Test for ‘Mad Cow Disease’ Developed
The first test that can accurately diagnose “mad cow disease” and related disorders in living humans and animals has been developed by researchers at Caltech and the National Institute of Neurological Disorders and Stroke.
Mad cow disease, more properly known as bovine spongiform encephalopathy (BSE), has been epidemic in cattle herds in Britain recently, and the agent that causes it is suspected in a similar disorder in at least 13 people who have eaten infected beef.
Wholesale destruction of herds of cattle in Britain has been necessary because veterinarians have had no way to distinguish healthy animals from infected ones.
The new test, described today in the New England Journal of Medicine, could eventually provide an accurate way to identify cows that must be killed to halt the spread of the disease, while permitting cattle breeders to retain their healthy animals, according to Caltech biologist Michael G. Harrington, who developed the test.
It can also be used to identify the related disorders, Creutzfeldt-Jakob disease and kuru, which strike about one to two people per million worldwide. The diseases, which kill brain cells, are usually fatal within four to six months after the onset of symptoms, which include muscle spasms, difficulty in walking and dementia.
Although there is no treatment yet for these disorders, the test will allow doctors to distinguish them from Alzheimer’s disease, which has a completely different prognosis.
The test “is a welcome step forward,” according to Dr. John Collinge of the Imperial School of Medicine in London. It “appears to be highly specific and sensitive,” he added, but further studies with larger numbers of patients will be necessary for researchers to be confident about its use.
“We hope this will be the first step in producing a commercially available test that will detect [the diseases] in humans and animals,” said Zach W. Hall, director of the National Institute of Neurological Disorders and Stroke in Bethesda, Md. “Such a test would be enormously useful in helping to find sound solutions to the current crisis.”
A German team is expected to publish Saturday a description of a similar test for BSE. Some British experts reportedly are upset that the new tests were developed in the United States and Germany and not in Britain, where the disorder has played havoc with the cattle industry.
The outbreak of mad cow disease has led to a European ban on British beef imports and the slaughter of 170,000 cows. As many as 4.5 million more are expected to be slaughtered at the rate of 15,000 per week over the next five to six years--at a cost of $700 million.
Even the cause of the disorder is controversial. The prevailing theory is that it is caused by a protein called a prion (pronounced PREE-on), which would make the diseases unique. All other infectious diseases are caused by organisms containing either DNA or RNA, the materials normally used to store genetic information.
Because no one has determined how a protein could carry genetic information, some scientists believe that the disorders are spread by viruses--even though no evidence of such agents has been found.
For the test developed by Harrington and his colleagues, the cause of the disorder is irrelevant. Instead, they are looking for byproducts of damage to the brain caused by the agent, whatever it may be.
They focus on a protein called 14-3-3, which is found normally in brain cells and some other cells around the body, but not in cerebrospinal fluid, the liquid that bathes the brain and the spinal cord.
When brain cells are destroyed by the disease, 14-3-3 leaks into the spinal fluid. The group has developed what Harrington calls “a straightforward test that can be performed by anyone who reads the [research] paper.”
In humans, the test cannot be used for general screening for the diseases, Harrington noted. It has a high degree of accuracy only when the patient already displays some clinical symptoms, such as dementia. But it could be very useful for distinguishing the encephalopathies from other disorders, said Dr. Clarence J. Gibbs Jr. of the neurological disorders institute, a co-developer.
“If a patient has Creutzfeldt-Jakob disease, [the physician must] advise the family that the patient will die within a year,” he said. “If it’s Alzheimer’s, you tell them that it will be a long, drawn-out affair.”
The test could also be useful on animals. Now, if a cow shows any symptoms of mad cow disease, it must be destroyed immediately. Autopsies have shown, however, that a third of the animals killed did not have the disease, Harrington said. If the test could be used to determine which ones are actually infected, it could save substantial numbers of animals, as well as money, he said.
And if it could be adapted for screening all of Britain’s older cows--which are most at risk of having the disorder--the savings could be greater, he added.
