Invasive Species Compendium

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scrapie

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scrapie

Summary

  • Last modified
  • 25 November 2019
  • Datasheet Type(s)
  • Animal Disease
  • Preferred Scientific Name
  • scrapie
  • Overview
  • Note: This datasheet covers 'classical' scrapie, not 'atypical' scrapie.

    Scrapie is a fatal neurodegenerative disease of sheep and goats. It is part of a group of diseases classified as transmissible spongiform encephalopathies (TSEs). T...

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    Compendia
    CAB International
    Wallingford
    Oxfordshire
    OX10 8DE
    UK
    compend@cabi.org
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Identity

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Preferred Scientific Name

  • scrapie

International Common Names

  • English: Paraplexia enzootica ovium; scrapie in goats; scrapie in sheep; spongiform encephalopathies; spongiform encephalopathy, scrapie; transmissible spongiform encephalopathies
  • French: la tremblante; tremblante du mouton

Local Common Names

  • Germany: Traberkrankheit
  • Norway: Rida

English acronym

  • TSE

Overview

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Note: This datasheet covers 'classical' scrapie, not 'atypical' scrapie.

Scrapie is a fatal neurodegenerative disease of sheep and goats. It is part of a group of diseases classified as transmissible spongiform encephalopathies (TSEs). These diseases include bovine spongiform encephalopathy (BSE) in cattle, chronic wasting disease (CWD) in elk and deer, transmissible mink encephalopathy, and Creutzfeldt-Jakob disease (vCJD) in humans. The infectious agent is thought to be a prion, an agent smaller than the smallest known virus. Scrapie has a long history with the first descriptions dating back over 250 years. Despite this long history, many factors of the disease are still not fully understood, including a complete characterization of the infectious agent, routes of transmission and pathogenesis. Recent evidence linking vCJD in humans to BSE in cattle has increased attention for all TSEs, including scrapie. There are many laboratories in several different countries actively conducting research on scrapie and other TSEs. There is no evidence to date that scrapie is a risk to human health (Brown et al., 1987; Harries et al., 1988; Kondo and Kuriowa, 1982; WHO, 1999).

Scrapie was first described in the UK in 1732 (McGowan, 1922; Pattison, 1988) and recognized as an infectious disease in 1936 (Chelle, 1942; Poser, 2002). The extremely long incubation period of two to five years was noted as long ago as 1913 (Stockman, 1913). Pattison was the first to show transmission of scrapie to another species, a goat, in 1957 (Pattison, 1957; Pattison and Millson, 1961). In 1961 Chandler showed transmission to mice (Chandler, 1961). Pattison in 1965 showed that the scrapie agent was able to withstand a high degree of heat and high concentrations of formaldehyde (Pattison, 1965; Stamp et al., 1959). In 1966 Alper and colleagues first suggested that the scrapie agent was able to replicate despite apparently lacking nucleic acid (Alper et al., 1966). Prusiner in 1982 proposed that the scrapie agent was a nucleic acid-free proteinaceous infectious molecule or prion (Prusiner, 1982). Later work by Prusiner and colleagues showed that the prion protein (PrP) was a component of the normal cell and was encoded by the host genome (Oesch et al., 1985). The incubation time of scrapie was thought to be controlled by a single gene, Sip (scrapie incubation period) (Dickinson and Outram, 1988). The gene encoding PrP was subsequently found to be congruent to Sip in sheep (Moore et al., 1998). Prion protein is a normal cellular protein in many mammalian cell types (Prusiner, 1998). The normal cellular form undergoes a conformational change to a protease-resistant protein (PrPSc). The abnormal protein form of the host cellular protein is thought to act as a catalyst to convert more of the host’s protein to the abnormal form. Prusiner was awarded the 1997 Nobel Prize in Physiology or Medicine for his work on the infectious nature of prions. Soto and colleagues provided strong evidence that PrPSc is the infective agent of scrapie in a series of experiments reporting reversal of infectivity in PrPSc (Soto et al., 2000).

While scrapie has a long history and attempts have been made over the years to control and eradicate the disease, it remains endemic in many countries.

Scrapie has been recognized as a disease of sheep for more than 250 years. It is one of a small number of diseases known as the transmissible spongiform encephalopathies, along with:

 


Disease Species affected
   
1. scrapie sheep, goats, mouflon
2. bovine spongiform encephalopathy (BSE) cattle, antelopes, bison
3. feline spongiform encephalopathy cats, puma, cheetah, ocelots
4. transmissible mink encephalopathy farmed mink
5. chronic wasting syndromeCervus elaphus, mule deer
6. kuru humans
7. Gerstmann-Straussler syndrome humans
8. Creutzfeldt-Jacob disease (CJD) humans
9. variant CJD humans

 

Host Animals

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Animal nameContextLife stageSystem
Capra hircus (goats)Domesticated hostSheep and Goats|All Stages
Cricetus cricetusExperimental settings
Mus musculus (house mouse)Experimental settings
Ovis aries (sheep)Domesticated hostSheep and Goats|All Stages

