Difference between revisions of "Scrapie"

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Also known as: '''''TSE – Transmissible spongiform encephalopathy''''', '''''Paraplexia enzootica ovium'''''  
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Also known as: '''''Transmissible Spongiform Encephalopathy of Sheep — TSE — Paraplexia enzootica ovium'''''  
 
  
 
==Introduction==  
 
==Introduction==  
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Scrapie was first described in the UK in 1732 <ref name=" McGowan, 1922 "> McGowan JP, 1922. Scrapie in sheep. Scottish Journal of Agriculture, 5:365-375.</ref>, <ref name=" Pattison, 1988 "> Pattison IH, 1988. Fifty years with scrapie: a personal reminiscence. Veterinary Record, 123(26-27):661-666; 60 ref.</ref>,  and recognised as an infectious disease in 1936 <ref name="Chelle, 1942"> Chelle PL, 1942. Un cas de tremblante chez la chèvre. Bulletin Académie Vétérinaire de France, 15:294-295.</ref>, <ref name="Poser, 2002">Poser CM, 2002. Notes on the history of the prion diseases. Part I. Clinical Neurology and Neurosurgery, 104(1):1-9.</ref>.  It is a progressive, fatal and non-febrile neurological disorder affecting sheep and goats.  It belongs to a group of diseases called transmissible spongiform encephalopathy (TSE) and other TSE’s include Creutzfeldt-Jakob disease in humans, BSE, chronic wasting disease (CWD) in elk and deer, transmissible mink encephalopathy and feline spongiform encephalopathy has been found within cats in the UK. The disease is believed to be caused by a conformational change in the prion (PrP).  A prion is a protein that occurs normally in the nervous and lymphoreticular tissues.  It is only when the prion changes conformation into a protease-resistant protein  PrP<sup>sc</sup> that it causes degeneration of neurological tissue. The disease causes astrocyte proliferation and then vacuolization of neurons but demyelination does not occur <ref name=" Dandoy-Dron et al., 1998 ">. Dandoy-Dron F, Guillo F, Benboudjema L, Deslys JP, Lasmézas C, Dormont D, Tovey MG, Dron M, 1998. Gene expression in scrapie. Cloning of a new scrapie-responsive gene and the identification of increased levels of seven other mRNA transcripts. Journal of Biological Chemistry, 273(13):7691-7697,48 ref.</ref>. The abnormal protein is thought to act as a catalyst to convert more of the host’s protein into this abnormal form.  The disease has been notifiable in the EU since 1993 but unlike BSE there is no evidence to suggest that scrapie is a risk to human health <ref name="Brown et al., 1987">Brown P, Cathala F, Raubertas RF, Gajdusek DC, Castaigne P, 1987. The epidemiology of Creutzfeldt-Jakob disease: conclusion of a 15-year investigation in France and review of the world literature. Neurology, 37(6):895-904.</ref>, <ref name="Harries et al.,1988">Harries JR, Knight R, Will RG, Cousens SN, Smith PG, Mathews WB, 1988. Creutzfeldt-Jakob disease in England and Wales, 1980-1984: a case-control study of potential risk factors. Journal of Neurology Neurosurgery and Psychiatry, 51(9):1113-1119.</ref>,<ref name="Kondo and Kuriowa, 1982">Kondo K, Kuriowa Y, 1982. A case control study of Creutzfeldt-Jakob disease: association with physical injuries. Annals of Neurology, 11(4):377-381.</ref>, <ref name="WHO, 1999">World Health Organization, 1999. WHO consultation on public health and animal transmissible spongiform encephalopathies: epidemiology, risk and research requirements, with the participation of the Office International des Epizooties. http://www.who.int/csr/resources/publications/bse/WHO_CDS_CSR_APH_2000,Accessed 7 March 2005. http://www.who.int/csr/resources/publications/bse/en/whocdscsraph20002.pdf.</ref>. Studies on the spread of scrapie infectivity have suggested that after oral intake, PrPSc first accumulates in Peyer’s patches of the small intestine, gut-associated lymphoid tissues (GALT) and ganglia of the enteric nervous system <ref name="Beekes and McBride,2000">Beekes M, McBride PA, 2000. Early accumulation of pathological PrP in the enteric nervous system and gut-associated lymphoid tissue of hamsters orally infected with scrapie. Neuroscience Letters, 278(3):181-184.</ref>,<ref name="Beekes et al., 1998">Beekes M, McBride PA, Baldauf E, 1998. Cerebral targeting indicates vagal spread of infection in hamsters fed with scrapie. Journal of General Virology, 79(3):601-607; 20 ref.</ref>, <ref name="Heggebø et al., 2000">Heggebø R, Press CM, Gunnes G, Lie KaiInge, Tranulis MA, Ulvund M, Groschup MH, Landsverk T, 2000. Distribution of prion protein in the ileal Peyer's patch of scrapie-free lambs and lambs naturally and experimentally exposed to the scrapie agent. Journal of General Virology, 81(9):2327-2337; 2 pp. of ref.</ref>, <ref name="Kimberlin and Walker, 1989">Kimberlin RH, Walker CA, 1989. Pathogenesis of scrapie in mice after intragastric infection. Virus Research, 12(3):213-220; 32 ref.</ref>, <ref name="Keulen et al., 1999">Keulen LJMvan, Schreuder BEC, Vromans MEW, Langeveld JPM, Smits MA, 1999. Scrapie-associated prion protein in the gastro-intestinal tract of sheep with natural scrapie. Journal of Comparative Pathology, 121(1):55-63; 24 ref.</ref>.  PrPSc then moves onward to the tonsil, spleen, retropharyngeal lymph nodes, mesenteric lymph nodes, and peripheral nervous tissue <ref name=" Mabbott and Bruce, 2001 ">Mabbott NA, Bruce ME, 2001. The immunobiology of TSE diseases. Journal of General Virology, 82(10):2307-2318; many ref.</ref>, <ref name="Maignien et al., 1999 ">Maignien T, Lasmézas CI, Beringue V, Dormont D, Deslys JP, 1999. Pathogenesis of the oral route of infection of mice with scrapie and bovine spongiform encephalopathy agents. Journal of General Virology, 80(11):3035-3042; 32 ref.</ref>,<ref name="Press et al., 2004"> Press CM, Heggebø R, Espenes A, 2004. Involvement of gut-associated lymphoid tissue of ruminants in the spread of transmissible spongiform encephalopathies. Advanced Drug Delivery Reviews, 56(6):885-899.</ref>. PrPSc eventually spreads to most lymph nodes and the central nervous system (CNS). PrPSc can be found in the lymphoreticular system tissues for months before it is found in the brain <ref name="Eklund et al., 1967">Eklund CM, Kennedy RC, Hadlow WJ, 1967. Pathogenesis of scrapie virus infection in the mouse. Journal of Infectious Diseases, 117(1):15-22.</ref>, <ref name="Hadlow et al., 1974"> Hadlow W, Eklund CM, Kennedy RC, Jackson TA, Whitford HW, Boyle CC, 1974. Course of experimental scrapie virus infection in the goat. Journal of Infectious Diseases, 129(5):559-567.</ref>, <ref name="Hadlow et al., 1982"> Hadlow W, Kennedy RC, Race RE, 1982. Natural infection of Suffolk sheep with scrapie virus. Journal of Infectious Diseases, 146(5):657-664.</ref>, <ref name="Hadlow et al., 1980"> Hadlow WJ, Kennedy RC, Race RE, Eklund CM, 1980. Virologic and neurohistologic findings in dairy goats affected with natural scrapie. Veterinary Pathology, 17(2):187-199.</ref>; <ref name="Hadlow et al., 1979"> Hadlow WJ, Race RE, Kennedy RC, Eklund CM, 1979. Natural infection of sheep with scrapie virus. Slow transmissible diseases of the nervous system. Volume 2., 3-12; 5 ref.</ref>. Affected animals may live one to six months after onset of clinical signs <ref name="Capucchio et al., 2001">Capucchio MT, Guarda F, Pozzato N, Coppolino S, Caracappa S, Marco Vdi, 2001. Clinical signs and diagnosis of scrapie in Italy: a comparative study in sheep and goats. Journal of Veterinary Medicine. Series A, 48(1):23-31; 11 ref.</ref>, <ref name="Foster et al., 2001a "> Foster J, Goldmann W, Parnham D, Chong A, Hunter N, 2001a. Partial dissociation of PrP deposition and vacuolation in the brains of scrapie and BSE experimentally affected goats. Journal of General Virology, 82(1):267-273; 30 ref.</ref> , <ref name="Foster et al., 2001b ">Foster JD et al., 2001b. Clinical signs, histopathology and genetics of experimental transmission of BSE and natural scrapie to sheep and goats. Vet. Rec., 148:165-171.</ref>,<ref name="Foster et al., 2001c "> Foster JD, Parnham D, Chong A, Goldmann W, Hunter N, 2001c. Clinical signs, histopathology and genetics of experimental transmission of BSE and natural scrapie to sheep and goats. Veterinary Record, 148(6):165-171, 22 .</ref>, <ref name="USDA, 2005."> USDA, 2005. Scrapie program. http://www.aphis.usda.gov/vs/nahps/scrapie/, accessed 7 March 2005. </ref>.
  
