Protein

Credit to primehealthchannel.com

In all of us, we have proteins. Proteins help form our cell and body structures, they preform vital functions in cells, and they're useful sources of metabolic energy in a pinch. Proteins can also kill you. Prions, also known as Transmissible Spongiform Encephalopathies (TSEs), are neurologic diseases caused by proteins. This might not sound so scary, except that Prion diseases are uniformly fatal in human and animal populations (that we know of today). To phrase that another way, there is no organism that we know of today that has survived an onset of prion disease. There are five known human TSEs, and six animal TSEs (all in mammalian populations) recognized by the CDC.[1] I'm sure there are more in both populations, specifically the animal population, but we just haven't found them yet. In fact, the first people to describe prion diseases were Scottish sheep herders, who observed sheep with Scrapie that would scrape themselves against any available object until their fur, skin, and subcutaneous tissue peeled off.

How do TSEs cause disease? It all starts with a mutation in a gene that codes for a protein, which creates a slightly altered version of the naturally occurring prion. This one altered prion then goes forward, finds other proteins, and re-folds them into more prions like it through a yet undescribed autocatalytic process. Those proteins then go find more proteins, and on, and on. This isn't a very fast process at first- the incubation period of TSEs is somewhere on the order of years, varying a little for each particular prion- but once initial symptoms manifest, the patient presents with a rapidly deteriorating neurological status, going from a functional human being to dead in a matter of about four months for classic Creutzfeldt-Jakob Disease. The protein eventually chews your brain into what actually looks like swiss cheese (see the photo on top). The body mounts no detectable immune response- if I had to venture a guess, it's a combination of the fact that they're very similar to your cellular proteins, and that prion diseases generally don't demonstrate aggressive pathologies outside of the central nervous system (which is devoid of immune cells for good reason). There is no known therapy for prion diseases, and they are capable of crossing species barriers (feline TSEs are believed to be Mad Cow, for example).[3] The only real good news here is that TSEs aren't very easy to transmit, short of a medically transmitted (nosocomial) infection or consuming infected flesh. According to the WHO, the only tissues that demonstrate infectivity are the brain, spinal cord, and eye (these are the most infectious, with corneal transplants causing up to three recognized cases of CJD); As well as the CSF, kidneys, liver, lung, lymph nodes, spleen, and placenta. It's worth noting there are no documented cases of transmission from mother to fetus. [2]

The horror of prions is multifaceted. On one front, they have a higher mortality rate than any other known human pathogen- even Rabies isn't 100% fatal, we're learning. On another, while TSEs aren't readily transmissible, they are extremely hard to destroy. How difficult is it to kill a prion, exactly? The WHO's resource on Prion infection control measures states that Prions are completely unaffected by ionizing and UV radiation, boiling, dry heat less than 300 degrees Celsius (572 F), Formaldehyde, Alcohol, Ammonia, Hydrogen Peroxide, and Hydrochloric Acid. In fact, allowing infected substances to dry or be exposed to alcohol will increase the infectivity of a Prion-exposed material. Even autoclaving at 121 degrees Celsius for 15 minutes is only partially effective. The chemical of choice for cleaning seems to be Sodium Hydroxide. The WHO also recommends the disposal of non-disposable equipment after it is exposed to high and moderate infectious materials of a patient with Prion disease.[2]

Before you let this information really scare you, it's important to realize that you don't have to catch a TSE to develop one. According to the CDC, CJD arises spontaneously in the world population at a rate of about one case per million. In older people, the rate is about 4.6 cases per million. It's believed that the cause is a mutation in the prion genome.[4] Next time you get a headache, it might be worth wondering about.

As always, if you want to do something about Prions and TSEs, support science, and support those in power who support science. Share what you've learned here, do your own research, and feel free to share any questions, comments, or concerns with me.




[1]http://www.cdc.gov/ncidod/dvrd/prions/index.htm
[2]http://www.who.int/csr/resources/publications/bse/whocdscsraph2003.pdf?ua=1 (section 6)
[3]http://www.cdc.gov/ncidod/dvrd/prions/resources/BelayE_Annu_Rev_Microbio.pdf (page 284)
[4]http://www.cdc.gov/ncidod/dvrd/cjd/