Hosts/Species Affected

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Genetic variations among sheep influence infectivity and the incubation period of scrapie. 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 (Belt et al., 1995; Billinis et al., 2004; Clouscard et al., 1995; Elsen et al., 1999; Goldmann et al., 1991; Goldmann et al., 1990; Goldmann et al., 1994a,b; Hunter and Cairns, 1998; Hunter et al., 1997a,b,c; Hunter et al., 1991; Hunter et al., 1996; Hunter et al., 1992; Hunter et al., 1993Hunter et al., 1994Ikeda et al., 1995; Thorgeirsdottir et al., 1999; Tranulis et al., 1999; Westaway et al., 1994). The incidence of scrapie in various breeds of sheep has been associated with some of those polymorphisms (Bossers et al., 1996; Dickinson et al., 1968; Goldmann et al., 1991; Goldmann et al., 1990; Goldmann et al., 1994a; Hunter et al., 1991; Hunter et al., 1996; Hunter et al., 1992; Hunter et al., 1993; Hunter et al., 1997a,b; Hunter et al., 1994Laplanche et al., 1993a; O'Rourke et al., 1997). At codon 136, the amino acid valine (V) has been linked to scrapie susceptibility while an alanine (A) was linked to resistance (Hunter et al., 1996; Hunter et al., 1994). At codon 171, glutamine (Q) or histidine (H) have been linked to scrapie susceptibility while an arginine (R) has been linked to resistance (Hunter, 1997; Ikeda et al., 1995; O'Rourke et al., 1996; Westaway et al., 1994). At codon 154, histidine (H) was linked to susceptibility while arginine (R) was linked to resistance (Laplanche et al., 1993a). Variation at codon 154 was shown to modulate incubation time in some breeds and may decrease susceptibility in other breeds (Dawson et al., 1998; Thorgeirsdottir et al., 1999). With very few exceptions, naturally infected sheep of a number of breeds in the USA, UK, Europe and Japan carry either 136 Valine (136 Valine/Valine or 136 Valine/Alanine) or 171 Glutamine/Glutamine (QQ) (Belt et al., 1995; Clouscard et al., 1995; Hunter et al., 1993; Hunter et al., 1994; Ikeda et al., 1995; Laplanche et al., 1993; Laplanche et al., 1993; O'Rourke et al., 1996; Westaway et al., 1994). There has been only one report of a scrapie-affected Suffolk carrying 171 Arginine/Arginine (RR) (Ikeda et al., 1995) and four published reports of scrapie-affected Suffolks with 171 Glutamine/Arginine (QR) (Hunter et al., 1997c; Ikeda et al., 1995).

PrP genotyping can be used as an aid in the control of scrapie. Several researchers have proposed breeding stock of resistant PrP genotypes and selection to produce progeny with reduced risk of disease (Dawson et al., 1998; Drögemüeller et al., 2001; Parry, 1979; Schreuder et al., 1997). The genotype of the fetus was found to be a factor in the deposition of PrPSc in the placenta (Andréoletti et al., 2002; Tuo et al., 2002). The fetal ARR allele was found to be associated with a lack of PrPSc deposition. Fetuses homozygous for ARQ were also shown to lack PrPSc in the placenta.

There are research efforts currently underway in several countries examining the possibility of a carrier state for scrapie; animals that become infected and shed the scrapie agent, but do not progress to develop clinical disease. Studies thus far have failed to detect such animals (Elsen et al., 1999), USDA-ARS, Pullman, WA, unpublished results.

Polymorphisms of the gene encoding the PrP protein have been found at many codons in the goat (Billinis et al., 2002; Goldmann et al., 1996), but only a couple have been associated with scrapie to date (Billinis et al., 2002; Goldmann et al., 1998; Goldmann et al., 1996). Research is continuing in this area and should provide more insight as more scrapie cases in goats are detected.

Other risk factors include sanitation issues such as not disposing of placental tissues and contaminated bedding after lambing. Farms that employed breeding and lambing management practices with lambing occurring in group pens were found more likely to report scrapie than farms where lambing occurred on pasture or in individual pens (Elsen et al., 1999; McLean et al., 1999).

Systems Affected

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blood and circulatory system diseases of small ruminants
digestive diseases of small ruminants
nervous system diseases of small ruminants
reproductive diseases of small ruminants
skin and ocular diseases of small ruminants

Distribution

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The spread of sheep scrapie in Europe has been reported to have resulted from the importation of certain breeds of sheep such as the Merino from Spain (Parry and Oppenheimer, 1983; Stockman, 1913). The disease was spread through the movement of scrapie-infected preclinical sheep (Brash, 1952; Bull and Murnane, 1958; Cooper, 1973; Parry and Oppenheimer, 1983; Merwe, 1966). Scrapie was imported into Canada from the UK in 1938 (Schofield, 1938). The first case of scrapie in the USA was diagnosed in 1947 in a Michigan flock (USDA, 2005). The flock owner had imported sheep of British origin through Canada for several years. The incidence within a flock can be variable with reports in UK ranging from 0.37% to 20% (Hoinville et al., 2000; Hoinville et al., 1999; Schreuder et al., 1993; Sigurdarson, 1991).

Scrapie is endemic in many European countries and has been reported in several countries throughout most other continents (Detwiler and Baylis, 2003; OIE, 2000). Scrapie in goats has been reported in many countries (Andrews et al., 1992; Brotherston et al., 1968; Capucchio et al., 1998; Chelle, 1942; Fankhauser et al., 1982; Harcourt, 1974; Hourrigan et al., 1979; Leontides et al., 2000; Stemshorn, 1975; Toumazos, 1991; Toumazos and Alley, 1989). Only Australia and New Zealand are recognized as being free of scrapie.

Scrapie has been a notifiable disease within the EU since 1993, and many countries of the EU as well as the USA and Canada use active surveillance programs where slaughter surveillance combined with mandatory identification provides information on national and regional prevalence(CFIA, 2005; European Commission, 2001; USDA, 2005). Many countries lack a surveillance program, so their scrapie status is unknown. There is no preclinical screening test that reliably detects all scrapie-infected sheep so determining the scrapie status of countries is difficult. Passive surveillance, or data collected from disease observations on an ad hoc basis, is not adequate for detecting all cases of scrapie. Australia and New Zealand appear to have successfully eliminated scrapie after the introduction of the disease from imported sheep by the complete depopulation of all imports and all contact sheep (Detwiler and Baylis, 2003).

