04.02.2011

Aerosols transmit infectious prions to mice

Prions, the pathogenic agents that cause transmissible spongiform encephalopathies such as BSE and scrapie, can be passed on through contaminated food and bodily fluids, but are not generally considered to be airborne pathogens. However, a new study suggests that airborne prions are far from innocuous, and that inhalation may be a highly efficient route of infection.

The authors, from the University of Zurich and the Friedrich Loeffler Institute Tübingen, say it may be advisable to re-think biosafety guidelines in research and diagnostic laboratories, as well as in abattoirs and animal feed factories, in light of their findings.

The researchers housed immunodeficient and normal mice in inhalation chambers where they were exposed to aerosols containing prions at various concentrations. All but the very lowest levels of prions (0.1%) were found to cause disease. Exposure to the highest levels of prions (20%) for one minute was sufficient to induce disease in all of the mice, and longer exposures resulted in shorter incubation times. The prions appeared to move from the airways and colonize the brain directly, as mice with various defects of the immune system – which previous research has shown to prevent the passage of prions from the gut to the brain – were not protected from infection.

Professor Adriano Aguzzi, who led the study, said the findings were “entirely unexpected” and appear to contradict the widely held view that prions are not airborne. Although people and animals are unlikely to encounter airborne prions, since infected patients do not exhale them, aerosols containing the proteins could be created artificially in some circumstances – for example in laboratories or when animal carcasses are processed. The precautionary measures employed in these situations do not usually include protection against aerosols, but Professor Aguzzi suggests it may be advisable to reconsider the regulations given the possibility of airborne transmission of prions.

The study is published in the open-access journal PLoS Pathogens and is available online at http://dx.plos.org/10.1371/journal.ppat.1001257.