Scrapie in Sheep

Moredun-logoSummary written by Hugh Fraser BSc PhD

Taken from Moredun Foundation Newsheet Volume 2 No. 15 (1997)



  • ewe hayScrapie is an incurable disease affecting the brains of adult sheep.
  • Infection is passed to lambs from infected ewes, both pre- and post-natally.
  • Incubation periods range from two to over five years with a peak in three year old sheep.
  • Diagnosis can only be confirmed after death on brain histology although clinical diagnosis can be reliable.
  • The infectious agent is ill-defined and its identity unknown. Overwhelming evidence suggests than an altered host protein (PrP) is a major component.
  • Strain variation and mutation of scrapie agent imply genomic information which cannot be encoded in PrP.
  • The agent is highly resistant to all standard methods of microbiological decontamination.
  • Sheep PrP gene determines susceptibility to scrapie infection. There are breed differences in the details of PrP-gene determined susceptibility, perhaps depending on the dominating scrapie strain infecting the breed. A laboratory test is now available which should help in selection for resistance.
  • In infected flocks, almost all the highly susceptible genotype can develop scrapie. Importantly however, this genotype occurs in scrapie-free flocks and in countries such as Australia and New Zealand which are scrapie-free. This shows that scrapie is not a spontaneous genetic disease.
  • Control depends on culling affected sheep and their descendants. The selection for genetically ‘resistant’ sheep may confer benefit. However the need to maintain genetic diversity may be paramount and the continued presence of genetically susceptible healthy sheep validates scrapie-free status.



sheep cover2 smMore information on disease prevention can be found on the DVD 'Managing Your Flock for Peak Health' - programme 2 in the series 'Sheep on Your Smallholding'.







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