What a week for prions
I swear I hadn't intended to do a prion focus this week, but the stories just keep popping up. In this week's Science, Seeger et al. report that prions can be excreted in urine.Prions were originally thought to be confined to the brain, spinal cord, and lymph tissue. Around 2 years ago, researchers had confirmed that they could be detected in muscle tissue as well. Earlier this year, investigators showed that the presence of inflammation in other organs allowed for the infiltration of prions. Infected organs included the liver, pancreas, and kidneys. Following up on those studies in the current report, they've now shown that inflammation of excretory organs can lead to spread of the prion via the urine.
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Obviously, this has big implications in the health care field. Right now, the only way to definitively diagnose a prion disease is at autopsy, by digging into the brain. If this could be detected in the urine or other organs, a definitive diagnosis could then be made prior to death. However, even in those mice who were excreting prion, the concentration was low, and inflammation also had to be present, so we're unlikely to see any diagnostic tests based on this anytime soon. A more immediate implication of their findings relates to work such as this study of chronic wasting disease (CWD), a prion disease of deer and elk. Briefly, the authors gathered mule deer and put them in one of three environments: a pen into which a prion-infected deer was present; a pen in which a ~2-year-old, naturally infected deer carcass was present; or a pen where an infected deer had been present ~2 years prior. (Additionally, they had control deer, which were not exposed to the prion). Their results?
None of the unexposed deer were infected. One or more introduced deer became infected in two of three paddocks containing a naturally infected deer, in two of three paddocks containing a decomposed deer carcass, and in one of three paddocks contaminated with residual deer excreta within 1 year of exposure.It wasn't known exactly how the deer contracted the disease, especially in areas where there had been no infected deer for at least 2 years. This new paper opens up the possibility that they were exposed via an environment contaminated with prion-bearing urine. It remains to be seen whether such a finding will hold outside of the lab, and be replicated in animals that are a better model than mice.
