In addition to hearing about mad cow disease, you may have also heard about foot-and-mouth disease, also commonly referred to as hoof-and-mouth disease. Read more about it in this Question of the Day
The Prion Hypothesis
Prions are proteins that are found in the nerve cells of all mammals. Numerous prions are in each nerve cell, but no one knows for sure what the prion protein does. As mentioned above, many abnormally-shaped prions are found in the brains of BSE-infected cows and humans afflicted with nvCJD or CJD. So, the prion hypothesis goes like this:
- An person ingests an abnormally-shaped prion from contaminated food.
- The abnormally-shaped prion gets absorbed into the bloodstream and crosses into the nervous system.
- The abnormal prion touches a normal prion and changes the normal prion's shape into an abnormal one, thereby destroying the normal prion's original function.
- Both abnormal prions then contact and change the shapes of other normal prions in the nerve cell.
- The nerve cell tries to get rid of the abnormal prions by clumping them together in small sacs that merge with its "stomach" (lysosome).
- Because the nerve cells cannot digest the abnormal prions, they accumulate in the lysosomes.
- The lysosomes grow and engorge the nerve cell, which eventually dies.
- When the cell dies, the abnormal prions are released to infect other cells.
- Large, sponge-like holes are left where many cells die.
- Numerous nerve cell deaths lead to loss of brain function, and the person eventually dies.
Further research in this area may eventually reveal the nature of the BSE-causing agent.
Animal and Human Consequences
Cows infected with BSE lose weight, show abnormal behavior (skittishness), may become paralyzed and die. Humans afflicted with nvCJD begin with psychiatric problems (paranoia) or perhaps problems with their senses. They later develop problems in muscle coordination (balance, speech), muscle spasms, problems with their senses (hearing, vision) and memory loss. They may finally lapse into coma and die.