An article in the September issue of Nature Medicine describes the success of neuroscientists at the University of Texas Medical Branch in designing a blood test that can, for the first time ever, detect mad cow disease in blood samples of living animals. The most immediate uses for the test may be found in screening for the human form of the disease, known as variant Creutzfeldt-Jakob disease (vCJD), in human blood banked for use in transfusions and donated organs intended for transplant, and screening animals in the human food chain, particularly cattle.

The technology itself is a remarkable achievement. Very few of the malfunctioning proteins that trigger the destruction in the brain pass through the blood-brain barrier; the amounts are so small that conventional methods fail to detect them. Currently, the only way to detect vCJD and mad cow disease, or bovine spongiform encephalopathy (BSE), is by examining brain tissue of the infected person or animal after death. Both diseases are incurable and fatal.

Several years ago, the scientists at the University of Texas Medical Branch made the fundamental technological breakthrough, developing a technique called protein misfolding cyclic amplification (PMCA). The test detects incorrectly shaped (misfolded) prion proteins. Over the last four years, the scientists have improved and automated the test. Their refined technique combines several biochemical cycles of amplification and a boost of sound waves, causing the proteins multiply 10 million-fold, until they are finally detectable in a blood sample.

For the researchers, the next step is detecting these proteins in the blood of animals before the animals develop clinical symptoms, and then applying the technology to human blood samples. BSE and vCJD may incubate quietly for decades before symptoms appear. During that time, BSE may spread and enter the human food chain, potentially infecting large numbers of people with vCJD. For this reason, development of a test to identify the disease in human blood achieves a compelling public health goal. Until a treatment for vCJD is found, however, the test will be of limited use in the health care of those infected with the disease.

The number of people and animals that are carriers of vCJD and mad cow disease, respectively, is unknown. Since the UK epidemic of bovine spongiform encephalopathy in the 1980s, Britons and their European neighbors have guessed that potentially millions of people were exposed. In the US, two cases of BSE in cows have been identified; worldwide so far, 180 people have died of the human variant.

Public health experts and pharmaceutical companies are interested in quantifying the problem. In other words, it would be useful to know how many people are currently infected with vCJD, but do not know it and how many cattle have BSE. Pharmaceutical companies are more likely to spend money developing treatment if the numbers show that a significant number of cases are on the horizon. Researchers may one day find a benefit to early diagnosis of prion diseases, perhaps in limiting transmission to others, and there is hope that treatment strategies could be developed before a large outbreak or epidemic.

Blood test for prion diseases reported. Center for Infectious Disease Research and Policy, University of Minnesota. Available on the Internet at http://www.cidrap.umn.edu/cidrap/content/other/bse/news/aug2905bse.html. Accessed 30 Aug 2005.

‘Mad cow’ proteins successfully detected in blood (press release). University of Texas Medical Branch. 28 Aug 2005. Available on the Internet at http://www.eurekalert.org/pub_releases/2005-08/uotm-cp082505.php. Accessed 30 Aug 2005.