BSE Transmission: Not in Blood, Spread via Contaminated Feed and Tissues

Correction: BSE prions are present in blood at very low titers (detectable by PMCA/RT-QuIC), and blood transfusion has transmitted vCJD (4 UK cases). However, the primary natural route is oral via contaminated feed.

Transmission Pathways

• Oral (cattle): Meat-and-bone meal (MBM) containing CNS tissue from infected animals. Main driver of epidemic.
• Oral (humans): BSE-contaminated beef products (mechanically recovered meat, gelatin).
• Blood transfusion: 4 vCJD cases from asymptomatic donors (UK). Leukoreduction reduces but may not eliminate risk.
• Iatrogenic: Contaminated surgical instruments, dura mater grafts, hGH (historical).
• Not transmitted by: Milk, muscle meat (if SRM removed), casual contact, aerosols.

Prion Distribution in Cattle

High: brain, spinal cord, dorsal root ganglia, trigeminal ganglia, retina, distal ileum, tonsil.
Low/undetectable: blood, muscle, milk, hide (with current assays).

Control Measures

• Feed ban (ruminant protein → ruminants).
• SRM removal at slaughter.
• Blood donor deferral for at-risk residency.
• Prion-reduction filtration for blood products (some countries).

Understanding tissue distribution guides food safety and medical device policies.