Equine grass sickness, but not botulism, causes autonomic and enteric neurodegeneration and increases soluble N-ethylmaleimide-sensitive factor attachment receptor protein expression within neuronal perikarya.
Authors: McGorum B C, Scholes S, Milne E M, Eaton S L, Wishart T M, Poxton I R, Moss S, Wernery U, Davey T, Harris J B, Pirie R S
Journal: Equine veterinary journal
Summary
# Editorial Summary Equine grass sickness (EGS) remains a significant clinical challenge with poorly understood underlying mechanisms, though some evidence points to *Clostridium botulinum* toxins as a potential aetiological agent. McGorum and colleagues investigated whether EGS causes the same neurological damage as botulism by examining SNARE protein expression (the functional targets of botulinum neurotoxins) and assessing neurodegeneration in autonomic and enteric nervous system tissues from affected horses, experimentally botulism-affected horses, and unaffected controls. The key finding was that EGS causes significant autonomic and enteric neuronal degeneration alongside elevated soluble SNARE protein expression within nerve cell bodies—a pattern distinctly absent in botulism-affected horses despite similar clinical presentations in some cases. This differential neuronal damage profile suggests that whilst botulism and EGS may share some clinical features, EGS involves a distinct pathological mechanism affecting the nervous system beyond simple neurotoxin-mediated SNARE protein cleavage. For practitioners managing EGS cases, these findings reinforce that the condition involves primary neurodegeneration rather than reversible neuromuscular blockade, which has implications for prognosis and the limited role of symptomatic treatment alone.
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Practical Takeaways
- •EGS and equine botulism are distinct diseases with different pathological mechanisms—EGS causes neuronal death in autonomic and gut systems while botulism does not, which may inform diagnostic and treatment strategies
- •The presence of neurodegeneration in EGS suggests a direct toxic or infectious effect on nerve cells rather than simple neurotransmitter blockade, potentially opening new therapeutic avenues beyond current supportive care
- •Even if C. botulinum is involved in EGS aetiology, the disease pathology differs fundamentally from classic botulism, warranting distinct clinical management approaches
Key Findings
- •EGS causes autonomic and enteric neurodegeneration with increased SNARE protein expression in neuronal perikarya, distinguishing it pathologically from botulism
- •Equine botulism does not cause autonomic and enteric neurodegeneration despite potential C. botulinum involvement in EGS aetiology
- •SNARE protein accumulation in EGS represents a distinct pathological mechanism differentiating it from botulinum neurotoxin effects