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PrP<sup>Sc</sup> from post-mortem brainstem or lymphoid tissues may be detected by Western immunoblot analysis <ref name="Farquhar et al., 1989">Farquhar CF, Somerville RA, Ritchie LA, 1989. Post-mortem immunodiagnosis of scrapie and bovine spongiform encephalopathy. Journal of Virological Methods, 24(1, 2):215-222; 21 ref.</ref>, <ref name="Stack et al., 1996"> Stack MJ, Keyes P, Scott AC, 1996. The diagnosis of bovine spongiform encephalopathy and scrapie by the detection of fibrils and the abnormal protein isoform. In: Baker H, Ridley RM, eds. Methods in molecular medicine: prion diseases. Totowa, New Jersey, USA: Humana Press, 85-103.</ref>, <ref name="Wadsworth et al., 2001 "> Wadsworth JDF, Joiner S, Hill AF, Campbell TA, Desbruslais M, Luthert PJ, Collinge J, 2001. Tissue distribution of protease resistant prion protein in variant Creutzfeldt-Jakob disease using a highly sensitive immunoblotting assay. Lancet, 358(9277):171-180.</ref> and immunohistochemistry (IHC) <ref name="Miller et al., 1993">Miller JM, Jenny AL, Taylor WD, Marsh RF, Rubenstein R, Race RE, 1993. Immunohistochemical detection of prion protein in sheep with scrapie. Journal of Veterinary Diagnostic Investigation, 5(3):309-316; 38 ref.</ref>, <ref name="Miller et al., 1994">Miller JM, Jenny AL, Taylor WD, Race RE, Ernst DR, Katz JB, Rubenstein R, 1994. Detection of prion protein in formalin-fixed brain by hydrated autoclaving immunohistochemistry for the diagnosis of scrapie in sheep. Journal of Veterinary Diagnostic Investigation, 6(3):366-368; 10 ref</ref>, <ref name="O'Rourke et al., 1998">O'Rourke KI, Baszler TV, Parish SM, Knowles DP, 1998. Preclinical detection of PrP in nictitating membrane lymphoid tissue of sheep. Veterinary Record, 142(18):489-491; 14 ref.</ref>, <ref name="Keulen et al., 1996; ">Keulen LJMvan, Schreuder BEC, Meloen RH, Mooij-Harkes G, Vromans MEW, Langeveld JPM, 1996. Immunohistochemical detection of prion protein in lymphoid tissues of sheep with natural scrapie. Journal of Clinical Microbiology, 34(5):1228-1231; 26 ref.</ref>, <ref name="Keulen et al., 1995">Keulen LJMvan, Schreuder BEC, Meloen RH, Berg MPvan den, Mooij-Harkes G, Vromans MEW, Langeveld JPM, 1995. Immunohistochemical detection and localization of prion protein in brain tissue of sheep with natural scrapie. Veterinary Pathology, 32(3):299-308; 35 ref.</ref>. Transmission to mice by injecting suspect tissue can be used to assay infectivity <ref name="OIE, 2000 " />. Tonsil <ref name="Schreuder et al., 1998">Schreuder BEC, Keulen LJMvan, Vromans MEW, Langeveld JPM, Smits MA, 1998. Tonsillar biopsy and PrP detection in the preclinical diagnosis of scrapie. Veterinary Record, 142(21):564-568; 31 ref. </ref>, <ref name="Schreuder et al., 1996 ">Schreuder BEC, Keulen LJMvan, Vromans MEW, Langeveld JPM, Smits MA, 1996. Preclinical test for prion diseases. Nature (London), 381(6583):563; 10 ref.</ref> and lymphoid biopsies <ref name=" Bender et al., 2004"> Bender S, Alverson J, Herrmann LM, O’Rourke KI, 2004. Histamine as an aid to biopsy of third eyelid lymphoid tissue in sheep. Veterinary Record, 154(21):662-663.</ref>, <ref name="Ikegami et al., 1991">Ikegami Y, Ito M, Isomura H, Momotani E, Sasaki K, Muramatsu Y, Ishiguro N, Shinagawa M, 1991. Pre-clinical and clinical diagnosis of scrapie by detection of PrP protein in tissues of sheep. Veterinary Record, 128(12):271-275; 16 ref.</ref>, <ref name="O'Rourke et al., 2000">O'Rourke KI, Baszler TV, Besser TE, Miller JM, Cutlip RC, Wells GAH, Ryder SJ, Parish SM, Hamir AN, Cockett NE, Jenny A, Knowles DP, 2000. Preclinical diagnosis of scrapie by immunohistochemistry of third eyelid lymphoid tissue. Journal of Clinical Microbiology, 38(9):3254-3259; 33 ref.</ref>, <ref name="O'Rourke et al., 1998">O'Rourke KI, Baszler TV, Miller JM, Spraker TR, Sadler-Riggleman I, Knowles DP, 1998. Monoclonal antibody F89/160.1.5 defines a conserved epitope on the ruminant prion protein. Journal of Clinical Microbiology, 36(6):1750-1755; 41 ref.</ref>, <ref name="Thuring et al., 2000 ">Thuring CMA, Sweeney T, McElroy MC, Weavers E, 2000. Suitability of protuberances on the third eyelids of sheep as a biopsy site for lymphoid follicles. Veterinary Record, 147(22):631-632; 10 ref.</ref> stained for PrP<sup>sc</sup> by using IHC have been used for preclinical scrapie screening.