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Scrapie is a '''progressive, fatal''' and '''non-febrile neurological''' disorder affecting '''sheep''' and '''goats'''. It belongs to a group of diseases called [[:Category:Transmissible Spongiform Encephalopathies|transmissible spongiform encephalopathy (TSE)]] and [[Prion Disease|other TSE’s]] include Creutzfeldt-Jakob disease in humans, [[BSE]], chronic wasting disease (CWD) in elk and deer, transmissible mink encephalopathy and feline spongiform encephalopathy has been found within cats in the UK.  
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The original source of disease is thought to have come from imported Merino sheep from Spain  <ref name="Parry and Oppenheimer, 1983">Parry HB, Oppenheimer DR, 1983. Scrapie disease in sheep. Historical, clinical, epidemiological, pathological and practical aspects of the natural disease. Scrapie disease in sheep. Historical, clinical, epidemiological, pathological and practical aspects of the natural disease., xvi + 192pp., 341 ref.</ref>, <ref name="Stockman, 1913 " />, and spread through the movement of of scrapie-infected preclinical sheep <ref name="Brash, 1952"> Brash AG, 1952. Scrapie in imported sheep in New Zealand. New Zealand Veterinary Journal, 1(2):27-30.</ref>, <ref name="Bull and Murnane, 1958"> Bull LB, Murnane D, 1958. An outbreak of scrapie in British sheep imported into Victoria. Australian Veterinary Journal, 34:213-215.</ref>, <ref name="Cooper, 1973"> Cooper JE, 1973. A report of scrapie in sheep in Kenya. British Veterinary Journal, 129(2):13-16.</ref>, <ref name="Parry and Oppenheimer, 1983" />, <ref name="Merwe, 1966"> Merwe GF van der, 1966. The first occurrence of scrapie in the Republic of South Africa. Journal of South African Veterinary Medical Association, 37(4):415-418.</ref>. Scrapie is now endemic throughout Europe and most other continents <ref name="Detwiler and Baylis, 2003"> Detwiler LA, Baylis M, 2003. The epidemiology of scrapie. Revue Scientifique et Technique Office International des Epizooties, 22(1):121-143.</ref>, <ref name="OIE, 2000"> OIE, 2000. Scrapie. OIE Manual of Standards for diagnostic tests and vaccines. 4 ed. Paris, France: Office International des Epizooties, 873-880.</ref>. It has also been reported in goats <ref name="Andrews et al., 1992">Andrews AH, Laven R, Matthews JG, 1992. Clinical observations on four cases of scrapie in goats. Veterinary Record, 130(5):101, 9 ref.</ref>, <ref name="Brotherston et al., 1968"> Brotherston JG, Renwick CC, Stamp JT, Zlotnik I, 1968. Spread of scrapie by contact to goats and sheep. Journal of Comparative Pathology, 78(1):9-17.</ref>; <ref name="Capucchio et al., 1998">Capucchio MT, Guarda F, Isaia MC, Caracappa S, DiMarco V, 1998. Natural occurence of scrapie in goats in Italy. Veterinary Record, 143(16):452-453.</ref>, <ref name="Chelle, 1942"/>, <ref name="Fankhauser et al., 1982"> Fankhauser R, Vandevelde M, Zwahlen R, 1982. Scrapie in Switzerland? Schweizer Archiv Für Tierheilkunde, 124(5):227-232.</ref>;<ref name="Harcourt, 1974"> Harcourt RA, 1974. Naturally occurring scrapie in goats. Veterinary Record, 94(22):504.</ref>, <ref name="Hourrigan et al., 1979"> Hourrigan JL, Klingsporn AI, Clark WW, DeCamp M, 1979. Epidemiology of scrapie in the US. In: Prusiner SB, Hadlow W, eds. Slow transmissible diseases of the nervous system. New York: Academic Press, 331-356.</ref>, <ref name="Leontides et al., 2000"> Leontides S et al., 2000. A survey of more than 11 years of neurologic diseases of ruminants with special reference to transmissible spongiform encephalopathies (TSEs) in Greece. Journal of Veterinary Medicine. Series B, 47:303-309.</ref>, <ref name="Stemshorn, 1975"> Stemshorn BW, 1975. Un cas de tremblante naturelle chez une chévre. Canadian Veterinary Journal, 16(3):84-86.</ref>, <ref name="Toumazos, 1991"> Toumazos P, 1991. Scrapie in Cyprus. British Veterinary Journal, 147(2):147-154; 11 ref.</ref>, <ref name="Toumazos and Alley, 1989. "> Toumazos P, Alley MR, 1989. Scrapie in goats in Cyprus. New Zealand Veterinary Journal, 37(4):160-162; 11 ref.</ref>. Only Australia and New Zealand are recognized as being currently free of scrapie.
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The disease is believed to be caused by a '''conformational change in the prion (PrP)'''. A prion is a protein that occurs normally in the nervous and lymphoreticular tissues. It is only when the prion changes conformation into a protease-resistant protein  PrP<sup>sc</sup> that it causes degeneration of neurological tissue. The disease causes astrocyte proliferation and then vacuolization of neurons but demyelination does not occur <ref name=" Dandoy-Dron et al., 1998 ">. Dandoy-Dron F, Guillo F, Benboudjema L, Deslys JP, Lasmézas C, Dormont D, Tovey MG, Dron M (1998) '''Gene expression in scrapie. Cloning of a new scrapie-responsive gene and the identification of increased levels of seven other mRNA transcripts.''''' Journal of Biological Chemistry,'' 273(13):7691-7697,48 ref.</ref>. The abnormal protein is thought to act as a catalyst to convert more of the host’s protein into this abnormal form.
 
