‘Mad Cow Disease’ in People Is Traced to Beef
The first direct evidence that “mad cow disease” has been transmitted to humans through the consumption of infected beef was reported Thursday in the British journal Nature.
Researchers from the Imperial College School of Medicine in London have found that biochemical traces of an infectious agent from people with a rare form of Creutzfeldt-Jakob disease (CJD) are identical to such traces from cows.
At least 13 people in Britain have developed this form of CJD, which has long been suspected to be caused by an unusual infectious agent, called a prion, from the diseased animals. But researchers previously had been unable to prove their suspicions.
Dr. John Collinge and his associates report that they have developed a new biochemical test for prions--similar to the technique used for DNA fingerprinting.
The team found that the biochemical fingerprints of prions from patients with the rare form of CJD are identical to those of prions from laboratory animals infected by cows with the disease.
The fingerprints are completely different, however, from those of prions from patients with inherited or sporadic CJD not linked to the recent outbreak.
The research represents “an exciting new approach” to tracking the cause of human cases, said molecular biologist Charles Weissmann of the University of Zurich.
“This is very strong evidence supportive of a direct link between these diseases” in humans and animals, said Caltech biologist Michael G. Harrington. “I’m convinced.”
Harrington last month reported the development of a test that indicates whether an animal or human has been infected by prions, but that test is not able to distinguish among various strains of the agent. The new test can identify a specific strain.
Mad cow disease, more formally known as bovine spongiform encephalopathy or BSE, has been endemic in British cattle herds since the 1980s.
The disease is closely related to the human diseases CJD and kuru, which strike one to two people per million worldwide each year. The diseases kill brain cells and are usually fatal within four to six months after the onset of symptoms, which include muscle spasms, difficulty in walking and dementia.
All the diseases are caused, most scientists now agree, by the family of proteins called prions (pronounced PREE-ons). This makes them unique because all other infectious diseases are caused by organisms containing either DNA or RNA, the materials normally used to store genetic information (proteins do not contain DNA or RNA).
With their test, Collinge’s group found that each prion strain produces a unique biochemical pattern.
They then studied brain tissue from 26 humans with CJD. The pattern they obtained was the same in tissue from all the patients with the new form of CJD.
