Aerosolized Prions Efficiently Transmit Scrapie (and Presumably other Spongiform Encephalopathies Like Mad Cow Disease) in Mice — a New Finding and Possible Warning for Researchers and Slaughterhouse Workers

© 2011 Peter Free

 

14 January 2011

 

 

After Europe’s “mad cow” scare more than a decade ago, this discovery will draw some attention

 

Researchers have discovered that aerosolizing scrapie prion-infected brain tissue and exposing mice to the contaminated air for relatively short periods is enough to infect them with the fatal disease.

 

Given that prions from different diseases appear to operate similarly, the finding has potentially worrisome implications for other transmissible spongiform encephalopathies including mad cow disease (bovine spongiform encephalopathy) and chronic wasting disease (in deer, elk/wapiti, moose).

 

For people who remember mad cow disease, the fear factor outside agriculture came from its oral transmission to human beings (through eating beef products) as “variant” Creutzfeldt-Jakob disease (vCJD or, sometimes, “new” vCJD).

 

 

Background

 

I wrote about prions and spongiform encephalopathies in the context of Mad Cow Disease (Bovine Spongiform Encephalopathy) and its human analogue, variant Creutzfeldt-Jakob disease, in 2001.

 

At that time, no one was particularly concerned that prions might be capable of infecting people and animals via contaminated air.  Nor did anyone seem to suspect that prion disease could take hold in the absence of mediation by the host’s immune system.

 

 

Quoting from the January 2011 research paper

 

Johannes Haybaeck et al. said:

 

[P]rions are not generally considered to be airborne.

 

Here we report that inbred and crossbred wild-type mice, as well as tga20 transgenic mice overexpressing PrPC, efficiently develop scrapie upon exposure to aerosolized prions. NSE-PrP transgenic mice, which express PrPC selectively in neurons, were also susceptible to airborne prions.

 

Aerogenic infection occurred also in mice lacking B- and T-lymphocytes, NK-cells, follicular dendritic cells or complement components.

 

Brains of diseased mice contained PrPSc and transmitted scrapie when inoculated into further mice.

 

We conclude that aerogenic exposure to prions is very efficacious and can lead to direct invasion of neural pathways without an obligatory replicative phase in lymphoid organs.

 

This novel pathway of prion transmission is not only conceptually relevant for the field of prion research, but also highlights a hitherto unappreciated risk factor for laboratory personnel and personnel of the meat processing industry. . . .

 

While we did not investigate whether production of prion aerosols in nature suffices to cause horizontal prion transmission, the finding of prions in biological fluids such as saliva, urine and blood suggests that it may be worth testing this possibility in future studies.

 

© 2011 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, Aerosols Transmit Prions in Immunocompetent and Immunodeficient Mice, Public Library of Science Pathogens [PLoS Pathogens] 7(1), doi: 10.1371/journal.ppat.1001257 (13 January 2011) (from abstract and the paper’s concluding discussion) (paragraphs split)

 

 

Very nicely done research

 

The team touched the bases relevant to their immediate question.  The use of genetically altered mice was clever.

 

Statistically speaking, I suppose one could attack the apparently small sample sizes used for each sub-question.  But given the epidemiology of transmissible spongiform encephalopathies, combined with the pathological evidence the team uncovered, I doubt there are reasonable grounds to immediately doubt the aerogenic causation finding.

 

 

Disease risk to the public should be vanishingly low

 

Homogenizing neural tissue from a diseased animal directly into a person’s airstream is not likely to happen except under research or slaughterhouse conditions.

 

But — were I hunting deer, elk, or moose in chronic wasting disease country, I probably would not shoot one in the head, while standing only centimeters away.  Vanishing risk does not mean no risk.  The Chronic Wasting Disease Alliance has useful (pre-aerogenic risk) guidelines posted.