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The disease has been '''notifiable in the EU''' since 1993 but unlike BSE there is no evidence to suggest that scrapie is a risk to human health <ref name="Brown et al., 1987">Brown P, Cathala F, Raubertas RF, Gajdusek DC, Castaigne P (1987) '''The epidemiology of Creutzfeldt-Jakob disease: conclusion of a 15-year investigation in France and review of the world literature. '''''Neurology, ''37(6):895-904.</ref>, <ref name="Harries et al.,1988">Harries JR, Knight R, Will RG, Cousens SN, Smith PG, Mathews WB (1988) '''Creutzfeldt-Jakob disease in England and Wales, 1980-1984: a case-control study of potential risk factors.''''' Journal of Neurology Neurosurgery and Psychiatry,'' 51(9):1113-1119.</ref>,<ref name="Kondo and Kuriowa, 1982">Kondo K, Kuriowa Y (1982)''' A case control study of Creutzfeldt-Jakob disease: association with physical injuries. '''''Annals of Neurology, 11(4):377-381.</ref>, <ref name="WHO, 1999">World Health Organization, 1999. WHO consultation on public health and animal transmissible spongiform encephalopathies: epidemiology, risk and research requirements, with the participation of the Office International des Epizooties. http://www.who.int/csr/resources/publications/bse/WHO_CDS_CSR_APH_2000,Accessed 7 March 2005. http://www.who.int/csr/resources/publications/bse/en/whocdscsraph20002.pdf.</ref>.  
 
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Scrapie is thought to have come from imported Merino sheep from Spain and has since spread through the movement of infected sheep. Only Australia and New Zealand are recognized as being currently free of scrapie.
 
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==Pathophysiology==
 
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Studies have suggested that after ingestion, PrP<sup>sc</sup> first accumulates in [[Peyer's Patches - Anatomy & Physiology|Peyer’s patches]] of the small intestine, [[Regional Lymphoid Tissue - Anatomy & Physiology#Structure|gut-associated lymphoid tissues (GALT)]] and ganglia of the enteric nervous system <ref name="Beekes and McBride,2000">Beekes M, McBride PA (2000) '''Early accumulation of pathological PrP in the enteric nervous system and gut-associated lymphoid tissue of hamsters orally infected with scrapie. '''''Neuroscience Letters,'' 278(3):181-184.</ref>,<ref name="Beekes et al., 1998">Beekes M, McBride PA, Baldauf E (1998) '''Cerebral targeting indicates vagal spread of infection in hamsters fed with scrapie.''''' Journal of General Virology,'' 79(3):601-607; 20 ref.</ref>, <ref name="Heggebø et al., 2000">Heggebø R, Press CM, Gunnes G, Lie KaiInge, Tranulis MA, Ulvund M, Groschup MH, Landsverk T (2000) '''Distribution of prion protein in the ileal Peyer's patch of scrapie-free lambs and lambs naturally and experimentally exposed to the scrapie agent.''''' Journal of General Virology,'' 81(9):2327-2337; 2 pp. of ref.</ref>, <ref name="Kimberlin and Walker, 1989">Kimberlin RH, Walker CA (1989) '''Pathogenesis of scrapie in mice after intragastric infection.''''' Virus Research,'' 12(3):213-220; 32 ref.</ref>, <ref name="Keulen et al., 1999">Keulen LJMvan, Schreuder BEC, Vromans MEW, Langeveld JPM, Smits MA (1999) '''Scrapie-associated prion protein in the gastro-intestinal tract of sheep with natural scrapie.''''' Journal of Comparative Pathology,'' 121(1):55-63; 24 ref.</ref>, it then spreads throughout the [[Lymph Nodes - Anatomy & Physiology|lymph nodes]], [[Tonsils - Anatomy & Physiology|tonsils]], [[Spleen - Anatomy & Physiology|spleen]], and into the [[PNS Structure - Anatomy & Physiology|peripheral nervous tissue]]. It is finally found in the brain several months later. It is extremely durable and is able to withstand high temperatures and concentrations of formaldehyde.
 