For current information on disease incidence, see OIE's WAHID Interface.

Distribution Table

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The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.

Last updated: 07 Jan 2022
Continent/Country/Region Distribution Last Reported Origin First Reported Invasive Reference Notes

Africa

AlgeriaAbsentJul-Dec-2019
AngolaAbsent, No presence record(s)Jul-Dec-2018
BeninAbsent, No presence record(s)
BotswanaAbsentJul-Dec-2018
BurundiAbsentJul-Dec-2018
Cabo VerdeAbsent, No presence record(s)Jul-Dec-2019
CameroonAbsent, No presence record(s)
Central African RepublicAbsent, No presence record(s)Jul-Dec-2019
ChadAbsentJul-Dec-2019
ComorosAbsent, No presence record(s)Jan-Jun-2018
Congo, Democratic Republic of theAbsent, No presence record(s)
Côte d'IvoirePresent, LocalizedJul-Dec-2019
DjiboutiAbsent, No presence record(s)Jul-Dec-2019
EgyptAbsent, No presence record(s)Jul-Dec-2019
EritreaAbsentJul-Dec-2019
EswatiniAbsent, No presence record(s)Jul-Dec-2019
EthiopiaAbsent, No presence record(s)Jul-Dec-2018
GhanaAbsentJan-Jun-2019
GuineaAbsent, No presence record(s)Jan-Jun-2019
KenyaAbsent, No presence record(s)Jul-Dec-2019
LesothoAbsent, No presence record(s)Jan-Jun-2020
LibyaAbsentJul-Dec-2019
MadagascarAbsent, No presence record(s)Jan-Jun-2019
MalawiAbsent, No presence record(s)Jul-Dec-2018
MauritiusAbsent, No presence record(s)Jul-Dec-2019
MayotteAbsent, No presence record(s)Jul-Dec-2019
MoroccoAbsent, No presence record(s)Jul-Dec-2019
MozambiqueAbsentJul-Dec-2019
NamibiaAbsentJul-Dec-2019
NigerAbsentJul-Dec-2019
NigeriaAbsent, No presence record(s)Jul-Dec-2019
RéunionAbsent, No presence record(s)Jul-Dec-2019
RwandaAbsentJan-Jun-2018
Saint HelenaAbsent, No presence record(s)Jan-Jun-2019
SeychellesAbsent, No presence record(s)Jul-Dec-2018
Sierra LeoneAbsentJan-Jun-2018
SomaliaAbsentJul-Dec-2020
South AfricaAbsentJul-Dec-2019
SudanAbsent, No presence record(s)Jul-Dec-2019
TogoAbsent, No presence record(s)Jul-Dec-2019
TunisiaPresentJul-Dec-2020
ZambiaAbsent, No presence record(s)Jul-Dec-2018
ZimbabweAbsent, No presence record(s)Jul-Dec-2019

Asia

AfghanistanAbsent, No presence record(s)Jul-Dec-2019
ArmeniaAbsentJul-Dec-2019
AzerbaijanAbsentJul-Dec-2019
BahrainAbsent, No presence record(s)Jul-Dec-2020
BangladeshAbsent, No presence record(s)Jan-Jun-2020
BhutanAbsent, No presence record(s)Jan-Jun-2020
BruneiAbsent, No presence record(s)Jul-Dec-2019
ChinaAbsent, No presence record(s)Jul-Dec-2018
GeorgiaAbsent, No presence record(s)Jul-Dec-2019
Hong KongAbsent, No presence record(s)Jul-Dec-2019
IndiaAbsent, No presence record(s)Jan-Jun-2019
IndonesiaAbsent, No presence record(s)Jul-Dec-2019
IranAbsent, No presence record(s)Jan-Jun-2019
IraqAbsentJul-Dec-2019
IsraelPresentJul-Dec-2020
JapanAbsentJan-Jun-2020
JordanAbsent, No presence record(s)Jul-Dec-2018
KazakhstanAbsent, No presence record(s)Jul-Dec-2019
KuwaitAbsent, No presence record(s)Jan-Jun-2019
KyrgyzstanAbsent, No presence record(s)Jan-Jun-2019
LaosAbsent, No presence record(s)Jan-Jun-2019
LebanonAbsent, No presence record(s)Jul-Dec-2019
MalaysiaAbsent, No presence record(s)Jan-Jun-2019
-SabahAbsent, No presence record(s)
-SarawakAbsent, No presence record(s)
MaldivesAbsent, No presence record(s)Jan-Jun-2019
MongoliaAbsent, No presence record(s)Jan-Jun-2019
MyanmarAbsent, No presence record(s)Jul-Dec-2019
NepalAbsent, No presence record(s)Jul-Dec-2019
North KoreaAbsent, No presence record(s)
OmanAbsentJul-Dec-2019
PakistanAbsent, No presence record(s)Jan-Jun-2020
PalestineAbsentJul-Dec-2019
PhilippinesAbsent, No presence record(s)Jul-Dec-2019
QatarAbsentJul-Dec-2019
Saudi ArabiaAbsent, No presence record(s)Jan-Jun-2020
SingaporeAbsent, No presence record(s)Jul-Dec-2019
South KoreaAbsentJul-Dec-2019
Sri LankaAbsent, No presence record(s)Jul-Dec-2018
SyriaAbsentJul-Dec-2019
TaiwanAbsent, No presence record(s)Jul-Dec-2019
TajikistanAbsentJan-Jun-2019
ThailandAbsent, No presence record(s)
TurkmenistanAbsentJan-Jun-2019
United Arab EmiratesAbsent, No presence record(s)Jul-Dec-2020
UzbekistanAbsent, No presence record(s)Jul-Dec-2019
VietnamAbsent, No presence record(s)Jul-Dec-2019

