BSE / MAD COW DISEASE PICTURES: prions spreading from cows to humans

Scheme of the possible transmission routes of BSE prions from cows to the human brain. The image above is 400 pixels across and the original is 3,017 pixels across.

This simplified diagram shows the likely routes of BSE prions from their amplification through cows to their entry to the human brain. The prions are represented by the purple particles streaming around the picture. At top left "O" represents the origin of BSE prions. This has not been established with certainty. The prions are then shown passing from one cow to another (BSE infected cattle were fed to other cows). Contaminated meat (and possibly other bovine derivatives) then carried the prions to humans. In the human gut (bottom left) prions may be taken up by lymphoid tissues (Peyer's patches). The prions are then ferried around the body in lymphocytes "L". Prion replication is thought to occur in lymphoid tissues, especially the spleen "S". Nerves "N" that supply the lymphoid tissues then allow prions to travel back up them to the brain. Since lymphocytes carry prions, it is reasonable to assume that transport to the brain might occur in parallel through the blood. This is illustrated at "B". The fear that human blood and blood products may carry BSE prions has caused many countries to ban blood donations from those who are deemed to have been exposed.