  
 
==Signalment==  
 
==Signalment==  
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Scrapie affects the majority of sheep between '''3 and 5 years of age''' and has a '''long incubation period''' of two to five years. Unlike BSE, scrapie is influenced by breed and genetic variation of the PrP gene within sheep populations, which can affect the infectivity and incubation period of the scrapie.  
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Scrapie has a long incubation period of two to five years <ref name="Stockman, 1913"/> and affects the majority of sheep between 3 and 5 years of age.  It is able to withstand a high degree of heat and high concentrations of formaldehyde <ref name="Pattison, 1965"> Pattison IH, 1965. Resistance of the scrapie agent to formalin. Journal of Comparative Pathology, 75(Apr):159-164.</ref>; <ref name="Stamp et al., 1959 "> Stamp JJB, Zlotnik I, Mackay J, Smith W, 1959. Further studies on scrapie. Journal of Comparative Pathology, 69(Jul):268-80. </ref> and unlike BSE is influenced by breed and genetic variations among sheep influence infectivity and the incubation period of scrapie.  Research has shown that  amino acid changes in at least three locations on the PrP gene (codons 136, 154, and 171), have been shown to confer increased or decreased susceptibility to scrapie <ref name="Belt et al., 1995">Belt PBGM, Muileman IH, Schreuder BEC, Bos-de Ruijter J, Gielkens ALJ, Smits MA, 1995. Identification of five allelic variants of the sheep PrP gene and their association with natural scrapie. Journal of General Virology, 76(3):509-517; 33 ref. </ref>; <ref name="Billinis et al., 2004"> Billinis C, Psychas V, Leontides L, Spyrou V, Argyroudis S, Vlemmas I, Leontides S, Sklaviadis T, Papadopoulos O, 2004. Prion protein gene polymorphisms in healthy and scrapie-affected sheep in Greece. Journal of General Virology, 85(2):547-554.</ref>; <ref name="Clouscard et al., 1995">Clouscard C, Beaudry P, Elsen JM, Milan D, Dussaucy M, Bounneau C, Schelcher F, Chatelain J, Launay JM, Laplanche JL, 1995. Different allelic efforts of the codons 136 and 171 of the prion protein gene in sheep with natural scrapie. Journal of General Virology, 76(8):2097-2101; 19 ref. </ref>; <ref name="Elsen et al., 1999">Elsen JM, Amigues Y, Schelcher F, Ducrocq V, Andreoletti O, Eychenne F, Khang JVT, Poivey JP, Lantier F, Laplanche JL, 1999. Genetic susceptibility and transmission factors in scrapie: detailed analysis of an epidemic in a closed flock of Romanov. Archives of Virology, 144(3):431-445; 34 ref.</ref>; <ref name="Goldmann et al., 1991">; <ref name="Goldmann et al., 1990">Goldmann W, Hunter N, Benson G, Foster JD, Hope J, 1991. Different scrapie-associated fibril proteins (PrP) are encoded by lines of sheep selected for different alleles of the Sip gene. Journal of General Virology, 72(10):2411-2417; 46 ref.</ref>; <ref name="Goldmann et al., 1994a">Goldmann W, Hunter N, Smith G, Foster J, Hope J, 1994a. PrP genotype and agent effects in scrapie: change in allelic interaction with different isolates of agent in sheep, a natural host of scrapie. Journal of General Virology, 75(5):989-995; 29 ref. </ref>, <ref name="Goldmann et al., 1994b"> Goldmann W, Hunter N, Smith G, Foster J, Hope J, 1994b. PrP genotypes and the Sip gene in Cheviot sheep form the basis for scrapie strain typing in sheep. Annals of the New York Academy of Sciences, 724(Jun 6):296-299. </ref> , <ref name="Hunter and Cairns, 1998">Hunter N, Cairns D, 1998. Scrapie-free Merino and Poll Dorset sheep from Australia and New Zealand have normal frequencies of scrapie-susceptible PrP genotypes. Journal of General Virology, 79(8):2079-2082; 17 ref. </ref>,; <ref name="Hunter et al., 1997a ">Hunter N, Goldmann W, Foster JD, Cairns D, Smith G, 1997a. Natural scrapie and PrP genotype: case-control studies in British sheep. Veterinary Record, 141(6):137-140; 15 ref.</ref>,, <ref name="Hunter et al., 1997b ">Hunter N, Moore L, Hosie BD, Dingwall WS, Greig A, 1997b. Association between natural scrapie and PrP genotype in a flock of Suffolk sheep in Scotland. Veterinary Record, 140(3):59-63; 20 ref.</ref>,, <ref name="Hunter et al., 1997c ">Hunter N, Cairns D, Foster JD, Smith G, Goldmann W, Donnelly K, 1997c. Is scrapie solely a genetic disease?. Nature (London), 386(6621):137; 10 ref.</ref>,,  <ref name="Hunter et al., 1991; ">Hunter N, Foster JD, Benson G, Hope J, 1991. Restriction fragment length polymorphisms of the scrapie-associated fibril protein (PrP) gene and their association with susceptibility to natural scrapie in British sheep. Journal of General Virology, 72(6):1287-1292; 19 ref.</ref>, <ref name= "Hunter et al., 1996">Hunter N, Foster JD, Goldmann W, Stear MJ, Hope J, Bostock C, 1996. Natural scrapie in a closed flock of Cheviot sheep occurs only in specific PrP genotypes. Archives of Virology, 141(5):809-824; 32 ref.</ref>,; <ref name="Hunter et al., 1992">Hunter N, Foster JD, Hope J, 1992. Natural scrapie in British sheep: breeds, ages and PrP gene polymorphisms. Veterinary Record, 130(18):389-392; 16 ref.</ref>,; <ref name="Hunter et al., 1993">Hunter N, Goldmann W, Benson G, Foster JD, Hope J, 1993. Swaledale sheep affected by natural scrapie differ significantly in PrP genotype frequencies from healthy sheep and those selected for reduced incidence of scrapie. Journal of General Virology, 74(6):1025-1031; 24 ref.</ref>,<ref name="Hunter et al., 1994">Hunter N, Goldmann W, Smith G, Hope J, 1994. The association of a codon 136 PrP gene variant with the occurrence of natural scrapie. Archives of Virology, 137(1/2):171-177; 22 ref.</ref>,<ref name="Ikeda et al., 1995">Ikeda T, Horiuchi M, Ishiguro N, Muramatsu Y, Kai-Uwe GD, Shinagawa M, 1995. Amino acid polymorphisms of PrP with reference to onset of scrapie in Suffolk and Corriedale sheep in Japan. Journal of General Virology, 76(10):2577-2581; 18 ref.