Zombie Deer Disease and Prion Evolution

Chronic Wasting Disease has been spreading rapidly among deer in the central states. The disease is caused by prions, misfolded proteins which characterize several fatal neurodegenerative disorders: most infamously Mad Cow Disease, but also Scrapie, Kuru, and Creutzfeld-Jacob disease. The way prions cause disease is that a single misfolded prion protein coming into contact with correctly folded proteins in the body exerts a sort of "peer pressure" on other proteins, causing them to also become misfolded in the same manner. Through this, the number of misfolded proteins grows exponentially over time. Prions contain no genetic material, and unlike viruses, are firmly in the realm of things that are "not alive." Despite this, prions can be infectious, passing from host to host to cause disease, and interestingly, still experience a form of evolution.

This ability to evolve is part of the growing concern over the spread of chronic wasting disease. Not only does this disease cause major dispruptions to ecosystems by disrupting natural species' equilibrium and killing many deer, the disease may eventually evolve to spread to humans. Thus far, research has shown both experientially, and in the laboratory that humans are not susceptibe to Chronic Wasting Disease. In 2005, a study followed 200 individuals who had eaten deer meat with detectable levels of prion for 6 years. None showed any symptoms of the disease during that time-- the only difference between this group and the general population was that most stopped eating venison after the whole ordeal. Furthermore, laboratory experiments with humanized mice have shown that humans are not susceptible to CWD prions. However, laboratory research has uncovered two worrying facts: squirrel monkeys, which are relatively much more evolutionarily related to humans, are susceptible to CWD. Second, CWD prions can evolve in laboratory settings such that they are infectious to human proteins. If this happened in nature, a second epidemic of zoonotic prion disease could be on our hands. In the mean time, perhaps knowledge of the past Mad Cow disease outbreak, news coverage spreading awareness, and caution may help reduce the impact of an outbreak should it occur.

~Lisa Manzanete

References:
https://www.ncbi.nlm.nih.gov/pubmed/25225155
https://www.cdc.gov/prions/cwd/index.html
https://www.cste2.org/Webinars/files/CWD_Slides_FINAL.pdf
http://news.bbc.co.uk/2/hi/health/8435320.stm