Scrapie control in Great Britain (GB) was originally based on the National Scrapie Plan's Ram Genotyping scheme aimed at reducing the susceptibility of the national flock. The current official strategy to control scrapie in the national flock involves culling susceptible genotypes in individual, known affected flocks (compulsory scrapie flock scheme or CSFS). However, the recent development of preclinical test candidates means that a strategy based on disease detection may now be feasible. Here, a deterministic within-flock model was used to demonstrate that only large flocks with many home-bred ewes are likely to be a significant risk for flock-to-flock transmission of scrapie. For most other flocks, it was found that the CSFS could be replaced by a strategy using a currently available live test without excessive risk to other farmers, even if the proportion of susceptible genotypes in the flock is unusually large. Even for flocks that represent a high risk of harbouring a high prevalence of infection, there would be limited probability of onward transmission if scrapie is detected soon after disease introduction (typically less than 5 years). However, if detection of disease is delayed, the existing CSFS strategy may be the most appropriate control measure in these cases.
Baylis, M., Houston, F., Kao, R. R., McLean, A., Hunter, N. & Gravenor, M. B.(2002). BSE – a wolf in sheep's clothing? Trends Microbiol10, 563–570.[CrossRef][Google Scholar]
Bruce, M. E., Will, R. G., Ironside, J. W., McConnell, I., Drummond, D., Suttie, A., McCardle, L., Chree, A., Hope, J. & other authors(1997). Transmissions to mice indicate that ‘new variant’ CJD is caused by the BSE agent. Nature389, 498–501.[CrossRef][Google Scholar]
Caughey, B. & Chesebro, B.(1997). Prion protein and the transmissible spongiform encephalopathies. Trends Cell Biol7, 56–62.[CrossRef][Google Scholar]
Dohoo, I., Martin, W. & Stryhn, H.(2003). Screening and diagnostic tests. In Veterinary Epidemiologic Research, pp. 86–115. Charlottetown, Prince Edward Island. : AVC.
[Google Scholar]
Foster, J. D., Hope, J. & Fraser, H.(1993). Transmission of bovine spongiform encephalopathy to sheep and goats. Vet Rec133, 339–341.[CrossRef][Google Scholar]
Fryer, H. R., Baylis, M., Sivam, K. & McLean, A.(2007). Quantifying the risk from ovine BSE and the impact of control strategies. Proc Biol Sci274, 1497–1503.[CrossRef][Google Scholar]
Goldmann, W., Hunter, N., Smith, G., Foster, J. & Hope, J.(1994). PrP genotype and agent effects in scrapie: change in allelic interaction with different isolates of agent in sheep, a natural host of scrapie. J Gen Virol75, 989–995.[CrossRef][Google Scholar]
González, L., Dalgleish, M. P., Martin, S., Dexter, G., Steele, P., Finalyson, J. & Jeffrey, M.(2008a). Diagnosis of preclinical scrapie in live sheep by the immunohistochemical examination of rectal biopsies. Vet Rec162, 397–403.[CrossRef][Google Scholar]
González, L., Horton, R., Ramsay, D., Toomik, R., Leathers, V., Tonelli, Q., Dagleish, M. P., Jeffrey, M. & Terry, L.(2008b). Adaptation and evaluation of a rapid test for the diagnosis of sheep scrapie in samples of rectal mucosa. J Vet Diagn Invest20, 203–208.[CrossRef][Google Scholar]
Gravenor, M. B., Cox, D. R., Hoinville, L. J., Hoek, A. & Mclean, A. R.(2001). The flock-to-flock force of infection for scrapie in Britain. Proc Biol Sci268, 587–592.[CrossRef][Google Scholar]
Green, D. M., del Rio Vilas, V. J., Birch, C. P. D., Johnson, J., Kiss, I. Z., McCarthy, N. D. & Kao, R. R.(2007). Demographic risk factors for classical and atypical scrapie in Great Britain. J Gen Virol88, 3486–3492.[CrossRef][Google Scholar]
Gubbins, S.(2005). A modelling framework to describe the spread of scrapie between sheep flocks in Great Britain. Prev Vet Med67, 143–156.[CrossRef][Google Scholar]
Gubbins, S. & Webb, C. R.(2005). Simulation of the options for a national control programme to eradicate scrapie from Great Britain. Prev Vet Med69, 175–187.[CrossRef][Google Scholar]
Hagenaars, T. J., Donnelly, C. A., Ferguson, N. M. & Anderson, R. M.(2000). The transmission dynamics of the aetiological agent of scrapie in a sheep flock. Math Biosci168, 117–135.[CrossRef][Google Scholar]
Healy, A. M., Hannon, D., Morgan, K. L., Weavers, E., Collins, J. D. & Doherty, M. L.(2004). A paired case-control study of risk factors for scrapie in Irish sheep flocks. Prev Vet Med64, 73–83.[CrossRef][Google Scholar]
Hill, A. F., Desbruslais, M., Joiner, S., Sidle, K. C. L., Gowland, I., Collinge, J., Doey, L. J. & Lantos, P.(1997a). The same prion strain causes vCJD and BSE. Nature389, 448–450.[CrossRef][Google Scholar]
