NEW YORK (Reuters) -- For the first time, researchers have developed a test for a group of animal and human diseases that have caused a furor around the world and led to the collapse of the $6.5 billion British beef industry.
The test picks up transmissible spongiform encephalopathies (TSE), which include Creutzfeldt-Jakob disease (CJD), a fatal degenerative disorder in humans. And it may determine if British cows slated for the slaughterhouse do indeed have bovine spongiform encephalopathy (BSE), a TSE responsible for "mad cow" disease.
However, the test does not determine if humans can contract CJD from eating contaminated beef, as has been postulated. Nor can it determine if people who may have eaten such meat will develop CJD in the future.
According to the report in this week's issue of The New England Journal of Medicine, the test detects a brain protein called 14-3-3. Although present throughout much of the body, 14-3-3 is concentrated in the brain and is released into cerebrospinal fluid in patients with CJD.
The test was able to accurately detect CJD in 68 out of 71 people with the disease -- a sensitivity of 96%. And the test gave false positives for only 4 out of 94 people with other brain disorders, such as stroke or Alzheimer's disease -- a specificity of 96%.
When the researchers excluded people who had had strokes in the month before the test, the specificity of the test was even higher at 99%, according to a research team from the National Institute of Neurological Disorders and Stroke (NINDS) in Bethesda, Maryland, and the California Institute of Technology in Pasadena.
"Any test arising from our work would be best applied to patients already suspected of having CJD, for example, those with rapid onset dementia," according to a statement from one study author, Dr. Clarence J. Gibbs, the acting chief of the NINDS Laboratory of Central Nervous System Studies. "A finding of 14-3-3 in the cerebrospinal fluid of such a patient would strongly suggest a diagnosis of CJD, and would rule out other dementing disease such as Alzheimer's disease."
The rapid neural degeneration caused by CJD usually takes four to six months, starting with dementia and progressing to coma and death. An autopsy reveals large spongy holes in the brain -- previously the only way to conclusively diagnose CJD and other disorders.
In Great Britain, a handful of cases of CJD in young adults are suspected -- but have not been proven -- to be caused by eating TSE-contaminated beef. Many experts believe the causative agent is neither a bacteria nor a virus, but an agent previously unknown to science -- a prion (pronounced pree-on) or infectious protein. It is not clear if the agent that causes the cow version of the disease can infect humans.
The new test does not provide any information about the cause of CJD and it cannot be used to tell if a person will develop CJD in the future.
"Our discovery says nothing of what the causative agent is, nor does it tell us anything more about transmission, or the possibility that these diseases can jump from one species to another," Gibbs said. "What it does is open up a new way of identifying these disorders in humans and animals."
SOURCE: The New England Journal of Medicine (1996;335:924-930)