</ref>,<ref name="Thorgeirsdottir et al., 1999">Thorgeirsdottir S, Sigurdarson S, Thorisson HM, Georgsson G, Palsdottir A, 1999. PrP gene polymorphism and natural scrapie in Icelandic sheep. Journal of General Virology, 80(9):2527-2534; 32 ref.</ref>,<ref name="Tranulis et al., 1999">Tranulis MA, Osland A, Bratberg B, Ulvund MJ, 1999. Prion protein gene polymorphisms in sheep with natural scrapie and healthy controls in Norway. Journal of General Virology, 80(4):1073-1077; 23 ref.</ref>, <ref name="Westaway et al., 1994"> Westaway D, Zuliani V, Mirenda Cooper C, Da Costa M, Neuman S, Jenny AL, Detwiler L, Prusiner SB, 1994. Homozygosity for prion protein alleles encoding glutamine-171 renders sheep susceptible to natural scrapie. Genes and Development, 8(8):959-969.</ref>,.  The disease has been shown to be effectively transmitted during lambing <ref name="Dickinson et al., 1974"> Dickinson AG, Stamp JT, Renwick CC, 1974. Maternal and lateral transmission of scrapie in sheep. Journal of Comparative Pathology, 84(1):19-25.</ref>; <ref name="Hourrigan et al., 1979 " />  as placenta and possibly the placental fluids are thought to be a source of infection <ref name="Andréoletti et al., 2002">Andréoletti O, Lacroux C, Chabert A, Monnereau L, Tabouret G, Lantier F, Berthon P, Eychenne F, Lafond-Benestad S, Elsen JM, Schelcher F, 2002. PrP accumulation in placentas of ewes exposed to natural scrapie: influence of foetal PrP genotype and effect on ewe-to-lamb transmission. Journal of General Virology, 83(10):2607-2616; 48 ref. </ref>; <ref name="Onodera et al., 1993"> Onodera T, Ikeda T, Muramatsu Y, Shinagawa M, 1993. Isolation of scrapie agent from the placenta of sheep with natural scrapie in Japan. Microbiology and Immunology, 37(4):311-316. </ref>; <ref name="Race et al., 1998">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. Journal of Infectious Diseases, 178(4):949-953; 29 ref. </ref>; <ref name="Tuo et al., 2002">Tuo WB, O'Rourke KI, Zhuang DY, Cheevers WP, Spraker TR, Knowles DP, 2002. Pregnancy status and fetal prion genetics determine PrP accumulation in placentomes of scrapie-infected sheep. Proceedings of the National Academy of Sciences of the United States of America, 99(9):6310-6315; 31 ref. </ref>; <ref name="Tuo et al., 2001">Tuo W, Zhuang D, Knowles DP, Cheevers WP, Sy M-S, O’Rourke K, 2001. PrP-C and PrP-Sc at the fetal-maternal interface. Journal of Biological Chemistry, 276(21):18229-18234.
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</ref> and experimental studies have shown that oral dosing of infected placenta can spread the disease in sheep and goats <ref name="Pattison et al., 1972"> Pattison IH, Hoare MN, Jebbett JN, 1972. Spread of scrapie to sheep and goats by oral dosing with foetal membranes from scrapie-affected sheep. Veterinary Record, 90(17):465-468.</ref>.
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The disease has been shown to be effectively '''transmitted during lambing''' <ref name="Dickinson et al., 1974"> Dickinson AG, Stamp JT, Renwick CC (1974) '''Maternal and lateral transmission of scrapie in sheep.''''' Journal of Comparative Pathology,'' 84(1):19-25.</ref>, <ref name="Hourrigan et al., 1979">Hourrigan JL, Klingsporn AI, Clark WW, DeCamp M (1979) '''Epidemiology of scrapie in the US. In: Prusiner SB, Hadlow W, eds. Slow transmissible diseases of the nervous system.''''' New York: Academic Press,'' 331-356.</ref>, and experimental studies have shown that the ingestion of infected placenta can spread the disease in sheep and goats <ref name="Pattison et al., 1972">Pattison IH, Hoare MN, Jebbett JN (1972) '''Spread of scrapie to sheep and goats by oral dosing with foetal membranes from scrapie-affected sheep. '''''Veterinary Record,'' 90(17):465-468.</ref>.
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==Clinical Signs==  
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Early clinical signs may include subtle behavioural changes such as staring or fixed gaze, teeth grinding (bruxism), fine tremor, and hyperaesthesia to sound or sudden movements. Affected animals may later become intolerant to exercise and develop ataxia (awkwardness at turning, swaying of the hindquarters and some gait abnormalities such as a high stepping gait in the forelimbs or a bunny hopping gait in the hindlimbs). Some sheep have intense pruritis that leads to compulsive rubbing, nibbling at the skin, or scraping against fixed objects and may lead to wool loss (especially over the hindquarters and lateral thorax). A characteristic lip smacking or nibbling reflex can often be elicited by scratching over the lumbar region. In later stages there can be significant weight loss even without a noticeable decrease in appetite, weakness, recumbency, and death. <ref name="Bradley, 1997"> Bradley R, 1997. Animal prion diseases. In: Collinge J, Palmer MS, eds. Prion diseases. Oxford, UK: Oxford University Press, 89-129.</ref>, <ref name="Dickinson, 1976"> Dickinson AG, 1976. Scrapie in sheep and goats. Frontiers in Biology, 44:209-241</ref>; <ref name="Kimberlin, 1981"> Kimberlin RH, 1981. Scrapie. British Medical Journal, 137:105-112.</ref>; <ref name="Palmer, 1976; "> Palmer AC, 1976. Scrapie. In: Palmer AC, ed. Introduction to animal neurology. Oxford, UK: Blackwell Scientific Publications, 177-178.</ref>, <ref name=" Parry and Oppenheimer, 1983" />; <ref name="Radostits et al., 2000"></ref>.  It is important to note that some scrapie-infected sheep may appear healthy until stressed by  transport, shearing, or pregnancy <ref name="Detwiler and Baylis, 2003" />.
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==Clinical Signs==
 
