BSE: Science & research - Research to support the National Scrapie Plan and control strategies
The National Scrapie Plan (NSP) for GB was launched in 2001 following recommendations from the sheep subgroup 
of the Spongiform Encephalopathy Advisory Committee in 1999. The NSP is a strategic long-term plan which consists of a breeding programme to increase the number of sheep within the nation flock that are naturally resistant to scrapie. The objective of the NSP is to reduce and eventually eradicate TSEs like scrapie as this would be beneficial in terms of its effect on animal health and on the reduction of the theoretical risk arising from the possible presence of BSE in sheep.
Genetic resistance to scrapie
Early research into scrapie has shown the prion protein gene (called the PRNP gene) in sheep has a role in conferring susceptibility or resistance to the development of scrapie. In particular the amino acids at position 136, 154 and 171 of the prion protein are strongly associated with the susceptibility of the sheep to become infected with scrapie. In addition, allele 141 is associated with susceptibility to atypical scrapie.
Further information is available on NSP genotyping including an explanation of the terminology. In summary, the ARR allele of the PRNP gene is associated with low disease risk and the ARQ and VRQ alleles are associated with a moderate to high disease risk.
Recently funded research
Since the introduction of the NSP in 2001, Defra has continued to fund further work to address areas of uncertainty. This work includes studies to investigate the recommendations for future research made by the SEAC subgroup in 1999 and covers:
- Further work on PRNP genotypes;
- Scrapie in goats;
- Investigation of whether a carrier state can exist;
- Transmission routes of scrapie: How does scrapie spread from sheep to sheep?
- Epidemiology and modelling studies for control strategies.
Further work on PRNP genotypes
A number of research projects have been funded to refine our knowledge on the genotypes affected by scrapie and experimental BSE. These projects include:
Further information on the effect of PRNP gene polymorphisms (variations) on susceptibility to TSE infection.
Research was funded to confirm that sheep of various PrP genotypes from New Zealand, which is free of classical scrapie, respond to experimental infection with TSEs in the same manner as sheep from the UK (project SE1432).
In addition the study also provided useful information on the association of TSE susceptibility / resistance to PrP genotype. It was discovered in this project that ARR/ARR sheep are susceptible to intracerebral challenge with BSE (project SE1432).
Following the observation in ARR/ARR, a complementary study has been set up to investigate the susceptibility of these sheep to intracerebral challenge of classical scrapie (project SE1851).
Effect of PRNP gene polymorphisms (variations) on susceptibility to infection with atypical scrapie
Research has been undertaken to investigate whether PrP genotypes influence susceptibility of sheep to atypical scrapie in the UK (project SE0240). See atypical scrapie research.
Scrapie in goats
Effect of PrP gene polymorphisms (variations) on susceptibility of goats to TSEs
Research is underway to establish whether PrP gene polymorphisms influence the susceptibility of goats to scrapie and BSE (project SE1442).
Investigation of whether a carrier state can exist
There is a concern that relatively resistant sheep, e.g. sheep with the homozygous ARR/ARR genotype, could act as carriers of TSEs without showing any clinical signs of disease (otherwise known as a carrier state). It is important to explore this possibility as it could have implications on the control of TSEs in sheep. Three projects are currently ongoing to investigate this: SE1852, SE1853 & SE1854.
Transmission routes of scrapie: How does scrapie spread from sheep to sheep?
Scrapie is known to be an infectious disease that can be transmitted between individuals. Research is ongoing to determine the natural routes of transmission of scrapie infection within flocks. This includes investigating the transmission of disease between sheep (horizontal transmission) and transmission of disease from parents to lambs (vertical transmission).
- Horizontal transmission - Research is still in progress but the results so far have shown that classical scrapie can be transmitted during the perinatal period and throughout the life of the animal. Exposure to contaminated pasture alone, without any direct animal to animal contact, appears sufficient to initiate an infection (project SE1845).
- See further information on TSE persistence in the environment;
- Maternal transmission - There is evidence that classical scrapie is transmitted from an infected ewe to her lamb around the time of birth. Pregnancy-related tissues and fluids are being analysed for the presence of disease-associated prion protein to investigate the potential sources of scrapie infection during the prenatal and perinatal period. In addition, three projects are examining milk and colostrum as a possible route of transmission (projects SE1834, SE1843, SE1855, SE1856, SE1857 & SE2004).
Epidemiology and modelling studies for control strategies
Both the genetics of the susceptibility of TSEs and the structure of the national flock are complicated. Therefore, any control strategy for TSEs in sheep requires the support of well-characterised models that can be used to predict the effect of different actions in various circumstances.
These include modelling studies to:
- Investigate the transmission of scrapie both between and within flocks (project SE0228).
- Assess the impact of possible changes to the NSP (project SE0238).
- Determine the best sampling strategy to determine the PrP genotype profile of the slaughter lamb population in GB (project SE0244).
- Determine the effect of the NSP on sheep traits of economic importance. Also, to advise on optimal selection methods for scrapie resistance in terms of an overall genetic improvement programme (project SE0236).
- Evaluate the specific effects of selecting for genetic resistance to scrapie on UK rare sheep breeds (project SE0235).
- Provide estimates of the prevalence of scrapie infection in GB sheep and to advise on any modifications to the existing surveillance activities (project SE0243).
Action taken
- Data from the studies above and the Defra-funded work investigating BSE in sheep and atypical scrapie has been fed into numerous risk assessments and used to ensure that current TSE controls are proportionate and based on the latest scientific knowledge.
- A review of the NSP Ram Genotyping Scheme was carried out in late 2006 following a decision by the EU Council and European Parliament not to implement proposals for compulsory breeding of scrapie resistance in pure breed and pedigree flocks. The review included an examination by the Spongiform Encephalopathy Advisory Committee (SEAC) of the research underpinning the NSP, much of which was funded by Defra.
Links to further information
Page last modified: 18 March, 2008