Eating meat from cattle with Bovine Spongiform Encephalopathy (BSE), also known as Mad Cow Disease, can lead to the development of variant Creutzfled-Jakob Disease (vCJD), an incurable progressive brain disorder. vCJD has killed 200 people in Europe and four in the US, with one as recently as 2012. Thousands of Europeans and perhaps a few Americans are predicted to be vCJD carriers without symptoms, and these people could spread the disease if they donate blood. Developing a test for BSE and vCJD has been a priority for a decade. Now we may have one.
To function normally, proteins in the body must be folded into precise shapes. BSE is a progressive neurological disorder of cattle that is caused when a protein called PrPC becomes misfolded into a form called a prion. Unlike other proteins, this misfolded protein can infect individuals and multiply within the body. Ingestion of meat with prions triggers the misfolding of additional proteins in an individual, and the disease progresses as the abnormal proteins accumulate. The BSE epidemic likely began when cattle were fed meat and bone meal from diseased animals. By 2010 there had been more than 185,000 confirmed BSE cases in just the United Kingdom.
The prion protein is present at low levels in most of the body until the late stages of the disease, making it difficult to detect. One way to address this is to amplify the prions so they can be detected. To develop a test that is sensitive enough to detect prions early, scientists found a way to speed up the conversion of PrPC into prions in the lab. The scientists took samples of normal PrPC proteins with a few prion proteins, and amplified the prions to a detectable level. Their method could amplify as few as 26 prion proteins up to 100 million times in one round, and up to 10 billion times in a second round. Using this approach, the scientists detected prions in animals and in the urine of patients with vCJD.
Using this new test, samples from 14 people with vCJD were all found to be positive while none of the 137 control subject samples were positive. Another group using a similar test identified 18 people with vCJD among 256 samples from France and Britain, two of the countries most affected by BSE. Two of the positive samples were from people who had not yet shown any symptoms, in one case 16 months before a diagnosis of vCJD and in the second case, over 30 months beforehand. The test correctly identified those with the disease and those without it 100 percent of the time.
It is encouraging that there may finally be a test to diagnose vCJD and related diseases at early stages. However, this test must be scrutinized to eliminate the possibility of false positives. In the US, about 6.8 million people volunteer to donate blood every year, and false positive results could affect the blood supply. False positives would also lead to mistaken diagnoses of an incurable and fatal neurological disorder in those people. No one wants that to happen to anyone!