Prion Test Would Allow Early Detection of Mad Cow, Other TSEs

WOOSTER, Ohio -- Ohio State University researcher Srinand Sreevatsan not only believes early detection is the best way to fight mad cow disease. He’s also creating tools to make it possible. “There is a desperate need for a fast and reliable test for the diagnosis of transmissible spongiform encephalopathies (TSEs) in live animals,” said Sreevatsan, a scientist with the Food Animal Health Research Program (FAHRP) on the Ohio Agricultural Research and Development Center’s (OARDC) Wooster campus. “Early detection could lead to efficient surveillance systems that may avert or control this group of diseases.” Funded by a three-year U.S. Department of Defense grant, Sreevatsan is developing a test to detect prions -- the agents responsible for bovine spongiform encephalopathy (BSE, commonly known as mad cow disease) and other TSEs such as scrapie in sheep and goats, chronic wasting disease (CWD) in deer and elk, and Creutzfeldt-Jakob disease (CJD) in humans. Currently, definite diagnosis of TSEs is only possible after death, which limits surveillance efforts and leaves farmers fighting a hidden enemy. In the case of mad cow disease, it takes anywhere from two to eight years for a cow to show symptoms of infection. Sreevatsan’s lab is looking for a way to identify prions through clinical samples such as blood, serum or lymphoid tissues before the onset of symptoms. The abnormal form (PrPsc) of a normal host protein (PrP), prions are found mainly in the brains and spinal cords of infected animals and humans.  “The idea is to detect the prion protein, which is folded abnormally as compared to its normal counterpart, in an animal that’s still living, using non-invasive approaches,” Sreevatsan explained. “Identifying infected animals early on will be profitable for the farmers, and it will also be very useful in getting rid of infected animals. Anything that will help both the farmers and public health in general, by preventing a spillover of potentially infected meat or meat products into the food chain, will benefit the animal industry a lot.” To develop his test, Sreevatsan is using scrapie as a model, since the disease is present in Ohio. And unlike other researchers working on the development of prion-detection tests, he’s using high-affinity nucleic acid ligands -- molecules that have shown the ability to bind to and differentiate between different proteins -- instead of antibodies. “Most people use antibodies, but antibodies so far have not shown promise toward differentiating different isoforms of the prion protein,” Sreevatsan said. “If an antibody has been generated that binds to an abnormal isoform, it’s been shown that it also binds to the normal isoform of the protein. We are working with the fact that nucleic acids bend in different confirmations, and this differential in bending offers differential in binding capacities of the nucleic acids to different proteins. That way, they may be able to differentiate confirmations of the different (prion) proteins.” Working with nucleic acid ligands offers additional advantages, Sreevatsan explained. “We are able to generate ligands in the laboratory without the use of lab animals and fairly inexpensively. Most of the tagging for the detection techniques is done in vitro, which is not as complicated as it would be for tagging other macromolecules. So, once the ligands are identified, it would be a fairly simple process to develop a diagnostic test.” The test-development process involves finding ligand candidates, defining the physical and chemical characteristics of the binding, and determining whether this binding is optimal for detecting very low quantities of the prion protein. That’s key to developing a test reliable enough to allow health and agriculture authorities to adequately survey for TSEs, keep the meat supply safe and prevent disease in humans. OARDC is the research arm of Ohio State’s College of Food, Agricultural, and Environmental Sciences. Editor: Photographs for this article are available. Contact Ken Chamberlain, (330) 263-3779, chamberlain.1@osu.edu.