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

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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

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  1. 1. enternewid 2:59 pm 01/14/2011

    The US and Canada and the Cattle associations are covering up any new cases in the US.

    Link to this
  2. 2. AbnormalFacies 3:14 pm 01/14/2011

    The study’s findings may indeed have consequences for laboratory guidelines, and even slaughtering/handling guidelines, but to interpret them as demonstrating the reality of contracting a prion disease by airborne transmission is, IMHO, incorrect.

    There’s zero evidence for direct contact or airborne transmission of prion diseases, and simply because mice were infected with aerosolized brain tissue homogenates does not mean there exists the potential for inoculation via air under normal circumstances.

    Link to this
  3. 3. joshbw 3:30 pm 01/14/2011

    And what evidence do you have to make that assertion? It is one thing to say that it would make business sense for the cattle industry to avoid reporting such a thing because of concerns over market backlash, but it is quite another to definitively assert a collaborative attempt among many parties to suppress information. The first is an observation based on general business motive, the other is an unsupported conspiracy theory

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  4. 4. Wayne Williamson 1:36 pm 01/15/2011

    Sounds like another bio weapon has been born…hopefully someone is working on a vaccine….

    Link to this
  5. 5. E-boy 9:55 pm 01/16/2011

    And your evidence for this is? Just for the record there are instances of tissue aerosolization in agricultural situations causing outbreaks of Hanta virus. It’s a rarity, to say the least, but it’s possible. Nowhere in the article did it say Prions had become an airborne scourge, only that the possibility of transmission through inhaling prion particles existed. Which they demonstrated. Perhaps you thought they said that, but they didn’t.

    As for the first poster’s comment about cover ups, I very much doubt cover ups are occuring. The amount of beef that gets eaten in this country means that by now there’d be cases of spongiform encephalitis all over the place if contaminated meat were making it to the plate. There aren’t. Extroadinary claims require extroadinary proof.

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