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[[File:Sheep-scrapie1.jpg|thumb|200px|right|Picture from the rear shows bare patches from rubbing (Sourced from Wiki Commons)]]
 
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Early clinical signs may include subtle '''behavioural and neurological changes'''. Sheep often have a '''fixed gaze''', and suffer from bruxism, fine tremors, and hyperaesthesia to sound or sudden movements. Affected animals may later become exercise intolerant and develop '''progressive ataxia'''.  Sheep often find difficulty in turning, sway on their hind hindquarters and have gait abnormalities such as a high stepping gait in the forelimbs or a bunny hopping gait in the hind limbs. Some sheep have '''intense pruritus''' that leads to compulsive rubbing, nibbling at the skin, or scraping against fixed objects. Wool loss is typically seen over the hindquarters and lateral thorax. Lip smacking or '''nibbling reflex''' can often be elicited by scratching over the lumbar region, which is characteristic of scrapie. Significant weight loss with or without a decrease in appetite, weakness, recumbency, and death are all seen within the later stages of the disease.  
 
  
 
==Diagnosis==
 
==Diagnosis==
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[[File:Scrapie lymph node immunoglobulin labeling.png|thumb|200px|right|Immunoglobulin in normal(a) and scrapie-affected (b)follicles - with light microscopy.]]
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A pre-emptive diagnosis of scrapie may be made from the above clinical signs combined with history and confirmed with laboratory tests. As there is no immune or inflammatory response there are no serological test available for scrapie <ref name="Kasper et al., 1982"> Kasper K, Bowman K, Panitch H, Prusiner SB, 1982. Immunological studies of scrapie infection. Journal of Neuroimmunology, 3(3):187-201.</ref>; <ref name="Porter et al., 1973."> Porter D, Porter H, Cox N, 1973. Failure to demonstrate a humoral immune response to scrapie infection in mice. Journal of Immunology, 111(5):1407-1410.</ref>
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A pre-emptive diagnosis of scrapie may be made from the above clinical signs and history. There are no serological test available for scrapie, as is does not evoke an immune or inflammatory response.
+
Pathologic lesions are confined to the CNS. Histology (immunohistochemistry) usually shows vacuolation and an accumulation of prion proteins in various parts of the CNS (medulla, pons, midbrain, and spinal cord). However vacuolation is not completely diagnostic since it may also be present to a lesser extent in the brains of healthy sheep <ref name="Fraser, 1976"> Fraser H, 1976. The pathology of a natural and experimental scrapie. Frontiers of Biology, 44:267-305.</ref>; <ref name="Zlotnik and Rennie, 1958"> Zlotnik I, Rennie JC, 1958. A comparative study of the incidence of vacuolated neurones in the medulla from apparently healthy sheep of various breeds. Journal of Comparative Pathology, 68:411-415.</ref>. In most instances the abnormal prion is resistant to protein kinase digestion, a feature used in diagnostic techniques.  
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+
  PrPSc 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 .
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Diagnosis is confirmed on '''post-mortem''' and PrP<sup>Sc</sup> can be isolated from brainstem or lymphoid tissues by Western immunoblot, immunohistochemistry (IHC) and [[ELISA testing|Elisa tests]]. Immunohistochemistry usually shows vacuolation and an accumulation of prion proteins in various parts of the CNS (medulla, pons, midbrain, and spinal cord). However vacuolation is not completely diagnostic since it may also be present to a lesser extent in the brains of healthy sheep <ref name="Fraser, 1976"> Fraser H (1976) '''The pathology of a natural and experimental scrapie. '''''Frontiers of Biology,'' 44:267-305.</ref>, <ref name="Zlotnik and Rennie, 1958"> Zlotnik I, Rennie JC (1958) '''A comparative study of the incidence of vacuolated neurones in the medulla from apparently healthy sheep of various breeds.''''' Journal of Comparative Pathology,'' 68:411-415.</ref>. In most instances the abnormal prion is resistant to protein kinase digestion, a feature used in diagnostic techniques. IHC staining of tonsil and lymphoid biopsies have been used for preclinical scrapie testing and the third eyelid lymphoid tissue can be used for diagnosis in sheep.  
+
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>
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'''Differential diagnoses''':  
 
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:Viral encephalomyelitides ([[Suid Herpesvirus 1|pseudorabies or Aujeszky’s disease]], [[rabies]], [[Visna-Maedi Virus|maedi visna]])
 
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:Bacterial meningoencephalomyelitides ([[listeriosis]])
 
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:[[Pregnancy Toxaemia|Pregnancy toxemia]] (ketosis)
 
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:Hypocalcemia-hypomagnesemia,  
 
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:Toxins (mercury, [[Lead Poisoning|lead]], organophosphates, plant toxins)  
 
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:Mange ([[Psoroptic Mange|psoroptic]], [[Sarcoptic Mange|sarcoptic]], [[Chorioptic Mange|chorioptic]]), [[:Category:Lice - Sheep|lice]], bacterial dermatitis <ref name="OIE, 2000">OIE (2000) '''Scrapie. OIE Manual of Standards for diagnostic tests and vaccines.''' 4 ed. ''Paris, France: Office International des Epizooties,'' 873-880.</ref>.
 
  
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‘’’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" />; <ref name="Radostits et al., 2000"> </ref>
 
==Treatment==
 
==Treatment==
 
Scrapie is a fatal condition and no effective treatment is currently available
 
Scrapie is a fatal condition and no effective treatment is currently available
−
 
 
==Control==
 
==Control==
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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.  
+
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>
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+
. 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>
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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">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>, <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. In 2001 the UK government set up the [http://animalhealth.defra.gov.uk/managing-disease/notifiable-disease/scrapie/national-scrapie-plan/ National Scrapie Plan NSP)] which aims to increase the frequency of the ARR allele within UK sheep population. Since 1988 it has been illegal for ruminant derived meat and bone meal to be fed to ruminants.
 
