It was named after two German psychiatrists, Hans Gerhard Creutzfeldt and Alfons Maria Jakob. CJD is classified as a transmissible spongiform encephalitis (TSE). Spongiform refers to the description of the infected brain, which becomes filled with so many holes that it resembles a sponge. There are four forms of CJD: sporadic, which arises spontaneously; familial, or inherited; infective (very rare), which is passed on by pituitary growth hormone obtained from cadavers or through contaminated surgical instruments; and a new variant of CJD (v-CJD), linked to "mad cow disease." Besides CJD, there are four other TSEs that affect people: kuru, which was found in an isolated tribe in Papua New Guinea; Gerstmann-Sträussler-Scheinker syndrome (an inherited condition); fatal familial insomnia (an inherited condition); and sporadic fatal insomnia. These diseases are very rare. CJD itself occurs only in 1 case per 1 million people. In the U.S., about 200 cases are reported each year.

Symptoms of classic CJD typically appear about age 60. Symptoms of new variant CJD (v-CJD) or of CJD caused by contaminated pituitary growth hormone can first appear in the early 20s to early 40s. About 9 in 10 people die within a year of symptoms.

But these symptoms are the same as for other forms of dementia or illness, which makes it difficult to diagnose. Other symptoms of CJD include behavioral changes and visual disturbances. As the disease gets worse, symptoms include mental deterioration, involuntary movements, blindness, weakness of limbs, and coma.

The exact cause is still under investigation, but most researchers believe that CJD is caused by an abnormal prion, which is a particular kind of protein. Normal prions are harmless and found in every cell in the body. Abnormal prions take a slightly different shape and clump together in fibers and plaques. Researchers aren't sure what role these fibers and plaques play in CJD. In up to 3 in 20 CDJ cases, the abnormal prion has been inherited.

CJD is not a sexually transmitted infection, nor is it a contagious one. It cannot be passed from one person to another. People in the same household as a person with CJD will not get the disease. The FDA now bans blood donations from people who have spent an extended time in England or Europe because of concerns that CJD may be passed through blood products. But there is no documented case in which prions have been passed through blood products. The only proven manner in which CDJ has been passed on from an infected person is through contaminated tissue (a cornea, for example) or contaminated surgical instruments. Normal sterilization procedures such as cooking or boiling do not destroy prions.

In a brain biopsy, a neurosurgeon removes a small piece of the brain to be examined. But a biopsy has several drawbacks. The procedure may be dangerous for the patient, and the brain sample removed may not be a part that's affected by CJD. Researchers have developed a safer test, which looks for a particular protein in a patient's cerebrospinal fluid, but this test is not yet commercially available. An autopsy after death can also confirm the illness.

Currently, there is no treatment for CJD. Medicine is given to relieve symptoms, but does not change the course of the disease. It is always fatal.

BSE and CJD are similar but not the same. BSE is a progressive nervous system disorder in cattle similar to a disease in sheep called scrapie. BSE has been found mainly in cattle in the United Kingdom, but also in other areas of Europe. It has not been found in U.S. cattle, according to the USDA. The USDA has banned the importation of beef from England and Europe to prevent bringing in contaminated meat. Researchers believe that BSE may be caused by feeding scrapie-infected sheep meat-and-bone meal to cattle. They also believe that a new form of CJD in people called v-CJD, which first showed up in England in the early 1990s, is caused by eating beef contaminated by BSE. (Cooking the meat does not destroy the prions believed to cause the disease.) The new variant CJD differs from CJD in that people who have it are typically much younger (30 versus 60) and that symptoms are more psychiatric and sensory than neurological.

The FDA and several advisory committees have determined that the risk of contracting v-CJD through any vaccine (for polio or hepatitis, for example) is remote. The concern about vaccines surfaced because some vaccines are made using substances derived from cattle. Some of the bovine components have come from countries where BSE is found. But there is no evidence in Europe that any vaccines have caused v-CJD.