pathology
Summary
# Editorial Summary: *Clostridium difficile*-Associated Disease in Animals *Clostridium difficile* infection presents a complex pathological picture across mammalian species, with disease severity and location varying markedly depending on host factors including age, species susceptibility, antibiotic exposure, and environmental spore density. Keel and Songer's 2006 review synthesises comparative pathology findings, revealing that whilst most species develop disease predominantly in the caecum and colon, foals and rabbits notably develop severe jejunal involvement—a distinction that likely reflects differences in toxin-receptor distribution and colonisation rates between age groups and species. The pathogenic mechanism centres on two large exotoxins (TcdA and TcdB) that disrupt the actin cytoskeleton via Rho-signalling molecules after receptor-mediated endocytosis and endosomal acidification, causing cellular dysfunction compounded by inflammatory and neurogenic responses. For equine practitioners, this work underscores why antibiotic-associated colitis in horses represents a particularly serious manifestation of *C. difficile* disease, whilst the characterisation of differential toxin susceptibility helps explain why neonatal and young foals warrant especially cautious antimicrobial prescribing. Understanding these pathophysiological principles is essential for recognition of clinical presentations, informed antibiotic stewardship, and consideration of novel therapeutic approaches targeting toxin mechanisms rather than bacterial load alone.
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Practical Takeaways
- •Foals are uniquely susceptible to severe jejunal involvement with C. difficile; consider this diagnosis in antibiotic-treated foals with diarrhea involving the small intestine
- •Age and species dramatically influence disease presentation and severity—young horses show different lesion patterns than other species, requiring species-specific diagnostic and treatment approaches
- •Antibiotic administration remains a primary risk factor; minimize unnecessary antibiotic use in horses, particularly neonates, to reduce C. difficile-associated disease risk
Key Findings
- •C. difficile disease incidence varies greatly by host species, age, environmental spore density, and antibiotic exposure
- •Foals and rabbits develop severe jejunal lesions while most species are principally affected in cecum and colon
- •TcdA and TcdB toxins disrupt actin cytoskeleton via Rho-subtype intracellular signaling molecules, with TcdB receptors remaining uncharacterized
- •Disease is most commonly diagnosed in Syrian hamsters, horses, and neonatal pigs but occurs sporadically across many mammalian species