An epidemiological study of risk factors associated with the recurrence of equine grass sickness (dysautonomia) on previously affected premises

Abstract

Summary Reasons for performing study: The reasons why equine grass sickness (EGS) recurs on premises are unknown and, consequently, practical methods for reducing the risk of recurrence are not available. Objectives: To identify risk factors associated with recurrence of EGS on premises and to gain possible insights into the pathogenesis of the disease. Methods: Data on disease history and risk factors were collected by postal questionnaire from premises with EGS cases between 1st January 1997 and 31st December 2001. Data on variation in rates of recurrence of EGS for different risk factors were analysed using Poisson regression analysis. Results: Of 509 premises contacted, 305 (60%) returned useable questionnaires and 100 of these (33%) were classified as ‘recurrent’ premises. An overall median incidence rate for EGS of 2.1 EGS incidents/100 horses/premises/year was recorded. There was an increased rate of recurrence with higher numbers of horses, presence of younger animals, stud farms and livery/riding establishments, loam and sand soils, rearing of domestic birds and mechanical droppings removal. The rate of recurrence decreased with chalk soil, cograzing ruminants, grass cutting on pastures and removal of droppings by hand. Several statistically significant interactions were identified. Conclusions: Many of the findings are consistent with the theory that EGS is a toxico‐infectious form of botulism. Several of the significant factors identified may directly or indirectly relate to soil disturbance and consequent soil contamination of grass, thereby increasing the rate of exposure of grazing horses to Clostridium botulinum, which resides in soil. Potential relevance: Identification of potentially modifiable risk factors may, ideally following validation in appropriately designed, controlled and randomised intervention studies, lead to practical measures to reduce the incidence of EGS on previously affected premises.

Neurodegenerative Disorders

“…75 Another study compared premises with recurrent EGS with those that had a single, unprecedented EGS incident. 76 This comparison revealed that high horse numbers, predominance of young horses, sandy or loamy soils, and mechanical removal of feces were premise-level risk factors. Chalky soil, manual removal of feces from pastures, pasture grass mowing, and co-grazing with ruminants were protective factors associated with lower recurrence rates for EGS.…”

“…In light of the putative causal association between C. botulinum type C and EGS, there is great interest 19 / Neurodegenerative Disorders 249 in the development of vaccines; 76 testing of candidate products should begin within the next several years. Current efforts at prevention involve minimization of known risk factors and introduction of suspected protective practices.…”

Differential Diagnosis and Management of Cranial Nerve Abnormalities

“…[42][43][44][45][46] Grass sickness is reported in the United Kingdom, Europe, and is also reported in several countries in South America. Clinical signs of grass sickness are characterized as acute, subacute, or chronic according to the duration and severity of clinical signs.…”

“…Grass sickness is consistently associated with grazing grass. 42 There is evidence that toxicoinfection with Clostridium botulinum type C may be involved with the pathogenesis of grass sickness. 43-46 Hunter et al (2001) 45 demonstrated the presence of one of the toxins produced by C. botulinum type C in 44% of horses with grass sickness compared to 4% in control horses.…”

Edaphic and Phytochemical Factors as Predictors of Equine Grass Sickness Cases in the UK

“…Epidemiological evidence from the United Kingdom indicates that EGS is a non-contagious disease (Gilmour and Jolly, 1974), but linked to certain sites (Wood et al, 1998; McCarthy et al, 2004; Newton et al, 2004). It is seasonal (with most cases occurring between April and July); and likely to be caused by an unknown constituent in the horses’ diet and/or environment (Wood et al, 1998; Newton et al, 2004; French et al, 2005).…”