Systemic antibodies to Clostridium botulinum type C: do they protect horses from grass sickness (dysautonomia)?
Authors: Hunter L C, Poxton I R
Journal: Equine veterinary journal
Summary
# Editorial Summary: Systemic Antibodies and Grass Sickness Susceptibility Equine grass sickness (dysautonomia) remains poorly understood, though evidence increasingly implicates *Clostridium botulinum* type C toxicoinfection; Hunter and Poxton investigated whether protective immunity to this bacterium and its neurotoxin correlates with resistance to the disease. By measuring systemic IgG antibodies against *C. botulinum* type C surface antigens and botulinum neurotoxin type C (BoNT/C) in affected and unaffected horses, the researchers found that grass sickness cases had significantly lower antibody levels to both targets compared with healthy controls, suggesting impaired systemic immunity may increase susceptibility. Notably, horses with prior exposure to affected pastures or contact with clinical cases showed substantially elevated antibody titres, indicating subclinical exposure generates protective responses; however, antibody levels did not correlate with disease severity categories, suggesting systemic immunity influences whether infection occurs rather than its progression. These findings have considerable implications for prevention strategies: if *C. botulinum* type C is indeed the aetiological agent, vaccination could theoretically confer protection by stimulating the antibody responses that naturally exposed horses develop. Practitioners should consider this research when counselling on risk factors for grass sickness and may anticipate future vaccine development, though further investigation into mucosal and cellular immunity—alongside confirmation of the bacterium's role—remains essential before clinical application.
Read the full abstract on PubMed
Practical Takeaways
- •Horses with prior exposure to grass sickness or affected pastures may have developed natural immunity; consider this when assessing disease risk on individual properties
- •Vaccination against C. botulinum type C could potentially prevent EGS by stimulating protective antibody responses, though further development is needed
- •Younger horses and those newly introduced to pastures with EGS history may be at higher risk due to lack of prior exposure and antibody development
Key Findings
- •Horses with grass sickness had significantly lower systemic IgG antibody levels to C. botulinum type C surface antigens and botulinum neurotoxin (BoNT/C) compared to healthy horses
- •Horses with prior EGS contact or grazing on pastures with frequent EGS history showed significantly higher antibody levels, suggesting protective immune response from subclinical exposure
- •Systemic immunity to C. botulinum type C does not influence disease severity, as no significant differences in antibody levels were found between different EGS categories
- •Low levels of systemic immunity to C. botulinum type C antigens may increase susceptibility to developing equine grass sickness