Europe

AndorraAbsent, No presence record(s)Jul-Dec-2019
AustriaAbsentJul-Dec-2019
BelarusAbsentJul-Dec-2019
BelgiumAbsentJul-Dec-2019
Bosnia and HerzegovinaAbsent, No presence record(s)Jul-Dec-2019
BulgariaAbsentJan-Jun-2019
CroatiaAbsent, No presence record(s)Jul-Dec-2019
CyprusPresentJul-Dec-2019
CzechiaAbsentJul-Dec-2019
DenmarkAbsent, No presence record(s)Jan-Jun-2019
EstoniaAbsent, No presence record(s)Jul-Dec-2019
Faroe IslandsPresentJul-Dec-2018
FinlandAbsentJul-Dec-2019
FrancePresent, LocalizedJul-Dec-2019
GermanyPresentJul-Dec-2019
GreecePresentJan-Jun-2018
HungaryAbsentJul-Dec-2019
IcelandPresentJul-Dec-2020
IrelandPresentJul-Dec-2019
ItalyPresent, LocalizedJul-Dec-2020
JerseyAbsent, No presence record(s)
LatviaAbsent, No presence record(s)Jul-Dec-2020
LiechtensteinAbsentJul-Dec-2019
LithuaniaAbsent, No presence record(s)Jul-Dec-2019
LuxembourgAbsent, No presence record(s)
MaltaAbsent, No presence record(s)Jan-Jun-2019
MoldovaAbsent, No presence record(s)Jan-Jun-2020
MontenegroAbsentJan-Jun-2018
NetherlandsAbsentJul-Dec-2019
North MacedoniaAbsent, No presence record(s)Jul-Dec-2019
NorwayPresent, LocalizedJul-Dec-2019
PolandAbsent, No presence record(s)Jan-Jun-2019
PortugalPresentJan-Jun-2020
RomaniaPresent, LocalizedJul-Dec-2018
RussiaAbsentJan-Jun-2020
San MarinoAbsent, No presence record(s)Jan-Jun-2019
SerbiaAbsentJul-Dec-2019
Serbia and MontenegroAbsent, No presence record(s)
SlovakiaPresentJul-Dec-2020
SloveniaAbsentJul-Dec-2018
SpainPresent, LocalizedJul-Dec-2020
SwedenAbsentJul-Dec-2020
SwitzerlandAbsentJul-Dec-2020
UkraineAbsent, No presence record(s)Jul-Dec-2020
United KingdomPresentJul-Dec-2019
-Northern IrelandPresent

North America

BahamasAbsent, No presence record(s)Jul-Dec-2018
BarbadosAbsent, No presence record(s)Jul-Dec-2020
BelizeAbsent, No presence record(s)Jul-Dec-2019
BermudaAbsent, No presence record(s)
British Virgin IslandsAbsent, No presence record(s)
CanadaPresentJul-Dec-2019
Cayman IslandsAbsent, No presence record(s)Jan-Jun-2019
Costa RicaAbsent, No presence record(s)Jul-Dec-2019
CubaAbsent, No presence record(s)Jan-Jun-2019
CuraçaoAbsent, No presence record(s)Jan-Jun-2019
DominicaAbsent, No presence record(s)
Dominican RepublicAbsent, No presence record(s)Jan-Jun-2019
El SalvadorAbsent, No presence record(s)Jul-Dec-2019
GreenlandAbsent, No presence record(s)Jul-Dec-2018
GuadeloupeAbsent, No presence record(s)Jul-Dec-2019
GuatemalaAbsent, No presence record(s)Jan-Jun-2019
HaitiAbsent, No presence record(s)Jul-Dec-2019
HondurasAbsent, No presence record(s)Jul-Dec-2018
JamaicaAbsent, No presence record(s)Jul-Dec-2018
MartiniqueAbsentJul-Dec-2019
MexicoAbsent, No presence record(s)Jul-Dec-2019
NicaraguaAbsent, No presence record(s)Jul-Dec-2019
PanamaAbsent, No presence record(s)Jan-Jun-2019
Saint Kitts and NevisAbsent, No presence record(s)
Saint LuciaAbsent, No presence record(s)Jul-Dec-2018
Saint Vincent and the GrenadinesAbsent, No presence record(s)Jan-Jun-2019
Trinidad and TobagoAbsent, No presence record(s)Jan-Jun-2018
United StatesPresentJul-Dec-2019

Oceania

AustraliaAbsentJul-Dec-2019
Cook IslandsAbsent, No presence record(s)Jan-Jun-2019
Federated States of MicronesiaAbsent, No presence record(s)Jan-Jun-2019
FijiAbsent, No presence record(s)Jan-Jun-2019
French PolynesiaAbsent, No presence record(s)Jan-Jun-2019
KiribatiAbsent, No presence record(s)Jan-Jun-2018
Marshall IslandsAbsent, No presence record(s)Jan-Jun-2019
New CaledoniaAbsent, No presence record(s)Jul-Dec-2019
New ZealandAbsentJul-Dec-2019
PalauAbsent, No presence record(s)Jul-Dec-2020
SamoaAbsent, No presence record(s)Jan-Jun-2019
Timor-LestePresentJul-Dec-2018
TongaAbsentJul-Dec-2019
VanuatuAbsent, No presence record(s)Jan-Jun-2019