Hill, A. F., Zeidler, M., Ironside, J. & Collinge, J.(1997b). Diagnosis of a new variant Creutzfeld–Jakob disease by tonsil biopsy. Lancet349, 99–100.[CrossRef][Google Scholar]
Hopp, P., Ulvund, M. J. & Jarp, J.(2001). A case-control study on scrapie in Norwegian sheep flocks. Prev Vet Med51, 183–198.[CrossRef][Google Scholar]
Houston, E. F. & Gravenor, M. B.(2003). Clinical signs in sheep experimentally infected with scrapie and BSE. Vet Rec152, 333.[CrossRef][Google Scholar]
Jeffrey, M., Ryder, S., Martin, S., Hawkins, S. A., Terry, L., Berthelin-Baker, C. & Bellworthy, S. J.(2001). Oral inoculation of sheep with the agent of bovine spongiform encephalopathy (BSE). 1. Onset and distribution of disease-specific PrP accumulation in brain and viscera. J Comp Pathol124, 280–289.[CrossRef][Google Scholar]
Kao, R. R., Gravenor, M. B. & McLean, A. R.(2001). Modelling the national scrapie eradication programme in the UK. Math Biosci174, 61–76.[CrossRef][Google Scholar]
Kao, R. R., Gravenor, M. B., Baylis, M., Bostock, C. J., Chihota, C. M., Evans, J. C., Goldmann, W., Smith, A. J. & McLean, A.(2002). The potential size and duration of an epidemic of bovine spongiform encephalopathy in British sheep. Science295, 332–335.[CrossRef][Google Scholar]
Kao, R. R., Green, D. M., Johnson, J. & Kiss, I. Z.(2007). Disease dynamics over very different timescales: FMD and scrapie on the network of livestock movements in the UK. J R Soc Interface4, 907–916.[CrossRef][Google Scholar]
Konold, T., Moore, S. J., Bellworthy, S. J. & Simmons, H. A.(2008). Evidence of scrapie transmission via milk. BMC Vet Res4, 14.[CrossRef][Google Scholar]
McLean, A. R., Hoek, A., Hoinville, L. J. & Gravenor, M. B.(1999). Scrapie transmission in Britain: a recipe for a mathematical model. Proc Biol Sci266, 2531–2538.[CrossRef][Google Scholar]
O'Rourke, K. I., Baszler, T. V., Besser, T. E., Miller, J. M., Cutlip, R. C., Wells, G. A., Ryder, S. J., Parish, S. M., Hamir, A. N. & other authors(2000). Preclinical diagnosis of scrapie by immunohistochemistry of third eyelid lymphoid tissue. J Clin Microbiol38, 3254–3259.
[Google Scholar]
Ortiz-Pelaez, A. & Del Rio Vilas, V. J.(2009). Within-holding prevalence of sheep classical scrapie in Great Britain. BMC Vet Res5, 1.[CrossRef][Google Scholar]
Parry, H. B.(2003).Scrapie Disease in Sheep: Historical, Clinical, Epidemiological, Pathological and Practical Aspects of the Natural Disease, p. 146. Edited by Oppenheimer, D. R.. London. : Academic Press.
[Google Scholar]
Race, R., Jenny, A. & Sutton, D.(1998). Scrapie infectivity and proteinase K-resistant prion protein in sheep placenta, brain, spleen, and lymph node: implications for transmission and antemortem diagnosis. J Infect Dis178, 949–953.[CrossRef][Google Scholar]
Radostitis, O. M., Gay, C. C., Blood, D. C. & Hinchcliff, K. W.(2000). Diseases caused by viruses and Chlamydia-II. In Veterinary Medicine: a Textbook of the Disease of Cattle, Sheep, Pigs, Goats and Horses, 9th edn, pp. 115–1260. Edited by Radostitis, O., Gay, C. C., Blood, D. C. & Hinchcliff, K. W.. London. : W. B. Saunders.
[Google Scholar]
Schreuder, B. E., van Keulen, L. J., Vromans, M. E., Langeveld, J. P. & Smits, M. A.(1998). Tonsillar biopsy and PrPSc detection in the preclinical diagnosis of scrapie. Vet Rec142, 564–568.[CrossRef][Google Scholar]
Sivam, S. K., Baylis, M., Gravenor, M. B. & Gubbins, S.(2006). Descriptive analysis of an anonymous postal survey of the occurrence of scrapie in Great Britain in 2002. Vet Rec158, 501–506.[CrossRef][Google Scholar]
Somerville, R. A., Birkett, C. R., Farquhar, C. F., Hunter, N., Goldmann, W., Dornan, J., Grover, D., Hennion, R. M., Percy, C. & other authors(1997). Immunodetection of PrPSc in spleens of some scrapie-infected sheep but not BSE-infected cows. J Gen Virol78, 2389–2396.
[Google Scholar]
Stringer, S. M., Hunter, N. & Woolhouse, M. E. J.(1998). A mathematical model of the dynamics of scrapie in a sheep flock. Math Biosci153, 79–98.[CrossRef][Google Scholar]
Truscott, J. E. & Ferguson, N. M.(2009). Control of scrapie in the UK sheep population. Epidemiol Infect137, 775–786.[CrossRef][Google Scholar]
VLA(2003a). Summary of the results of the scrapie surveillance in sheep in Great Britain. January 2002–March 2003: Veterinary Laboratories Agency.
VLA(2003b). Summary of the results of the scrapie surveillance in sheep in Great Britain. April–December 2003: Veterinary Laboratories Agency.
Webb, C. R.(2005). Farm animal networks: unravelling the contact structure of the British sheep population. Prev Vet Med68, 3–17.[CrossRef][Google Scholar]
Woolhouse, M. E. J., Stringer, S. M., Matthews, L., Hunter, N. & Anderson, R. M.(1998). Epidemiology and control of scrapie within a sheep flock. Proc Biol Sci265, 1205–1210.[CrossRef][Google Scholar]