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Bovine Spongiform Encephalopathy (BSE) in Cattle


Introduction

Bovine Spongiform Encephalopathy (BSE), commonly known as “mad cow disease,” is a progressive, fatal neurodegenerative disease of cattle. It belongs to a group of disorders known as transmissible spongiform encephalopathies (TSEs). BSE is of major veterinary and public health importance due to its association with variant Creutzfeldt-Jakob disease (vCJD) in humans.

Etiology
Causative Agent

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

Agent Characteristics
  • Proteinaceous infectious particles (no nucleic acid)
  • Highly resistant to heat, radiation, and conventional disinfectants
  • Capable of inducing conformational changes in normal proteins
  • Accumulate primarily in nervous tissue
Epidemiology
Species Affected
  • Cattle (primary species)
  • Other species may be affected experimentally or through exposure (e.g., cats, zoo animals)
Transmission
  • Ingestion of contaminated meat-and-bone meal (MBM) containing infected tissues
  • No significant horizontal transmission between live animals under natural conditions
Risk Factors
  • Feeding ruminant-derived protein to cattle
  • Inadequate feed controls
  • Exposure to contaminated feed sources
Incubation Period
  • Long incubation period (typically 2–8 years)
Pathogenesis
Entry and Absorption

Prions are ingested and absorbed through the gastrointestinal tract, particularly via Peyer’s patches.

Neural Spread
  • Transport via peripheral nerves to the central nervous system
  • Accumulation in brain and spinal cord
Neurodegeneration
  • Spongiform changes (vacuolation) in brain tissue
  • Neuronal loss and gliosis
  • No inflammatory response
Clinical Signs
Behavioral Changes
  • Nervousness and anxiety
  • Hyperesthesia (increased sensitivity to stimuli)
  • Aggression or excitability
Neurological Signs
  • Ataxia (incoordination)
  • Difficulty rising
  • Tremors
  • Abnormal gait
General Signs
  • Weight loss despite normal appetite
  • Decreased milk production
Disease Course
  • Progressive deterioration over weeks to months
  • Always fatal
Summary for Practitioners

BSE should be suspected in adult cattle with progressive neurological signs and behavioral changes, especially in regions with a history of the disease.

Postmortem Findings
Gross Lesions
  • No significant gross lesions
Microscopic Lesions
  • Spongiform degeneration (vacuolation) in gray matter
  • Neuronal loss
  • Astrocytosis (gliosis)
  • Accumulation of prion protein in brain tissue
Diagnosis
Clinical Diagnosis

Based on neurological signs and history; however, definitive diagnosis requires laboratory testing.

Laboratory Diagnosis
  • Postmortem examination of brain tissue
  • Immunohistochemistry for prion protein detection
  • Western blot or ELISA for prion identification
Differential Diagnosis
  • Rabies
  • Listeriosis
  • Hypomagnesemia (grass tetany)
  • Nervous ketosis
  • Other encephalopathies
Summary for Practitioners

BSE is a notifiable disease. Suspected cases must be reported to veterinary authorities for investigation.

Treatment
General Approach

There is no treatment for BSE.

Management
  • Immediate reporting and quarantine
  • Culling of affected animals
  • Proper disposal of carcasses
Summary for Practitioners

BSE is fatal and untreatable. Control depends entirely on prevention and regulatory measures.

Control and Prevention
Feed Regulations
  • Ban on feeding ruminant-derived protein to cattle
  • Strict monitoring of feed production
Surveillance
  • Active and passive surveillance programs
  • Testing of high-risk animals
Specified Risk Material (SRM) Removal
  • Removal of high-risk tissues (brain, spinal cord) from food chain
Biosecurity
  • Traceability of animals and feed sources
  • Control of animal movement
Summary for Practitioners

Strict feed controls and surveillance programs have been effective in reducing BSE incidence globally.

Zoonotic Importance

BSE is zoonotic and is associated with variant Creutzfeldt-Jakob disease (vCJD) in humans, linked to consumption of contaminated beef products.

Economic Importance

BSE has caused major economic losses due to trade restrictions, culling programs, reduced consumer confidence, and extensive control measures.

Summary

Bovine Spongiform Encephalopathy is a fatal prion disease of cattle characterized by progressive neurological degeneration. It has significant veterinary and public health implications, and control relies on strict feed regulations and surveillance.