What causes progressive neurological diseases such as mad-cow disease or vCJD?
vCJD is caused by an unusual protein called a prion (proteinaceous infectious particle). Prions are found in the brains of cows with mad-cow disease and in the brains of humans with vCJD. Prions can also be found in the spinal cord and in the back of the eye (retina). However, blood from infected animals or blood from infected people has never been shown to be a source of infection to humans. If prions are found only in the brain and spinal cord, why did people in England get vCJD after eating meat from cows? The likely source of prions for people in England was hamburger, not steak, prepared from cows. Hamburger may be prepared in a manner that includes the spinal cord. Steak, on the other hand, represents only the muscles of cows and, therefore, does not contain prions. Why do vaccines contain materials derived from cows? Viral vaccines are weakened forms of natural viruses. Some viral vaccines are made by growing viruses in specialized cells in the laboratory. Many growth factors ar
