RISK FACTORS FOR EGS
Observational epidemiological studies have identified several risk factors for EGS, and minimisation of these previously identified risk factors may help to reduce the likelihood of development of further cases.
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EGS is known to recur on previously affected premises, especially if cases occurred in the previous 2 years. EGS affects grazing horses, ponies and donkeys, usually young adults aged 2 – 7 years old, although cases have been reported in animals of all ages from 4 months to over 30 years. There is not thought to be any breed or sex predisposition; however one recent study reported that Scottish Native breeds may be more susceptible. Cases of EGS most frequently occur during spring and early summer months, with a notable peak incidence in May.
Various risk factors have been identified through epidemiological studies including:
- the main risk factor for EGS, 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
- all ages of horses are susceptible but those aged between 2 – 7 years old appear to be at greatest risk
- Previous occurrence of EGS on the premises
- premises that have had a previous case of EGS are at increased risk of further cases
- Pasture disturbance
- studies have identified increased risk where there is a history of pasture disturbance, presumably due to increasing the chance of soil ingestion
Interestingly horses grazing previously with EGS cases were found to have a reduced risk of the disease, implying that exposure to the aetiological agent could generate a protective immune response.