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| + | Scrapie is a neurological disease of sheep first recorded in 1732. Clinical signs include progressive ataxia and pruritis. Histology shows vacuolation of CNS (brain and spinal cord). Agent of disease is a prion, which is a transmissible, infectious protein with an abnormal folding structure. |
| − | Also known as: '''''Transmissible Spongiform Encephalopathy of Sheep — TSE — Paraplexia enzootica ovium'''''
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| − | ==Introduction==
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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 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.
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| − | ==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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| − | 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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| − | [[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.
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| − | ==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 and history. There are no serological test available for scrapie, as is does not evoke an immune or inflammatory response.
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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.
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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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| − | ==Treatment==
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| − | Scrapie is a fatal condition and no effective treatment is currently available
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| − | ==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.
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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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| − | ==References==
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| − | <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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| − | |date =5 April 2011
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| − | <br><br><br>
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| − | {{review}}
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| − | {{OpenPages}}
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| − | [[Category:Neurological Diseases - Sheep]][[Category:Neurological Diseases - Goat]]
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| − | [[Category:Transmissible Spongiform Encephalopathies]]
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| − | [[Category:CABI Expert Review]][[Category:CABI AHPC Pages]]
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