When it comes to the safety of our food supply, prions have a bad reputation, and understandably so. Prion diseases, or transmissible spongiform encephalopathies (TSEs), are a family of rare, progressive neuro-degenerative disorders that affect both humans and animals.1 They are distinguished by long incubation periods, characteristic “sponge-like” appearance of infected neuronal tissue, and a failure to induce an inflammatory response by the host.2 Prions were initially discovered as deleterious proteins that somehow alter their shapes to become infectious, causing normal, non-infectious prion proteins to change their shape and aggregate to create fatal neuro-degenerative diseases. Until recently, the normal function of non-infectious prion proteins was unknown. But scientists now believe normal, non-infectious prion protein function helps to maintain the myelin sheath that insulates and protects electrical signals transmitted by our axons.3 See Figure 1 for a 3-dimentional representation of a prion. All of this being said, what impact do infectious prions have on the food supply, and how are consumers being protected from consuming prion-contaminated foods?
Figure 1: 3-dimensional structures of a typical prion. A space-filling model (left) and the secondary structures (right) are shown.
How Do People Contract TSE?
It is theorized that consumers may contract a version of bovine spongiform encephalopathy (or BSE, otherwise known as Mad Cow Disease) from eating contaminated meat. The most well-documented cases of meat contamination are thought to be connected to BSE. The incubation period of BSE is usually four to six years, during which the cow may show symptoms such as a lack of coordination, or it may act very nervous or violent. Once a cow shows symptoms, it becomes progressively sicker until it dies. The human version of the prion disease, variant Creutzfeldt-Jakob disease (vCJD), is rare.1,4,5 The disease causes progressive loss of brain function, and affected individuals usually die within a year of the start of symptoms. As of June 2008, 208 people globally were thought to have contracted vCJD from eating food made from cows that had BSE.6
The National Institutes of Health report that, despite a strong similarity between prions that cause BSE and vCJD in laboratory tests, there is no direct proof to support the theory that BSE can cause vCJD.5 However, at this time, there is no treatment or vaccine for BSE and there are no reliable ways to detect the prion disease in a living cow.4,5,6,7 Therefore, regulatory agencies have taken an aggressive approach to prevent the spread of BSE and to ensure that infected animals do not enter the human food supply.
How Are We Protected?
Our first and best lines of defense against potentially contracting TSEs from food are the combined efforts of our administrative agencies. The FDA, USDA, EU commission and other in-country agencies work together to ensure that high risk cow parts are not used to make any animal feed, including pet food, that could be a potential vector for BSE. Other efforts include the prevention of high-risk cow products from entering the food chain via importation. In addition, high-risk cow parts, such as brain and spinal cord tissue, are regulated and are not used to make food for human consumption.5,6
The Future of Prion Detection
The future is looking bright for the rapid detection of infectious prion proteins in live cows. With funding from USDA’s Cooperative State Research, Education, and Extension Service (CSREES) National Research Initiative (NRI), scientists in New York created a new device that may provide a faster, easier and more reliable way to test for BSE. This research, conducted at Cornell University, has led to the development of nanoscale resonators, which are tiny devices that function like tuning forks by changing pitch with increased mass. In experimental trials, the sensor detected infectious prion proteins at concentrations as low as 2 ng/ml, which is the smallest measured level to date. Currently, these nanoresonators only detect prions in saline solution, but efforts are underway to detect prions in more complex solutions such as blood.7 As more information and technology become available for prion detection, it is not hard to imagine a rapid test being developed for food products as an added measure to the controls that our administrative agencies have put into place.
- World Health Organization. (2014) “Prion Diseases,” available at http://www.who.int/zoonoses/diseases/prion_diseases/en.
- Centers for Disease Control and Prevention. (2012) “Prion Diseases,” available at http://www.cdc.gov/ncidod/dvrd/prions.
- Talan, J. (2010) “Possible Role for Normal Prion Protein Identified in New Study: To Maintain Myelin that Insulates the Axon,” Neurology Today, 10(10) (pp. 8–9), available at http://journals.lww.com/neurotodayonline/Fulltext/2010/05200/Possible_Role_for_Normal_Prion_Protein_Identified.6.aspx.
- National Health Service. (2013) “Creutzfeldt-Jakob Disease,” available at http://www.nhs.uk/conditions/creutzfeldt-jakob-disease/Pages/Introduction.aspx.
- National Institute of Neurological Disorders and Stroke (NINDS). (2014) “Creutzfeldt-Jakob Disease Fact Sheet,” available at http://www.ninds.nih.gov/disorders/cjd/detail_cjd.htm.
- U.S. Food and Drug Administration. (2012) “Animal and Veterinary: All About BSE,” available at http://www.fda.gov/animalveterinary/resourcesforyou/animalhealthliteracy/ucm136222.htm.
- Kish, S. (2008) “Nanotechnology Improves Food Safety by Detecting Prions,” available at http://www.csrees.usda.gov/newsroom/impact/2008/nri/10091_prions.html.