Prions, the agents that cause bovine spongiform encephalopathy (BSE or mad cow disease) and Creutzfeldt-Jakob disease, can spread through the air and induce infection, according to new research led by the University of Zurich; a discovery that may come as a great surprise to many, because until now it was thought airborne prions were harmless.

Because of their findings, the researchers recommend that science labs, slaughterhouses and animal feed plants change their safety procedures to include precautionary measures against the possible airborne transmission of prions.

You can read how researchers at the University of Zurich and the University Hospital Zurich in Switzerland, plus the University of Tübingen in Germany, made their discovery in the 13 January issue of PLoS Pathogens.

We already know that prions can be passed on through contaminated surgical instruments, and more rarely, through blood transfusions, but until this study, it was thought prions were not capable of being airborne like viruses, for instance flu and chickenpox, which are transmitted this way.

For their study, senior investigator Dr Adriano Aguzzi, a professor at the Institute of Neuropathology at the University of Zurich, and colleagues, put mice in special inhalation chambers and exposed them to aerosols containing prions.

They were very surprised to find that inhaling the prion-tainted aerosols induced disease (in this case scrapie) with frightening efficiency: just one minute of exposure infected 100 per cent of the mice, said Aguzzi in a press statement.

Also, the longer the mice were exposed to the prion-contaminated aerosols, the shorter the disease incubation period and the more quickly the symptoms of a prion disease appeared.

They also found the same occurred in mice lacking various immune cells (such as B- and T-cells) and immune functions, leading them to conclude that “a functionally intact immune system is not strictly needed for aerogenic prion infection”.

Aguzzi told the press these findings come as a great surprise and contradict the widely held view that prions are not airborne.

The prion disease BSE that caused the mad cow disease epidemic has led to the death of hundreds of thousands of cows in the past decades.

A prion is a protein that is not folded in the way required for normal functioning, and when it comes into contact with other proteins it acts as a template and causes them to misfold as well, eventually causing a chain reaction that destroys cells.

When humans ingest food made from cows infected with BSE, the prions they ingest can cause variant Creutzfeldt-Jakob disease (vCJD), a rare and fatal neurodegenerative condition where the prion chain reaction causes brain cells to die and the affected brain tissue takes on a characteristic spongy form. So far 300 people have died from catching vCJD this way.

Places like science labs, slaughterhouses and animal feed plants tend to have stringent regulations to prevent prion transmission, but these generally do not include procedures for preventing airborne transmission because it was assumed prions don’t travel that way.

Aguzzi and colleagues suggest this should now be changed in order to minimize infection in humans and animals. They stressed however that these findings came from producing aerosols containing prions under lab conditions and there is no suggestion that people with Creutzfeldt-Jakob disease exhale prions.

“Aerosols Transmit Prions to Immunocompetent and Immunodeficient Mice.”
Johannes Haybaeck, Mathias Heikenwalder, Britta Klevenz, Petra Schwarz, Ilan Margalith, Claire Bridel, Kirsten Mertz, Elizabeta Zirdum, Benjamin Petsch, Thomas J Fuchs, Lothar Stitz, Adriano Aguzzi.
PLoS Pathogens, 7(1): e1001257, published online 13 Jan 2011

Additional source: University of Zurich (press release, 13 Jan 2011).

Written by: Catharine Paddock, PhD