EGS Risk Factors

EGS affects horses, ponies and donkeys and occurs in all ages from 4 months to over 30 years.  There is however a strong peak of cases at 3-5 years old.  There is not thought to be any breed or sex predisposition.

Various risk factors have been identified through observational epidemiological studies including:

• Grazing
• The main risk, with only a couple of isolated reports of EGS in stabled horses
• Recent movement to new premises or pastures
  • Most cases are associated with exposure to new pasture within the preceding few weeks
• Age
  • All ages of horses are susceptible but most frequently cases are between 2-7 years old
• Previous occurrence of EGS on the premises
  • Premises that, particularly recently, have had a case of EGS provide increased risk
• Pasture disturbance
  • Several recent studies have identified increased risk by exposing horses to soil ingestion

Interestingly horses present on pastures when EGS occurred previously were found to have a reduced risk of the disease implying that exposure to the aetiological agent generates a protective immune response.

This picture shows the abdominal contents of an acute grass sickness case post-mortem.  The stomach has been cut open to reveal distension due to fluid accumulation.  This feature is responsible for the spontaneous naso-gastric reflux often seen in AGS and SAGS cases and can lead to the fatal complication of gastric rupture.  Small intestinal distension is also shown to the right of the picture due to the accumulation of liquid and gas.