Two cases of equine grass sickness with evidence for soil-borne origin involving botulinum neurotoxin.

This study suggests that a disease affecting horses known as equine grass sickness is a form of botulism caused by a particular type of bacteria found in the soil, Clostridium botulinum. Evidence from the research highlighted instances of this toxin being present in botulinum-contaminated grass and soil samples as well as in necropsy specimens from sick horses.

About the Disease and Its Cause

• Botulism is a serious illness caused by the bacterium Clostridium botulinum. The bacteria are commonly found in soil and can produce a powerful neurotoxin.
• The neurotoxin produced can cause weakness or paralysis. In horses, a disease known as equine grass sickness (also known as equine dysautonomia) exhibits these symptoms and researchers suspect it’s a clinical manifestation of botulism.

Details of the Study

• The study was conducted on a stud where equine grass sickness had occurred twice within an 8-month period.
• Researchers examined grass and soil samples from the affected area, as well as necropsy specimens from one of the sick horses. These were tested for the presence of Clostridium botulinum and its neurotoxin.
• Different types and mixtures (A-E) of Clostridium botulinum and botulinum neurotoxin were identified in the samples.

Key Findings

• For the first time, researchers found that green grass blades can contain botulinum toxin. This was a significant finding as it demonstrated a clear linkage between the environment in which the horses grazed and their health outcomes.
• The findings lend support to the hypothesis that equine grass sickness is essentially a manifestation of botulism, a disease that has a soil-borne origin.