Equine grass sickness is associated with low antibody levels to Clostridium botulinum: a matched case-control study.
Abstract: Equine grass sickness is a high mortality disease which, despite many years of investigation, is of unknown aetiology. Recent findings indicating that the disease is associated with Clostridium botulinum require support from an epidemiological study that recognises and controls for potential confounders, e.g. age, time of year and premises. Objective: EGS is associated with low antibody levels to C. botulinum antigens. Methods: A matched case-control study was conducted. Data were collected from 66 histologically confirmed cases of EGS and 132 premises-matched control horses. The probability of EGS in horses was modelled using conditional logistic regression. Results: EGS was significantly associated (age-adjusted P < 0.005) with low antibody levels to each of 3 clostridial antigens; C. botulinum type C and C. novyi type A surface antigens and a C. botulinum type C toxin complex toxoid. These serological risk factors for EGS remained highly significant when entered into multivariable models. This study also identified new horse-level risk factors for EGS; feeding hay or haylage was associated with a decreased risk of disease, change of feed type or quantity during the 14 days prior to disease was associated with increased risk, and the use of an ivermectin anthelmintic at both the ultimate and penultimate treatments was also associated with a significantly increased risk of EGS. Conclusions: This study provides strong support for the role of C. botulinum in the aetiology of EGS and identifies managemental risk factors for the disease. Conclusions: Increasing anticlostridial antibody levels by vaccination and appropriate managemental interventions may decrease the risk of EGS occurring.
Publication Date: 2004-03-25 PubMed ID: 15038434
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- Journal Article
- Research Support
- Non-U.S. Gov't
Summary
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The research discovered a strong correlation between Equine grass sickness (EGS), a fatal disease among horses, and low antibody levels to Clostridium botulinum. The study suggests possible preventive measures like vaccination and controlling other risk factors such as modifying horse-feeding habits.
Objective and Methods of Study
The objective of this study was to explore whether Equine grass sickness (EGS), a disease with high mortality rate among horses and unknown cause, was linked to low antibody levels to Clostridium botulinum antigens.
- A case-control study design was used for this research.
- 66 histologically confirmed EGS cases were used alongside 132 control horses that were matched according to the premises.
- Modelling of the probability of EGS in horses was done using conditional logistic regression.
Findings of the Study
Multiple findings were discovered through this research:
- EGS was found to be significantly associated with low antibody levels for three clostridial antigens; C. botulinum type C, C. novyi type A, and a C. botulinum type C toxin complex toxoid.
- These serological risk factors remained significant even when other variables were considered.
- The study also found new horse-level risk factors associated with EGS: changing the feed type or quantity during the 14 days prior to the disease was associated with an increased risk, and the use of an ivermectin anthelmintic at both the ultimate and penultimate treatments significantly increased the risk of EGS.
- In contrast, feeding hay or haylage to horses was associated with decreased risk of the disease.
Conclusions of the Study
This research provides compelling evidence for the role of Clostridium botulinum in the development of EGS and identifies management risk factors for the disease.
- A major conclusion from this study is that increasing anticlostridial antibody levels through vaccination and incorporating appropriate management interventions could potentially reduce the risk of EGS in horses.
- The study also highlights the need to control other identified risk factors, such as feed changes and use of certain treatments, to further mitigate the risks.
Cite This Article
APA
McCarthy HE, French NP, Edwards GB, Poxton IR, Kelly DF, Payne-Johnson CE, Miller K, Proudman CJ.
(2004).
Equine grass sickness is associated with low antibody levels to Clostridium botulinum: a matched case-control study.
Equine Vet J, 36(2), 123-129.
Publication
Researcher Affiliations
- Faculty of Veterinary Science, University of Liverpool, Leahurst, Neston, Wirral CH64 7TE, UK.
MeSH Terms
- Animals
- Antibodies, Bacterial / blood
- Antigens, Bacterial / immunology
- Antigens, Surface / immunology
- Autonomic Nervous System Diseases / blood
- Autonomic Nervous System Diseases / etiology
- Autonomic Nervous System Diseases / microbiology
- Autonomic Nervous System Diseases / veterinary
- Botulinum Toxins / immunology
- Case-Control Studies
- Clostridium botulinum / immunology
- Female
- Horse Diseases / blood
- Horse Diseases / etiology
- Horse Diseases / microbiology
- Horses
- Logistic Models
- Male
- Poaceae / microbiology
- Risk Factors
- Vaccination / veterinary
Citations
This article has been cited 6 times.- McGorum BC, Chen Z, Glendinning L, Gweon HS, Hunt L, Ivens A, Keen JA, Pirie RS, Taylor J, Wilkinson T, McLachlan G. Equine grass sickness (a multiple systems neuropathy) is associated with alterations in the gastrointestinal mycobiome. Anim Microbiome 2021 Oct 9;3(1):70.
- McGorum BC, Symonds HW, Knottenbelt C, Cave TA, MacDonald SJ, Stratton J, Leon I, Turner JA, Pirie RS. Alterations in amino acid status in cats with feline dysautonomia. PLoS One 2017;12(3):e0174346.
- Archer DC, Pinchbeck GL, Proudman CJ, Clough HE. Is equine colic seasonal? Novel application of a model based approach. BMC Vet Res 2006 Aug 24;2:27.
- Atkins CN, Hahn CN, McGorum BC. Comparison of Dysautonomia Across Species: Current Knowledge and Future Research Opportunities. J Vet Intern Med 2025 Jul-Aug;39(4):e70140.
- Slavik K, Whitlock R, Johnson A. Equine botulism. Equine Vet J 2026 Mar;58(2):333-347.
- McGorum BC, Davey T, Dosi MCM, Keen JA, Morrison LR, Pirie RS, Shaw DJ, Harris JB. Equine grass sickness is associated with major abnormalities in the ultrastructure of skeletal neuromuscular junctions. Equine Vet J 2025 Jan;57(1):193-202.
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