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Bad prion breath: Mad cow disease agent can infect via the air


As if it weren't bad enough that deadly prions can survive boiling and radiation, now comes word that aerosolized forms of the pathogen can enter the nose and find their way to the brain, with fatal consequences.


Prions, you may recall, were the reason you avoided beef in Europe in the 1990s. They triggered the infamous mad cow disease epidemic in the U.K., which spread to the rest of Europe and other parts of the world.


Prions are proteins that all animals produce, but sometimes, toxic mutant versions are made. These malformed versions can cause normal prions to become pathogenic, setting off a chain-reaction conversion to the deadly kind. The bad prions destroy neural tissue, sometimes leaving the brain full of holes like a sponge (hence the formal name, "spongiform encephalopathies," for these diseases).


Transmission of the disease from one host to another generally came about through ingestion. Cows passed on the disease because of forced cannibalism: in the U.K. in particular, farmers turned the parts of cows not fit for human consumption into feed for other cows. Humans contracted the disease probably by eating ground beef and sausage, which are more likely to contain the nervous system tissue where prions mostly lurk. (I wrote a book about prions in 2003 titled "The Pathological Protein," although I wish I had thought to title it "Cannibalism's Revenge.")


Now, it seems as if you can get a prion disease through inhalation, at least if you're a mouse. In Adrian Aguzzi's lab at the University Hospital Zurich, mice could get sick after just one minute of exposure to spray-bottle prions. How long it took for the mice to sicken depended on how much they inhaled. The journal PLoS Pathogens published the work on January 13.


Besides adding a new dimension to prion personality, the results really apply to those who work with prions in the lab. As Aguzzi and his team write, "This previously unappreciated risk for airborne prion transmission may warrant re-thinking on prion biosafety guidelines in research and diagnostic laboratories." So, hold your breath!


In the case of your cheeseburger, changes in farming practices starting in the 1990s have brought mad cow disease under control. According to statistics from the World Organization for Animal Health, the U.K. saw seven mad cows in 2010--a far cry from its peak year of 1992, when it found 37,000 cases and slaughtered hundreds of thousands as a preemptive measure. The rest of the world reported fewer than a dozen last year. (The U.S. reported its only two cases in 2004 and 2005.)


And don't worry if you were avoiding eating beef at the height of the mad cow epidemic but enjoyed a few whiffs of the char-broiled aroma. You did not inhale prions. If you did, you wouldn't be around to read this post.

Image of brain slice showing mad cow-produced holes (white areas) from a human victim courtesy of CDC/Teresa Hammett

The views expressed are those of the author and are not necessarily those of Scientific American.

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