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Friday, October 26, 2012

Bad news for avoiding prions

Just when you thought prions couldn’t get any scarier, you find out that some birds can pass the infectious proteins intact through their digestive systems. Yes, crows can pick up prions from eating infected meat, and then pass those prions on in their feces. This cheery news is courtesy of Kurt VerCauteren and his colleagues at the United States Department of Agriculture.

Prions are infectious misfolded proteins. Normally, malfunctioning proteins are simply discarded or dismantled, but not so with prions. Upon introduction into a cell, these peptides induce other proteins to misfold as well. In other words, prions are communicable despite having no genetic material. This rampant misfolding results in a number of incurable, deadly neurological diseases known as transmissible spongiform encephalopathies (TSEs). An example would be bovine spongiform encephalopathy, a.k.a. mad cow disease.

Wild animals also succumb to prions and are often scavenged by crows. To test whether prions can be spread by foraging crows, the researchers fed some captured wild American crows the brains of mice infected with prions. The crows’ feces were collected, radiated to kill microbes, diluted, and injected back into mice. 100% of the unfortunate mice treated in this manner came down with TSE. If this doesn’t sound ominous, let me remind you that crows can travel far distances and are indiscriminate poopers.

On the plus side, if you’re not in the habit of ingesting fecal material, you probably don’t have an increased risk of contracting TSE yourself. On the other hand, these data do suggest that it would be nearly impossible to keep prions contained. Short of clearing up every infected carcass before crows or other avian scavengers can get to them, there’s not much we can do.

Kurt C. VerCauteren, John L. Pilon, Paul B. Nash, Gregory E. Phillips, & Justin W. Fischer (2012). Prion Remains Infectious after Passage through Digestive System of American Crows (Corvus brachyrhynchos) PLoS ONE : doi:10.1371/journal.pone.0045774