PrP<sup>Sc</sup> from post-mortem brainstem or lymphoid tissues may be detected by Western immunoblot analysis <ref name="Farquhar et al., 1989">Farquhar CF, Somerville RA, Ritchie LA, 1989. Post-mortem immunodiagnosis of scrapie and bovine spongiform encephalopathy. Journal of Virological Methods, 24(1, 2):215-222; 21 ref.</ref>, <ref name="Stack et al., 1996"> Stack MJ, Keyes P, Scott AC, 1996. The diagnosis of bovine spongiform encephalopathy and scrapie by the detection of fibrils and the abnormal protein isoform. In: Baker H, Ridley RM, eds. Methods in molecular medicine: prion diseases. Totowa, New Jersey, USA: Humana Press, 85-103.</ref>, <ref name="Wadsworth et al., 2001 "> Wadsworth JDF, Joiner S, Hill AF, Campbell TA, Desbruslais M, Luthert PJ, Collinge J, 2001. Tissue distribution of protease resistant prion protein in variant Creutzfeldt-Jakob disease using a highly sensitive immunoblotting assay. Lancet, 358(9277):171-180.</ref> and immunohistochemistry (IHC) <ref name="Miller et al., 1993">Miller JM, Jenny AL, Taylor WD, Marsh RF, Rubenstein R, Race RE, 1993. Immunohistochemical detection of prion protein in sheep with scrapie. Journal of Veterinary Diagnostic Investigation, 5(3):309-316; 38 ref.</ref>, <ref name="Miller et al., 1994">Miller JM, Jenny AL, Taylor WD, Race RE, Ernst DR, Katz JB, Rubenstein R, 1994. Detection of prion protein in formalin-fixed brain by hydrated autoclaving immunohistochemistry for the diagnosis of scrapie in sheep. Journal of Veterinary Diagnostic Investigation, 6(3):366-368; 10 ref</ref>, <ref name="O'Rourke et al., 1998">O'Rourke KI, Baszler TV, Parish SM, Knowles DP, 1998. Preclinical detection of PrP in nictitating membrane lymphoid tissue of sheep. Veterinary Record, 142(18):489-491; 14 ref.</ref>, <ref name="Keulen et al., 1996; ">Keulen LJMvan, Schreuder BEC, Meloen RH, Mooij-Harkes G, Vromans MEW, Langeveld JPM, 1996. Immunohistochemical detection of prion protein in lymphoid tissues of sheep with natural scrapie. Journal of Clinical Microbiology, 34(5):1228-1231; 26 ref.</ref>, <ref name="Keulen et al., 1995">Keulen LJMvan, Schreuder BEC, Meloen RH, Berg MPvan den, Mooij-Harkes G, Vromans MEW, Langeveld JPM, 1995. Immunohistochemical detection and localization of prion protein in brain tissue of sheep with natural scrapie. Veterinary Pathology, 32(3):299-308; 35 ref.</ref>. Transmission to mice by injecting suspect tissue can be used to assay infectivity <ref name="OIE, 2000 " />. Tonsil <ref name="Schreuder et al., 1998">Schreuder BEC, Keulen LJMvan, Vromans MEW, Langeveld JPM, Smits MA, 1998. Tonsillar biopsy and PrP detection in the preclinical diagnosis of scrapie. Veterinary Record, 142(21):564-568; 31 ref. </ref>, <ref name="Schreuder et al., 1996 ">Schreuder BEC, Keulen LJMvan, Vromans MEW, Langeveld JPM, Smits MA, 1996. Preclinical test for prion diseases. Nature (London), 381(6583):563; 10 ref.</ref> and lymphoid biopsies <ref name=" Bender et al., 2004"> Bender S, Alverson J, Herrmann LM, O’Rourke KI, 2004. Histamine as an aid to biopsy of third eyelid lymphoid tissue in sheep. Veterinary Record, 154(21):662-663.</ref>, <ref name="Ikegami et al., 1991">Ikegami Y, Ito M, Isomura H, Momotani E, Sasaki K, Muramatsu Y, Ishiguro N, Shinagawa M, 1991. Pre-clinical and clinical diagnosis of scrapie by detection of PrP protein in tissues of sheep. Veterinary Record, 128(12):271-275; 16 ref.</ref>, <ref name="O'Rourke et al., 2000">O'Rourke KI, Baszler TV, Besser TE, Miller JM, Cutlip RC, Wells GAH, Ryder SJ, Parish SM, Hamir AN, Cockett NE, Jenny A, Knowles DP, 2000. Preclinical diagnosis of scrapie by immunohistochemistry of third eyelid lymphoid tissue. Journal of Clinical Microbiology, 38(9):3254-3259; 33 ref.</ref>, <ref name="O'Rourke et al., 1998">O'Rourke KI, Baszler TV, Miller JM, Spraker TR, Sadler-Riggleman I, Knowles DP, 1998. Monoclonal antibody F89/160.1.5 defines a conserved epitope on the ruminant prion protein. Journal of Clinical Microbiology, 36(6):1750-1755; 41 ref.</ref>, <ref name="Thuring et al., 2000 ">Thuring CMA, Sweeney T, McElroy MC, Weavers E, 2000. Suitability of protuberances on the third eyelids of sheep as a biopsy site for lymphoid follicles. Veterinary Record, 147(22):631-632; 10 ref.</ref> stained for PrP<sup>sc</sup> by using IHC have been used for preclinical scrapie screening.