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{{Learning
 
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|flashcards = [[Scrapie in Sheep Flashcards]]
 
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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>.
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==References==
 
==References==
 
<references/>
 
<references/>
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{{CABI source
 
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|datasheet = [http://www.cabi.org/ahpc/?compid=3&dsid=64847&loadmodule=datasheet&page=2144&site=160 scrapie]
 
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[[Category:Neurological Diseases - Sheep]][[Category:Neurological Diseases - Cattle]]
 
[[Category:Transmissible Spongiform Encephalopathies]]
 
[[Category:Transmissible Spongiform Encephalopathies]]
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[[Category:CABI Expert Review]][[Category:CABI AHPC Pages]]
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[[Category:To_Do_-_Jaimie Meagor]]
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[[Category:To Do - Major]]

Revision as of 21:41, 7 June 2011

Also known as: TSE – Transmissible spongiform encephalopathy, Paraplexia enzootica ovium

Introduction

Scrapie was first described in the UK in 1732 [1], [2], and recognised as an infectious disease in 1936 [3], [4]. It is a progressive, fatal and non-febrile neurological disorder affecting sheep and goats. It belongs to a group of diseases called transmissible spongiform encephalopathy (TSE) and other TSE’s include Creutzfeldt-Jakob disease in humans, BSE, chronic wasting disease (CWD) in elk and deer, transmissible mink encephalopathy and feline spongiform encephalopathy has been found within cats in the UK. The disease is believed to be caused by a conformational change in the prion (PrP). A prion is a protein that occurs normally in the nervous and lymphoreticular tissues. It is only when the prion changes conformation into a protease-resistant protein PrPsc that it causes degeneration of neurological tissue. The disease causes astrocyte proliferation and then vacuolization of neurons but demyelination does not occur [5]. The abnormal protein is thought to act as a catalyst to convert more of the host’s protein into this abnormal form. The disease has been notifiable in the EU since 1993 but unlike BSE there is no evidence to suggest that scrapie is a risk to human health [6], [7],[8], [9]. Studies on the spread of scrapie infectivity have suggested that after oral intake, PrPSc first accumulates in Peyer’s patches of the small intestine, gut-associated lymphoid tissues (GALT) and ganglia of the enteric nervous system [10],[11], [12], [13], [14]. PrPSc then moves onward to the tonsil, spleen, retropharyngeal lymph nodes, mesenteric lymph nodes, and peripheral nervous tissue [15], [16],[17]. PrPSc eventually spreads to most lymph nodes and the central nervous system (CNS). PrPSc can be found in the lymphoreticular system tissues for months before it is found in the brain [18], [19], [20], [21]; [22]. Affected animals may live one to six months after onset of clinical signs [23], [24] , [25],[26], [27].

The original source of disease is thought to have come from imported Merino sheep from Spain [28], [29], and spread through the movement of of scrapie-infected preclinical sheep [30], [31], [32], [28], [33]. Scrapie is now endemic throughout Europe and most other continents [34], [35]. It has also been reported in goats [36], [37]; [38], [3], [39];[40], [41], [42], [43], [44], [45]. Only Australia and New Zealand are recognized as being currently free of scrapie.

Signalment

Scrapie has a long incubation period of two to five years [29] and affects the majority of sheep between 3 and 5 years of age. It is able to withstand a high degree of heat and high concentrations of formaldehyde [46]; [47] and unlike BSE is influenced by breed and genetic variations among sheep influence infectivity and the incubation period of scrapie. Research has shown that amino acid changes in at least three locations on the PrP gene (codons 136, 154, and 171), have been shown to confer increased or decreased susceptibility to scrapie [48]; [49]; [50]; [51]; Cite error: Closing </ref> missing for <ref> tag; [52], [53] , [54],; [55],, [56],, [57],, [58], [59],; [60],; [61],[62],[63],[64],[65], [66],. The disease has been shown to be effectively transmitted during lambing [67]; [41] as placenta and possibly the placental fluids are thought to be a source of infection [68]; [69]; [70]; [71]; [72] and experimental studies have shown that oral dosing of infected placenta can spread the disease in sheep and goats [73].

Clinical Signs

Early clinical signs may include subtle behavioural changes such as staring or fixed gaze, teeth grinding (bruxism), fine tremor, and hyperaesthesia to sound or sudden movements. Affected animals may later become intolerant to exercise and develop ataxia (awkwardness at turning, swaying of the hindquarters and some gait abnormalities such as a high stepping gait in the forelimbs or a bunny hopping gait in the hindlimbs). Some sheep have intense pruritis that leads to compulsive rubbing, nibbling at the skin, or scraping against fixed objects and may lead to wool loss (especially over the hindquarters and lateral thorax). A characteristic lip smacking or nibbling reflex can often be elicited by scratching over the lumbar region. In later stages there can be significant weight loss even without a noticeable decrease in appetite, weakness, recumbency, and death. [74], [75]; [76]; [77], [28]; [78]. It is important to note that some scrapie-infected sheep may appear healthy until stressed by transport, shearing, or pregnancy [34].

Diagnosis

A pre-emptive diagnosis of scrapie may be made from the above clinical signs combined with history and confirmed with laboratory tests. As there is no immune or inflammatory response there are no serological test available for scrapie [79]; [80] Pathologic lesions are confined to the CNS. Histology (immunohistochemistry) usually shows vacuolation and an accumulation of prion proteins in various parts of the CNS (medulla, pons, midbrain, and spinal cord). However vacuolation is not completely diagnostic since it may also be present to a lesser extent in the brains of healthy sheep [81]; [82]. In most instances the abnormal prion is resistant to protein kinase digestion, a feature used in diagnostic techniques. 

 PrPSc from post-mortem brainstem or lymphoid tissues may be detected by Western immunoblot analysis [83]; [84]; [85] and immunohistochemistry (IHC) [86] [87]; [88]; [89], [90] . Transmission to mice by injecting suspect tissue can be used to assay infectivity [35]tonsil [91]; [92] and lymphoid biopsies [93]; [94]; [95]; [88]; [96] stained for  PrPsc 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 PrPRes (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 PrPRes carried out following denaturation and concentration steps (Bio-Rad test)[97]

‘’’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 [35]; [78]

Treatment

Scrapie is a fatal condition and no effective treatment is currently available

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 [98] [99]; [97]; [100]. 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 [101] . Many countries use a combination of genetic selection, depopulation of infected sources and sourcing scrapie free flocks to control the spread of scrapie [100] and [102] 

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 [97]; [103].

