BSE: Prion Cause, Transmission via Contaminated Feed, and Clinical Signs

Bovine spongiform encephalopathy (BSE) is caused by a misfolded prion protein (PrP^Sc), not a bacterium or virus.

Transmission

• Primary: Cattle fed meat-and-bone meal (MBM) containing infected CNS tissue.
• Not horizontal: No cow-to-cow spread via contact, aerosols, milk.
• Maternal: Rare, low risk (calves from infected dams).
• Iatrogenic: Contaminated instruments (theoretical).

Clinical Signs

• Behavioral: nervousness, aggression, separation from herd.
• Motor: ataxia, hypermetria, tremors, falling.
• Sensory: hyperesthesia to touch/sound.
• Autonomic: reduced rumination, weight loss.
• Progression: weeks to months; always fatal.

Diagnosis

Post-mortem: rapid ELISA/IHC on obex; confirmatory Western blot (diglycosylated-dominant pattern).

Prevention

• Ruminant feed ban.
• SRM removal (brain, spinal cord, eyes, tonsils, distal ileum).
• Age-based testing at slaughter.
• Traceability.

These measures have reduced classical BSE to near zero worldwide.