Rapid tests for surveillance that have been approved by the EU include: Western blot test for the detection of the protease-resistant fragment PrP<sup>Res</sup>(Prionics Check test),
Rapid tests for surveillance that have been approved by the EU include: Western blot test for the detection of the protease-resistant fragment PrP<sup>Res</sup> (Prionics Check test),
Chemiluminescent ELISA test involving an extraction method and an ELISA technique, using an enhanced chemiluminescent reagent(Enfer test)and sandwich immunoassay for PrP<sup>Res</sup> carried out following denaturation and concentration steps (Bio-Rad test)<ref name="European Commission, 2001">European Commission, 2001. Commission Regulation (EC) No. 999/2001 of the European Parliament and of the Council of 22 May 2001 laying down rules for the prevention, control and eradication of certain transmissible spongiform encephalopathies. Official Journal of the European Communities, L 147:1-40.</ref>.
Chemiluminescent ELISA test involving an extraction method and an ELISA technique, using an enhanced chemiluminescent reagent (Enfer test) and sandwich immunoassay for PrP<sup>Res</sup> carried out following denaturation and concentration steps (Bio-Rad test) <ref name="European Commission, 2001">European Commission, 2001. Commission Regulation (EC) No. 999/2001 of the European Parliament and of the Council of 22 May 2001 laying down rules for the prevention, control and eradication of certain transmissible spongiform encephalopathies. Official Journal of the European Communities, L 147:1-40.</ref>.
'''Differential diagnosis''': Viral encephalomyelitides (pseudorabies or Aujeszky’s disease, rabies, maedi visna), Bacterial meningoencephalomyelitides (listeriosis), Pregnancy toxemia (ketosis), Hypocalcemis-hypomagnesemia, Toxins (mercury, lead, organophosphates, plant toxins) and Mange, lice, bacterial dermatitis <ref name="OIE, 2000" />.
'''Differential diagnosis''': Viral encephalomyelitides (pseudorabies or Aujeszky’s disease, rabies, maedi visna), Bacterial meningoencephalomyelitides (listeriosis), Pregnancy toxemia (ketosis), Hypocalcemis-hypomagnesemia, Toxins (mercury, lead, organophosphates, plant toxins) and Mange, lice, bacterial dermatitis <ref name="OIE, 2000" />.
