The classic form of Creutzfeldt-Jakob disease, or CJD, is an infectious disease that causes progressive brain damage and death. New variant Creutzfeldt-Jakob disease, or nvCJD, is a slightly different form of CJD. The new variant of CJD is most likely the human form of mad cow disease.

What is going on in the body?

Both classic and new variant CJD are prion diseases. Prions are a modified form of a protein found on normal cell surfaces. Both diseases cause a buildup of prions in the brain. The increase in prions causes brain injury and degeneration. The same type of prion may cause both mad cow disease and nvCJD.

The classic form of CJD may cause symptoms 15 months to 30 years after exposure. New variant CJD may take 5 to 10 years to develop after the person has been exposed to the prion.

What are the causes and risks of the disease?

There are three main causes for classic CJD. Inherited CJD runs in families and is caused by a mutation in the gene coding for the normal prion protein. Sporadic CJD has no known genetic or infectious cause.

Creutzfeldt-Jakob disease through infection is transmitted by prions. The individual is infected through direct or indirect contact with body tissues of an infected person. Following are some examples of this transmission:

There is a strong link between mad cow disease and the new variant of CJD. Most scientists believe that this new variant CJD is the human form of mad cow disease. It is believed that the abnormal prion is transmitted from infected cattle to humans when the person eats meat or beef products. Milk and dairy products from infected cattle don't appear to transmit the disease.

At the present time, infected cattle are found mostly in Europe, particularly the United Kingdom. Even in the UK, the risk of getting nvCJD from eating infected beef is only about 1 case per 10 billion servings.

The classic form of Creutzfeldt-Jakob disease is most common in people from 50 to 75 years of age. New variant CJD is seen most often in teens and young adults.