South America

ArgentinaAbsent, No presence record(s)Jul-Dec-2019
BoliviaAbsent, No presence record(s)Jan-Jun-2019
BrazilPresentJul-Dec-2019
ChileAbsent, No presence record(s)Jan-Jun-2019
ColombiaAbsent, No presence record(s)Jul-Dec-2019
EcuadorAbsent, No presence record(s)Jul-Dec-2019
Falkland IslandsAbsent, No presence record(s)Jul-Dec-2019
French GuianaAbsentJul-Dec-2019
GuyanaAbsent, No presence record(s)Jul-Dec-2018
ParaguayAbsent, No presence record(s)Jul-Dec-2019
PeruAbsent, No presence record(s)Jan-Jun-2019
SurinameAbsent, No presence record(s)Jan-Jun-2019
UruguayAbsent, No presence record(s)Jul-Dec-2019
VenezuelaAbsent, No presence record(s)Jan-Jun-2019

Pathology

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Pathologic lesions are restricted to microscopic changes in the CNS. Grossly, sheep and goats may show a loss of body condition and there may be wool loss in sheep that are pruritic and scraping.

Diagnosis

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Clinical diagnosis


A preemptive diagnosis of scrapie may be made from clinical signs combined with history. Diagnosis cannot be confirmed without laboratory tests.


Lesions


Microscopic changes in the CNS are degenerative and unaccompanied by inflammation. Single or multiple vacuoles surrounded by a zone of cytoplasmic degeneration may be present in the neurons of the medulla, pons, midbrain, and spinal cord. The surrounding neuropil may also be affected by spongiform changes (Brown et al., 1999; Fraser, 1976; Wells and McGill, 1992; Wood et al., 1997). The vacuolation is not completely diagnostic since it may also be present to a lesser extent in the brains of healthy sheep (Fraser, 1976; Zlotnik and Rennie, 1958). Astrocyte proliferation precedes the vacuolization of neurons and demyelination does not occur (Dandoy-Dron et al., 1998).


Differential diagnosis


Scrapie may be confused with other neurological diseases or other diseases that cause progressive loss of condition or pruritus with skin lesions. Major differentials (OIE, 2000; Radostits et al., 2000) include:

Viral encephalomyelitides (pseudorabies or Aujeszky’s disease, rabies, maedi visna)
Bacterial meningoencephalomyelitides (listeriosis)
Pregnancy toxemia (ketosis)
Hypocalcemis-hypomagnesemia
Toxins (mercury, lead, organophosphates, plant toxins)
Mange, lice, bacterial dermatitis


Laboratory diagnosis


There are no serological tests available for scrapie. No immune response or inflammatory response has been detected (Kasper et al., 1982; Porter et al., 1973). PrPSc from postmortem brainstem or lymphoid tissues may be detected by Western immunoblot analysis (Farquhar et al., 1989; Stack et al., 1996; Wadsworth et al., 2001) and immunohistochemistry (IHC) (Miller et al., 1993; Miller et al., 1994; O'Rourke et al., 1998Keulen et al., 1996Keulen et al., 1995). Transmission to mice by injecting suspect tissue can be used to assay infectivity (OIE, 2000).


Other diagnostic tests


Tonsil biopsies with subsequent staining for PrPSc by IHC can be used for preclinical scrapie screening (Schreuder et al., 1998; Schreuder et al., 1996). In the most susceptible genotypes, PrPSc was found in the tonsils of sheep at four to five months of age (Schreuder et al., 1998). Preclinical antemortem testing is also available detecting PrPSc by IHC in nictitating membrane lymphoid biopsies (Bender et al., 2004; Ikegami et al., 1991; O'Rourke et al., 2000; O'Rourke et al., 1998; Thuring et al., 2000). The third eyelid lymphoid tissue can be used for diagnosis in sheep over 14 months of age and was recognized in 2001 as an official preclinical screening test for scrapie in the USA. Biopsy of the rectoanal-associated lymphoid tissue and with PrPSc by IHC can also be used to identify pre-clinical infection (Gonzalez et al., 2005).

Rapid immuno- or ligand binding assays that are currently approved by the EU for active surveillance for small ruminant TSEs (European Commission, 2001) are:

Bio-Rad TeSeE rapid test

Bio-Rad TeSeE Sheep/Goat rapid test

Enfer TSE Kit version 2.0

Enfer TSE Version 3

IDEXX HerdChek BSE-Scrapie Antigen Test Kit, EIA

Prionics-Check Western Small Ruminant test

Prionics Check LIA Small Ruminants

(Commission Regulation (EC) No 162/2009) 

Also approved by the EFSA BIOHAZ Panel and awaiting statutory incorporation to the EU approved list is the Prionics Check Prio STRIP SR (EFSA Panel on Biological Hazards, 2012).

At this time only IHC of brain or lymphoid tissues has been approved for diagnosis of scrapie in the USA.