References

  1. ↑ McGowan JP, 1922. Scrapie in sheep. Scottish Journal of Agriculture, 5:365-375.
  2. ↑ Pattison IH, 1988. Fifty years with scrapie: a personal reminiscence. Veterinary Record, 123(26-27):661-666; 60 ref.
  3. ↑ 3.0 3.1 Chelle PL, 1942. Un cas de tremblante chez la chèvre. Bulletin Académie Vétérinaire de France, 15:294-295.
  4. ↑ Poser CM, 2002. Notes on the history of the prion diseases. Part I. Clinical Neurology and Neurosurgery, 104(1):1-9.
  5. ↑ . Dandoy-Dron F, Guillo F, Benboudjema L, Deslys JP, Lasmézas C, Dormont D, Tovey MG, Dron M, 1998. Gene expression in scrapie. Cloning of a new scrapie-responsive gene and the identification of increased levels of seven other mRNA transcripts. Journal of Biological Chemistry, 273(13):7691-7697,48 ref.
  6. ↑ Brown P, Cathala F, Raubertas RF, Gajdusek DC, Castaigne P, 1987. The epidemiology of Creutzfeldt-Jakob disease: conclusion of a 15-year investigation in France and review of the world literature. Neurology, 37(6):895-904.
  7. ↑ Harries JR, Knight R, Will RG, Cousens SN, Smith PG, Mathews WB, 1988. Creutzfeldt-Jakob disease in England and Wales, 1980-1984: a case-control study of potential risk factors. Journal of Neurology Neurosurgery and Psychiatry, 51(9):1113-1119.
  8. ↑ Kondo K, Kuriowa Y, 1982. A case control study of Creutzfeldt-Jakob disease: association with physical injuries. Annals of Neurology, 11(4):377-381.
  9. ↑ World Health Organization, 1999. WHO consultation on public health and animal transmissible spongiform encephalopathies: epidemiology, risk and research requirements, with the participation of the Office International des Epizooties. http://www.who.int/csr/resources/publications/bse/WHO_CDS_CSR_APH_2000,Accessed 7 March 2005. http://www.who.int/csr/resources/publications/bse/en/whocdscsraph20002.pdf.
  10. ↑ Beekes M, McBride PA, 2000. Early accumulation of pathological PrP in the enteric nervous system and gut-associated lymphoid tissue of hamsters orally infected with scrapie. Neuroscience Letters, 278(3):181-184.
  11. ↑ Beekes M, McBride PA, Baldauf E, 1998. Cerebral targeting indicates vagal spread of infection in hamsters fed with scrapie. Journal of General Virology, 79(3):601-607; 20 ref.
  12. ↑ Heggebø R, Press CM, Gunnes G, Lie KaiInge, Tranulis MA, Ulvund M, Groschup MH, Landsverk T, 2000. Distribution of prion protein in the ileal Peyer's patch of scrapie-free lambs and lambs naturally and experimentally exposed to the scrapie agent. Journal of General Virology, 81(9):2327-2337; 2 pp. of ref.
  13. ↑ Kimberlin RH, Walker CA, 1989. Pathogenesis of scrapie in mice after intragastric infection. Virus Research, 12(3):213-220; 32 ref.
  14. ↑ Keulen LJMvan, Schreuder BEC, Vromans MEW, Langeveld JPM, Smits MA, 1999. Scrapie-associated prion protein in the gastro-intestinal tract of sheep with natural scrapie. Journal of Comparative Pathology, 121(1):55-63; 24 ref.
  15. ↑ Mabbott NA, Bruce ME, 2001. The immunobiology of TSE diseases. Journal of General Virology, 82(10):2307-2318; many ref.
  16. ↑ Maignien T, Lasmézas CI, Beringue V, Dormont D, Deslys JP, 1999. Pathogenesis of the oral route of infection of mice with scrapie and bovine spongiform encephalopathy agents. Journal of General Virology, 80(11):3035-3042; 32 ref.
  17. ↑ Press CM, Heggebø R, Espenes A, 2004. Involvement of gut-associated lymphoid tissue of ruminants in the spread of transmissible spongiform encephalopathies. Advanced Drug Delivery Reviews, 56(6):885-899.
  18. ↑ Eklund CM, Kennedy RC, Hadlow WJ, 1967. Pathogenesis of scrapie virus infection in the mouse. Journal of Infectious Diseases, 117(1):15-22.
  19. ↑ Hadlow W, Eklund CM, Kennedy RC, Jackson TA, Whitford HW, Boyle CC, 1974. Course of experimental scrapie virus infection in the goat. Journal of Infectious Diseases, 129(5):559-567.
  20. ↑ Hadlow W, Kennedy RC, Race RE, 1982. Natural infection of Suffolk sheep with scrapie virus. Journal of Infectious Diseases, 146(5):657-664.
  21. ↑ Hadlow WJ, Kennedy RC, Race RE, Eklund CM, 1980. Virologic and neurohistologic findings in dairy goats affected with natural scrapie. Veterinary Pathology, 17(2):187-199.
  22. ↑ Hadlow WJ, Race RE, Kennedy RC, Eklund CM, 1979. Natural infection of sheep with scrapie virus. Slow transmissible diseases of the nervous system. Volume 2., 3-12; 5 ref.
  23. ↑ Capucchio MT, Guarda F, Pozzato N, Coppolino S, Caracappa S, Marco Vdi, 2001. Clinical signs and diagnosis of scrapie in Italy: a comparative study in sheep and goats. Journal of Veterinary Medicine. Series A, 48(1):23-31; 11 ref.
  24. ↑ Foster J, Goldmann W, Parnham D, Chong A, Hunter N, 2001a. Partial dissociation of PrP deposition and vacuolation in the brains of scrapie and BSE experimentally affected goats. Journal of General Virology, 82(1):267-273; 30 ref.
  25. ↑ Foster JD et al., 2001b. Clinical signs, histopathology and genetics of experimental transmission of BSE and natural scrapie to sheep and goats. Vet. Rec., 148:165-171.
  26. ↑ Foster JD, Parnham D, Chong A, Goldmann W, Hunter N, 2001c. Clinical signs, histopathology and genetics of experimental transmission of BSE and natural scrapie to sheep and goats. Veterinary Record, 148(6):165-171, 22 .
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  102. ↑ 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.
  103. ↑ 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.



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