The “Wired Science” blog at the Wired site has a rather disturbing article about a new study, published by a group of Swiss researchers in the Public Library of Science Pathogens journal [abstract, PDF download available], that appears to establish that prions, the mis-folded proteins that are believed to cause a range of degenerative brain diseases, can infect new animals by airborne transmission. From the authors’ summary:
Prions, which are the cause of fatal neurodegenerative disorders termed transmissible spongiform encephalopathies (TSEs), can be experimentally or naturally transmitted via prion-contaminated food, blood, milk, saliva, feces and urine. Here we demonstrate that prions can be transmitted through aerosols in mice.
The properties of many biological molecules are dependent on their physical shapes. It is quite common to have two “versions” of a compound, mirror images of each other (these are called stereoisomers), where one version is biologically active, and the other essentially inert. As another example, the three simple sugars — glucose, fructose, and galactose — all have the same basic formula, C6H12O6, but differ in the arrangement of those atoms within the molecule.
Prions have the same chemical composition as ordinary proteins, but their shape is different because the molecule is “folded” differently. Unfortunately, this mis-folding transfers itself to normal proteins that are present.
The molecules resemble regular proteins found in the brain cells and other nervous tissues, but their abnormal shape converts healthy proteins into long fibrils that ultimately kill cells.
Like a chain reaction, fibrils create more prions until the host dies from destroyed brain and nervous tissue. All prion infections are 100 percent fatal, and symptoms appear suddenly months or years after infection.
Prions are thought to cause bovine spongiform encephalopathy [BSE, or “mad cow” disease], scrapie in sheep, and variant Creutzfeldt-Jakob Disease [vCJD] in humans.
Given that the incidence of prion diseases in people is quite low, at least in the US, it seems unlikely that airborne transmission is a significant risk to the average person. It’s also important to note that the infectious material used in this experiment was aerosolized brain tissue, not just the sort of droplets that might accompany a sneeze, for example; this is not evidence for transmission of prion diseases as if they were, say, influenza. However, workers in slaughterhouses and meat-processing plants may be more at risk than has been believed before.
Updated Friday, 14 January, 20:17 EST
Jim left an excellent comment below, emphasizing that the transmission mechanism in this experiment is not a plausible one in everyday life. I’ve modified the final paragraph, above, to try to make that clear. In addition, you might want to read his blog post on this same research.