List of Symptoms/Signs

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SignLife StagesType
Acoustic Signs / Rubbing ears, scratching Sheep and Goats|Breeding male; Sheep and Goats|Gimmer; Sheep and Goats|Hogget; Sheep and Goats|Mature female Sign
Cardiovascular Signs / Arrhythmia, irregular heart rate, pulse Sign
Digestive Signs / Abdominal distention Sign
Digestive Signs / Anorexia, loss or decreased appetite, not nursing, off feed Sign
Digestive Signs / Anorexia, loss or decreased appetite, not nursing, off feed Sign
Digestive Signs / Bloat in ruminants, tympany Sign
Digestive Signs / Decreased amount of stools, absent faeces, constipation Sign
Digestive Signs / Difficulty in prehending or chewing food Sign
Digestive Signs / Excessive salivation, frothing at the mouth, ptyalism Sign
Digestive Signs / Grinding teeth, bruxism, odontoprisis Sign
Digestive Signs / Grinding teeth, bruxism, odontoprisis Sign
Digestive Signs / Rumen hypomotility or atony, decreased rate, motility, strength Sign
Digestive Signs / Vomiting or regurgitation, emesis Sign
Digestive Signs / Vomiting or regurgitation, emesis Sign
General Signs / Abnormal proprioceptive positioning, knuckling Sign
General Signs / Abnormal proprioceptive positioning, knuckling Sign
General Signs / Ataxia, incoordination, staggering, falling Sign
General Signs / Ataxia, incoordination, staggering, falling Sign
General Signs / Bunny hopping Sign
General Signs / Bunny hopping Sign
General Signs / Dysmetria, hypermetria, hypometria Sign
General Signs / Dysmetria, hypermetria, hypometria Sign
General Signs / Exercise intolerance, tires easily Sign
General Signs / Exercise intolerance, tires easily Sign
General Signs / Forelimb weakness, paresis, paralysis front leg Sign
General Signs / Generalized weakness, paresis, paralysis Sign
General Signs / Generalized weakness, paresis, paralysis Sign
General Signs / Head, face, ears, jaw weakness, droop, paresis, paralysis Sheep and Goats|Breeding male; Sheep and Goats|Gimmer; Sheep and Goats|Hogget; Sheep and Goats|Mature female Sign
General Signs / Inability to stand, downer, prostration Sign
General Signs / Inability to stand, downer, prostration Sign
General Signs / Kyphosis, arched back Sign
General Signs / Paraparesis, weakness, paralysis both hind limbs Sign
General Signs / Paraparesis, weakness, paralysis both hind limbs Sign
General Signs / Sudden death, found dead Sheep and Goats|Breeding male; Sheep and Goats|Gimmer; Sheep and Goats|Hogget; Sheep and Goats|Mature female Sign
General Signs / Tetraparesis, weakness, paralysis all four limbs Sign
General Signs / Tetraparesis, weakness, paralysis all four limbs Sign
General Signs / Trembling, shivering, fasciculations, chilling Sign
General Signs / Trembling, shivering, fasciculations, chilling Sign
General Signs / Underweight, poor condition, thin, emaciated, unthriftiness, ill thrift Sign
General Signs / Underweight, poor condition, thin, emaciated, unthriftiness, ill thrift Sign
General Signs / Weakness of one hindlimb, paresis paralysis rear leg Sheep and Goats|Breeding male; Sheep and Goats|Gimmer; Sheep and Goats|Hogget; Sheep and Goats|Mature female Sign
General Signs / Weight loss Sign
General Signs / Weight loss Sign
Musculoskeletal Signs / Forelimb spasms, myoclonus Sign
Musculoskeletal Signs / Hindlimb spasms, myoclonus Sign
Nervous Signs / Abnormal behavior, aggression, changing habits Sign
Nervous Signs / Abnormal behavior, aggression, changing habits Sign
Nervous Signs / Abnormal forelimb reflexes, increased or decreased Sign
Nervous Signs / Abnormal hindlimb reflexes, increased or decreased Sign
Nervous Signs / Circling Sign
Nervous Signs / Coma, stupor Sheep and Goats|Breeding male; Sheep and Goats|Gimmer; Sheep and Goats|Hogget; Sheep and Goats|Mature female Sign
Nervous Signs / Disoriented, memory loss Sign
Nervous Signs / Dullness, depression, lethargy, depressed, lethargic, listless Sign
Nervous Signs / Dullness, depression, lethargy, depressed, lethargic, listless Sign
Nervous Signs / Excitement, delirium, mania Sign
Nervous Signs / Excitement, delirium, mania Sign
Nervous Signs / Forelimb hypoesthesia, anesthesia front leg Sign
Nervous Signs / Head pressing Sign
Nervous Signs / Head shaking, headshaking Sheep and Goats|Breeding male; Sheep and Goats|Gimmer; Sheep and Goats|Hogget; Sheep and Goats|Lamb; Sheep and Goats|Mature female Sign
Nervous Signs / Head tilt Sheep and Goats|Breeding male; Sheep and Goats|Gimmer; Sheep and Goats|Hogget; Sheep and Goats|Lamb; Sheep and Goats|Mature female Sign
Nervous Signs / Hindlimb hypoesthesia, anesthesia rear leg Sign
Nervous Signs / Hyperesthesia, irritable, hyperactive Sign
Nervous Signs / Hyperesthesia, irritable, hyperactive Sign
Nervous Signs / Muscle hypotonia Sign
Nervous Signs / Propulsion, aimless wandering Sheep and Goats|Breeding male; Sheep and Goats|Gimmer; Sheep and Goats|Hogget; Sheep and Goats|Lamb; Sheep and Goats|Mature female Sign
Nervous Signs / Seizures or syncope, convulsions, fits, collapse Sign
Nervous Signs / Seizures or syncope, convulsions, fits, collapse Sign
Nervous Signs / Tremor Sign
Nervous Signs / Tremor Sign
Ophthalmology Signs / Blindness Sign
Ophthalmology Signs / Blindness Sign
Ophthalmology Signs / Decreased or absent menace response but not blind Sheep and Goats|Breeding male; Sheep and Goats|Gimmer; Sheep and Goats|Hogget; Sheep and Goats|Mature female Sign
Ophthalmology Signs / Nystagmus Sign
Ophthalmology Signs / Retinal folds or elevations Sign
Ophthalmology Signs / Retinal folds or elevations Sign
Reproductive Signs / Abortion or weak newborns, stillbirth Sign
Reproductive Signs / Agalactia, decreased, absent milk production Sign
Respiratory Signs / Change in voice, vocal strength Sign
Respiratory Signs / Change in voice, vocal strength Sign
Respiratory Signs / Coughing, coughs Sign
Skin / Integumentary Signs / Alopecia, thinning, shedding, easily epilated, loss of, hair Sign
Skin / Integumentary Signs / Alopecia, thinning, shedding, easily epilated, loss of, hair Sign
Skin / Integumentary Signs / Hyperkeratosis, thick skin Sign
Skin / Integumentary Signs / Pruritus, itching skin Sign
Skin / Integumentary Signs / Pruritus, itching skin Sign
Skin / Integumentary Signs / Skin crusts, scabs Sign
Skin / Integumentary Signs / Skin erythema, inflammation, redness Sign
Skin / Integumentary Signs / Skin ulcer, erosion, excoriation Sign

