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Scrapie in Sheep and Goats

Introduction

Scrapie is a chronic, progressive, and fatal neurodegenerative disease of sheep and goats. It belongs to the group of transmissible spongiform encephalopathies (TSEs), similar to Bovine Spongiform Encephalopathy (BSE) in cattle. The disease is characterized by behavioral changes, intense pruritus (itching), neurological dysfunction, and eventual death. Scrapie has significant economic and regulatory importance in small ruminant production systems.

Etiology
Causative Agent

Scrapie is caused by abnormal prion proteins (PrPSc), which are misfolded forms of the normal cellular prion protein (PrPC).

Agent Characteristics
  • Proteinaceous infectious particle (no nucleic acid)
  • Highly resistant to heat, disinfectants, and environmental degradation
  • Capable of inducing conformational change in normal prion proteins
  • Accumulates in nervous and lymphoid tissues
Epidemiology
Species Affected
  • Sheep (primary host)
  • Goats (also affected)
Transmission
  • Primarily via ingestion or contact with contaminated environment
  • Placental and birth fluids are major sources of infection
  • Horizontal transmission between animals
Genetic Susceptibility
  • Susceptibility influenced by prion protein (PRNP) gene variants
  • Certain genotypes are more resistant or susceptible
Incubation Period
  • Long incubation period (typically 2–5 years)
Risk Factors
  • Contaminated lambing/kidding areas
  • Mixing of infected and susceptible animals
  • Lack of genetic selection for resistance
Pathogenesis
Entry and Initial Replication

Prions are ingested and initially replicate in lymphoid tissues such as Peyer’s patches.

Neural Spread
  • Spread via peripheral nerves to the central nervous system
  • Accumulation in brain and spinal cord
Neurodegeneration
  • Spongiform changes in brain tissue
  • Neuronal loss and gliosis
  • No significant inflammatory response
Clinical Signs
Behavioral Changes
  • Apprehension
  • Changes in temperament
  • Isolation from flock
Pruritic Form (Classical Scrapie)
  • Intense itching
  • Rubbing against objects (“scraping” behavior)
  • Wool loss and skin damage
Neurological Signs
  • Ataxia
  • Tremors
  • Incoordination
  • Difficulty standing or walking
General Signs
  • Weight loss despite normal appetite
  • Progressive weakness
Disease Course
  • Slow progression over months
  • Always fatal
Summary for Practitioners

Scrapie should be suspected in adult sheep or goats showing progressive neurological signs and pruritus, especially in flocks with a history of the disease.

Postmortem Findings
Gross Lesions
  • No significant gross lesions
Microscopic Lesions
  • Spongiform degeneration (vacuolation) of neurons
  • Neuronal loss
  • Astrocytosis (gliosis)
  • Accumulation of prion protein in brain and lymphoid tissues
Diagnosis
Clinical Diagnosis

Based on clinical signs and flock history; confirmation requires laboratory testing.

Laboratory Diagnosis
  • Postmortem examination of brain tissue
  • Immunohistochemistry for prion detection
  • ELISA or Western blot for prion protein
  • Rectal biopsy (in live animals) for lymphoid tissue testing
Differential Diagnosis
  • Listeriosis
  • Coenurosis (gid)
  • Hypomagnesemia
  • Other neurological diseases
Summary for Practitioners

Scrapie is a notifiable disease in many countries. Suspected cases must be reported to veterinary authorities.

Treatment
General Approach

There is no treatment for scrapie.

Management
  • Culling of affected animals
  • Flock monitoring and control measures
Summary for Practitioners

Scrapie is fatal and untreatable. Control relies on prevention and flock-level management.

Control and Prevention
Genetic Selection
  • Breeding for resistant genotypes (e.g., ARR allele in sheep)
Biosecurity
  • Avoid introduction of infected animals
  • Quarantine and test new stock
Management Practices
  • Proper disposal of placentas and carcasses
  • Cleaning and disinfection of lambing areas (limited effectiveness due to prion resistance)
Surveillance Programs
  • National control and eradication programs
  • Monitoring and reporting of cases
Summary for Practitioners

Control programs emphasize genetic resistance, surveillance, and strict flock management practices.

Zoonotic Importance

Scrapie is not considered zoonotic and has not been linked to disease in humans.

Economic Importance

Scrapie leads to economic losses due to culling, reduced productivity, trade restrictions, and costs associated with control programs.

Summary

Scrapie is a fatal prion disease of sheep and goats characterized by neurological dysfunction and pruritus. Control depends on genetic selection, biosecurity, and surveillance measures.