==Control==
==Control==
Good husbandry and hygiene around lambing can greatly reduce the infectious load. It is recommended that individual straw bale pens are used which can be destroyed after each lambing and that contaminated bedding and placenta should be destroyed immediately. Infection can be minimised by maintaining a closed flock and only obtaining replacement ewes or breeding rams from scrapie-free flocks. Animals of resistant genotypes should be used for breeding to further minimize the risk of scrapie infection in a flock <ref name="CFIA, 2005"> Canadian Food Inspection Agency, 2005. Scrapie. http://www.inspection.gc.ca/english/anima/heasan/man/scrtre/scrtree.shtml, Accessed 7 March 2005.</ref>, <ref name="Dawson et al., 1998">Dawson M, Hoinville LJ, Hosie BD, Hunter N, 1998. Guidance on the use of PrP genotyping as an aid to the control of clinical scrapie. Veterinary Record, 142(23):623-625.</ref>, <ref name="European Commission, 2001" />; <ref name="US Department of Agriculture, 2005"> USDA, 2005. Scrapie program. http://www.aphis.usda.gov/vs/nahps/scrapie/, accessed 7 March 2005.</ref>. Genetic resistance to scrapie depends on the prion genotype of the sheep and on the strain of scrapie present. Genotypes of sheep resistant to one strain of scrapie may be susceptible to another strain but on the whole the ARR allele confers resistance in all breeds. The UK government control programme (National Scrapie Plan or NSP) was launched in 2001 and proposes to increase the frequency of the ARR allele in the UK sheep population <ref name="DEFRA, 2001"></ref>. Many countries use a combination of genetic selection, depopulation of infected sources and sourcing scrapie free flocks to control the spread of scrapie <ref name="US Department of Agriculture, 2005"> Department for Environment Food and Rural Affairs, 2001. National scrapie plan for Great Britain. Schemes brochure. DEFRA, 1-28.</ref> and <ref name="Thorgeirsdottir et al., 2002">Thorgeirsdottir S, Georgsson G, Reynisson E, Sigurdarson S, Palsdottir A, 2002. Search for healthy carriers of scrapie: an assessment of subclinical infection of sheep in an Icelandic scrapie flock by three diagnostic methods and correlation with PrP genotypes. Archives of Virology, 147(4):709-722; 31 ref.</ref>
Good husbandry and hygiene around lambing can greatly reduce the infectious load. It is recommended that individual straw bale pens are used which can be destroyed after each lambing and that contaminated bedding and placenta should be removed immediately. Infection can be minimised by maintaining a closed flock and only obtaining replacement ewes or breeding rams from scrapie-free flocks. Animals of resistant genotypes should be used for breeding to further minimize the risk of scrapie infection in a flock <ref name="CFIA, 2005">Canadian Food Inspection Agency, 2005. Scrapie. http://www.inspection.gc.ca/english/anima/heasan/man/scrtre/scrtree.shtml, Accessed 7 March 2005.</ref>, <ref name="Dawson et al., 1998">Dawson M, Hoinville LJ, Hosie BD, Hunter N, 1998. Guidance on the use of PrP genotyping as an aid to the control of clinical scrapie. Veterinary Record, 142(23):623-625.</ref>, <ref name="European Commission, 2001" />, <ref name="US Department of Agriculture, 2005"> USDA, 2005. Scrapie program. http://www.aphis.usda.gov/vs/nahps/scrapie/, accessed 7 March 2005.</ref>. Genetic resistance to scrapie depends on the prion genotype of the sheep and on the strain of scrapie present. Genotypes of sheep resistant to one strain of scrapie may be susceptible to another strain but on the whole the ARR allele confers resistance in all breeds. The UK government control programme (National Scrapie Plan or NSP) was launched in 2001 and proposes to increase the frequency of the ARR allele in the UK sheep population <ref name="DEFRA, 2001"></ref>. Many countries use a combination of genetic selection, depopulation of infected sources and sourcing scrapie free flocks to control the spread of scrapie <ref name="US Department of Agriculture, 2005"> Department for Environment Food and Rural Affairs, 2001. National scrapie plan for Great Britain. Schemes brochure. DEFRA, 1-28.</ref> and <ref name="Thorgeirsdottir et al., 2002">Thorgeirsdottir S, Georgsson G, Reynisson E, Sigurdarson S, Palsdottir A, 2002. Search for healthy carriers of scrapie: an assessment of subclinical infection of sheep in an Icelandic scrapie flock by three diagnostic methods and correlation with PrP genotypes. Archives of Virology, 147(4):709-722; 31 ref.</ref>
Meat- and bone meal-contaminated feeds have not been shown to be involved in scrapie transmission, but prohibiting the use of feeds that contain ruminant animal products in sheep and goats is a prudent measure. In the UK, a feed ban was issued in 1988 prohibiting the feeding of ruminant-derived meat and bone meal to ruminants (HMSO, 2002) and was adopted by the EU in 1994 and USA in 1997 <ref name="European Commission, 2001" />; <ref name="FDA, 1997"> Food and Drug Administration, 1997. 21 CFR Part 589 [Docket No. 96N–0135] RIN 0910–AA91 substances prohibited from use in animal food or feed; animal proteins prohibited in ruminant feed. DHHS, 30935-30978.</ref>.
Meat- and bone meal-contaminated feeds have not been shown to be involved in scrapie transmission, but prohibiting the use of feeds that contain ruminant animal products in sheep and goats is a prudent measure. In the UK, a feed ban was issued in 1988 prohibiting the feeding of ruminant-derived meat and bone meal to ruminants (HMSO, 2002) and was adopted by the EU in 1994 and USA in 1997 <ref name="European Commission, 2001" />; <ref name="FDA, 1997"> Food and Drug Administration, 1997. 21 CFR Part 589 [Docket No. 96N–0135] RIN 0910–AA91 substances prohibited from use in animal food or feed; animal proteins prohibited in ruminant feed. DHHS, 30935-30978.</ref>.