It is thought that the infective material may originate in meat products from infected cows and sheep (particularly brains and spinal cords) although there is is only circumstantial evidence of this. The overwhelming majority of CJD cases occur sporadically and with no clue as to how they are transmitted. There are fears with as yet no factual basis that CJD could spread via blood transfusion.
The prevailing belief is that spongiform diseases are caused by rogue proteins known as prions that are thought to be abnormal variants of the prion proteins normally present on the surface of nerve cells. The disease causing prions are believed to convert their normal counterpart protein into the abnormal form. Normal prion protein is produced by a gene that is widely found in nature, but its function is unknown. Prions lack the DNA and RNA that are the hereditary material of other transmissible disease agents. The prion theory is based on the work of Stanley B. Prusiner of the University of California at San Francisco.
In 1996 an expert British committee identified a cluster of 10 cases of a variant of Creutzfeldt-Jakob disease in people younger than 42, some in their teenage years. The committee concluded it was dealing with a variant form because of the unusual microscopic appearance of diseased neurons. The committee said that although scientific proof was lacking, it was tentatively linking the cluster to mad cow disease.
It was announced in 1997 that Swiss scientists had found an antibody to the aberrant protein found in "mad cow disease" and CJD in humans. The antibody ignores normal prion protein (PrP) and latches onto the misfolded PrP from brains of cows with bovine spongiform encephalopathy, from mice with a prion disease called scrapie, and from CJD victims. The new antibody may recognize the dangerous PrP because it attaches to three different regions of the protein -- regions which are distant from one another in the normal conformation, but are close together in the misfolded aggregate.
In 1994, it was reported that at least two young British women have CJD and two middle-aged dairy farmers died of the disease within the previous 12 months. One UK doctor believes that consumption, even in small doses, is cumulative and predicts that at least one beef eater in 10 may develop CJD unless humans develop immunity.
Up to March 1996, ten cases of a new variant of Creutzfeldt-Jakob disease had been reported in the United Kingdom, linked to exposure to the agent of bovine spongiform encephalopathy in meat products. Cases of bovine spongiform encephalopathy have declined since 1993, and the epidemic of bovine spongiform encephalopathy is expected to disappear in the United Kingdom by the year 2001. By 1999, 46 people had died of the disease.