Disease Course

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The majority of cases of scrapie in sheep occur in animals between three to five years of age. It is generally thought that transmission is most efficient during lambing (Dickinson et al., 1974; Hourrigan et al., 1979). Horizontal transmission of scrapie has been shown in field conditions with unrelated sheep (Brotherston et al., 1968; Dickinson et al., 1974; Hourrigan et al., 1979) and in heavily infected flocks (Matthews et al., 1999; Ryder et al., 2004; Woolhouse et al., 1998). Horizontal transmission to goats reared with infected sheep has also been documented (Billinis et al., 2002; Brotherston et al., 1968; Dickinson et al., 1974; Toumazos and Alley, 1989). The placenta and possibly the placental fluids are thought to be a source of infection. Infection is thought to occur orally among newborn lambs and any cohort adult sheep or lambs that may come in contact with the infected material (Dickinson et al., 1974; Hourrigan et al., 1979). PrPSc has been found in the placenta (Andréoletti et al., 2002; Onodera et al., 1993; Race et al., 1998; Tuo et al., 2002; Tuo et al., 2001), and various other tissues (Andréoletti et al., 2000; Heggebø et al., 2000; Jeffrey et al., 2001a,b; Race et al., 1998; Keulen et al., 1996Keulen et al., 1999). These studies did not include tests for infectivity. Infectivity of the placenta was shown in an oral dosing experiment in 1972 where placenta was given to sheep and goats (Pattison et al., 1972). Experimental transmission of scrapie to sheep and goats using infected brain tissue has also been shown (Foster et al., 2001; Pattison and Millson, 1961). There have been unsuccessful attempts to identify the scrapie agent in blood (Hadlow et al., 1974; Hadlow et al., 1982; Hadlow et al., 1980; Pattison and Millson, 1962a,b), but in 2002 the transmission of scrapie was achieved with whole blood transfusion and a buffy coat transfusion (Hunter et al., 2002).
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 (Beekes and McBride, 2000; Beekes et al., 1998; Heggebø et al., 2000; Kimberlin and Walker, 1989; Keulen et al., 1999). PrPSc then moves onward to the tonsil, spleen, retropharyngeal lymph nodes, mesenteric lymph nodes, and peripheral nervous tissue (Mabbott and Bruce, 2001; Maignien et al., 1999; Press et al., 2004). 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 (Eklund et al., 1967; Hadlow et al., 1974; Hadlow et al., 1982; Hadlow et al., 1980; Hadlow et al., 1979).
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. The ataxia can include 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. This may lead to wool loss especially over the hindquarters and lateral thorax. This clinical sign is also the origin of the term ‘scrapie’. 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. (Bradley, 1997; Dickinson, 1976; Kimberlin, 1981; Palmer, 1976; Parry and Oppenheimer, 1983; Radostits et al., 2000). Affected animals may live one to six months after onset of clinical signs (Capucchio et al., 2001; Foster et al., 2001a,b,c; USDA, 2005). It is also important to note that some scrapie-infected sheep may appear healthy if left undisturbed, but the stress of transport, shearing, or pregnancy may bring on clinical signs (Detwiler and Baylis, 2003).

Impact: Economic

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Scrapie is classified as a notifiable disease by the World Organization for Animal Health (OIE); transmissible diseases that are considered to be of socioeconomic and/or public health importance within countries and that are significant in the international trade of animals and animal products (OIE, 2005). The presence of scrapie in sheep-producing countries prevents the export of breeding stock, semen, and embryos to many other countries. For example the American Sheep Industry Association estimates that scrapie costs the industry over US $20 million each year in lost export sales, disposal costs for offal, and lost productivity (National Institute for Animal Agriculture, 2005).

Zoonoses and Food Safety

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The European Food Safety Authority (EFSA) and the European Centre for Disease Prevention and Control (ECDC) reviewed the evidence for links between animal and human TSEs. They concluded that, at present, the only TSE agent demonstrated to be zoonotic is the classical BSE agent (EFSA Panel on Biological Hazards, 2011).

Disease Treatment

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No effective treatment is available for scrapie, and the condition is fatal.

Prevention and Control

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Until relatively recently, scrapie has been a difficult disease to control. The lack of a live animal test that would allow for large scale flock screening has meant that infected animals are not identified until clinical disease appears: epidemiological studies are also hampered.

The potential for PrP genotyping to control scrapie started to emerge in the 1990s when case control studies demonstrated clear linkage between scrapie risk and PrP genotype in several breeds of sheep in Britain (Hunter et al., 1997). The signi?cant polymor­phisms linked to disease risk are at codons 136 (alanine/valine), 154 (arginine/histidine), and 171 (glutamine/histidine/arginine) of the ovine PrP gene. Combinations of these poly­morphisms produce ?ve commonly seen PrP haplotypes or alleles – ARR, AHQ, ARH, ARQ and VRQ – not all breeds carry all alleles – with the potential to generate up to 15 genotypes.

