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

This study investigates the risk factors that contribute to equine grass sickness (EGS), or dysautonomia, recurring on premises that have previously recorded cases. The survey utilized a postal questionnaire sent to premises that had EGS cases from 1997-2001 to understand the disease’s pattern of recurrence. The researchers discovered that premises with more horses, younger animals, specific soil types (loam and sand), and those who mechanically remove droppings had higher recurrence rates. Conversely, pastures with chalk soil, cograzing ruminants, and where droppings were hand-removed showed reduced recurrence. The findings suggest that EGS may be a toxico-infectious form of botulism, influenced significantly by soil conditions and livestock management practices.

Objective of the Study

• The main purpose of this research is to identify the risk factors that contribute to the recurring cases of EGS on premises where it has been previously reported.
• Furthermore, the study seeks to provide valuable insights into the pathogenesis – the biological mechanism that leads to the disease – of EGS.

Methods Used in the Study

• Data on the disease history and risk factors was collected through a postal questionnaire.
• The questionnaire was delivered to premises with reported EGS cases between the 1st of January 1997 and 31st December 2001.
• The research team analysed the collected information using Poisson regression analysis, a statistical technique for determining the variation in the recurrence of EGS concerning different risk factors.

Results and Findings

• From a total of 509 premises that were included in the survey, 305 returned fill-up forms, out of which 100 were classified as ‘recurrent’ premises.
• An overall median incidence rate for EGS of 2.1 EGS incidents per 100 horses per premises per year was recorded.
• The investigation found increased recurrence rates in premises with a higher number of horses, the presence of younger animals, stud farms and livery/riding establishments, loam and sand soils, rearing of domestic birds and mechanical droppings removal.
• Conversely, a decrease in EGS recurrence rate was linked with chalk soil, the practice of cograzing ruminants, grass cutting on pastures and hand removal of droppings.

Conclusions

• The findings from the study suggest that EGS is likely a toxico-infectious form of botulism.
• The significant risk factors identified predominantly relate to soil disturbance and the consequent contamination of grass, increasing the exposure of grazing horses to Clostridium botulinum, a bacterium found in soil that could be the causative agent of EGS.
• The researchers state that potentially modifiable risk factors that have been identified in this study could lead to practical measures to mitigate EGS’s incidence rate on premises where it has previously occurred.