Scrapie transmitted through aerosols

Mice became infected with scrapie when exposed to aerosols containing scrapie-infected tissue, according to recent research results.

An article published Jan. 13 in the journal PLoS Pathogens indicates researchers were able to infect mice with scrapie through an aerosol containing brain tissue. They also showed that as the time mice were exposed to infected tissue was increased, the incubation period for the disease decreased.

A Sept. 2010 report from the Department of Agriculture on the National Scrapie Surveillance Plan states that only sheep and goats are known to become infected with scrapie under natural conditions, but other ruminants, primates, cats, and rodents have been infected under experimental conditions. Most scrapie cases are likely caused by oral exposure, but animals can be infected experimentally through exposure to eyes, broken skin, and mucous membranes, the report states.

Scrapie is a degenerative spongiform encephalopathy believed to be caused by a misfolded infectious protein.

Dr. Lothar Stitz, head of the Institute of Immunology at the Friedrich-Loeffler-Institut in Tubingen, Germany, and one of the researchers on the project, said that, because aerosols have been used for a long time to mimic virus transmission, such as natural influenza virus transmission, the research group hypothesized that prion infections could also occur through the airways. He thinks additional research should consider whether some prions are shed and whether aerosols could contribute to infection, and suggested that the lack of epidemiologic evidence for such transmission may be connected with a lack of investigators considering the possibility.

The article states that aerosols proved to be surprisingly efficient at transmitting prions, and the study results show that such aerosols present an unappreciated risk factor for people working in laboratories and meat processing facilities.

"In light of these findings, it may be appropriate to revise current prion-related biosafety guidelines and health standards in diagnostic and scientific laboratories being potentially confronted with prion infected materials," the article states.

Dr. Justin Greenlee, a veterinary pathologist with the USDA's Agricultural Research Service, said ARS researchers have found that intranasal inoculation has been as effective as intracranial inoculation at causing scrapie, and the recent study results were not surprising. But the recent study appears to be the first in which animals became infected and all other potential transmission sources were eliminated.

Dr. Greenlee noted that researchers involved in the recent study appeared to have had success at effectively generating an aerosol with particle sizes capable of entering the respiratory system and causing direct neural contact via the olfactory epithelium.

The study results do not necessarily appear to be cause for additional concern for laboratory workers, he said, noting that current biosafety protocols call for eliminating aerosol production when possible and using containment and personal protective equipment when aerosols are present. The exposure risk for other locations, such as slaughterhouses, is unknown and dependent on how efficiently the equipment used could generate aerosols of small particle size.

The article is available at www.plospathogens.org.