Genotyping has been used in two main ways. Firstly, selective breeding programmes have operated in several EU Member States in the last decade, whereby rams are genotyped and then selected for breeding to reduce disease risk in their progeny. This programme requires negative selection of VRQ (and sometimes ARQ) carriers and positive selection for ARR. Secondly, whole flock genotypoing can be targeted at affected flocks, with selective culling of high risk genotypes and leaving a resistant population.

Application of a combination of these programmes in Great Britain since 2002 (Dawson et al., 2008), has seen a steady reduction in estimates of prevalence, as judged by ongoing active surveillance of fallen stock and healthy slaughter sheep. (see: AHVLA, Sheep TSE surveillance statistics (Great Britain).


Husbandry methods and good practice


Husbandry methods such as constructing lambing pens from straw bales and destroying them after each lambing, and moving sheep to clean paddocks in small groups will reduce the risk of cross contamination. Cross infection can be reduced by using several lambing areas separated from each other. Producers should pick up the placenta and clean bedding contaminated with placental fluids and tissues after lambing to minimize scrapie transmission. Intensive production methods appear to increase the spread of the disease.


Farm-level control


Scrapie infection can be minimized 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 (CFIA, 2005; Dawson et al., 1998; European Commission, 2001; US Department of Agriculture, 2005).

Codon 136: sheep homozygous for alanine (AA) have been shown to be more resistant to scrapie than sheep homozygous for valine (VV) or heterozygous (AV) in European studies. AA sheep in Europe do have a lower incidence of scrapie but they are not completely resistant to scrapie. In sheep in the USA differences at codon 136 are less important than in European sheep, which may be due to differences in the strain of scrapie agent in the two regions.

Codon 154: changes at this codon, arginine (R) or histidine (H) appear to be less important than either the other two codons, and screening sheep for differences at this codon has little value for determining resistance.

Codon 171: amino-acid changes at this codon have a large effect on susceptibility in sheep in both the USA and Europe. Scrapie is very rare in sheep homozygous for arginine (RR) at this codon (a case in a Suffolk in Japan has been reported: Ikeda et al., 1995). The frequency of heterozygous (QR) sheep is low among sheep with scrapie, whereas the frequency of scrapie-infected sheep homozygous for glutamine (QQ) is high (Thomas, 2001).

Therefore the most susceptible genotypes are VV136, RR154, QQ171 and VA136, RR154, and QQ171. Scrapie frequently occurs in AA136, RR154, QQ171 in Suffolk sheep, whereas AA136, RR154, and RR171 confer resistance in all breeds.


National and international control policies


Many countries where scrapie is endemic, including the UK, USA, EU, Iceland and Canada have implemented national control programmes to eradicate scrapie (CFIA, 2005; DEFRA, 2001; European Commission, 2003a,b; Thorgeirsdottir et al., 2002; USDA, 2005). Some countries such as the UK and The Netherlands, and several countries of the EU use genetic selection as their primary means of scrapie control (Drögemüeller et al., 2001; Pluimers, 2004; Sipos et al., 2002). 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 (DEFRA, 2001).

Regulation (EC) No 999/2001 of the European Parliament and the Council of the European Union lays down rules for the prevention, control and eradication of transmissible spongiform encephalopathies in animals. [See also, Summaries of EU legislation: Transmissible Spongiform Encephalopathies (TSEs)]

The Scrapie Flock Certification Programme in the USA assigns status to flocks having no evidence of scrapie, thereby providing a source of scrapie-free breeding animals (US Department of Agriculture, 2005). In the USA, sheep of high risk genotypes are also removed from the flock or their movement is restricted. Sheep from infected and source flocks are often depopulated in an effort to eliminate disease. Producers receive compensation by the Federal government for animals that must be removed from the flock. Iceland also uses a combination of genetic selection and depopulation of infected and source flocks for scrapie control (Thorgeirsdottir et al., 2002).

BSE of cattle has been linked to the practice of incorporating rendered ruminant byproducts into cattle feed. 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). This ban was adopted by the EU in 1994 and in the USA in 1997 (European Commission, 2001; FDA, 1997).

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Distribution References

Bildfell R, Brocklebank J, Doherty T, Bellamy C, 1991. Scrapie in Prince Edward Island. Canadian Veterinary Journal. 32 (7), 438.

CABI, Undated. Compendium record. Wallingford, UK: CABI

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Links to Websites

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WebsiteURLComment
National Scrapie Education Initiative (USA)http://www.eradicatescrapie.org/Website containing general information about scrapie, and the scrapie eradication programme. The website is provided by the National Institute for Animal Agriculture.
Reference Laboratory for BSE and Scrapie, University of Bernhttp://www.vetsuisse.unibe.ch/neurocenter/content/reference_laboratory_for_bse_and_scrapie/index_eng.html
Scrapie - AHVLA (UK)http://www.defra.gov.uk/ahvla-en/disease-control/notifiable/scrapie/Information on diagnosis, disease control, legislation and the National Scrapie Plan (NSP)
Scrapie - Canadian Food Inspection Agencyhttp://www.inspection.gc.ca/animals/terrestrial-animals/diseases/reportable/scrapie/eng/1329723409732/1329723572482Information for producers and the livestock sector in Canada.
Scrapie Information - USDA-APHIShttp://www.aphis.usda.gov/animal_health/animal_diseases/scrapie/Summarises the USDA-APHIS Scrapie Program. Contains factsheets, diagnostic illustrations and information directed at vets, producers and others involved with scrapie-affected animals.

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