A while ago, Krispy at A Nudge in the Right Direction asked me a question about picking out a slow disease to attack a character.
One of the diseases I considered were prion diseases. First off, the name "prion" sounds sci-fi, and as you'll see below, they are like no other disease you've ever encountered.
What's a prion? Prions are proteins that are folded in an abnormal state. They have no DNA or RNA, like most living things. They are difficult to destroy and are infectious.
How do they multiply? Prions propagate themselves by causing nearby, normal proteins to fold abnormally like them. Once those proteins misfold, they too cause other nearby normal proteins to misfold, and on and on. (Kind of like the Borg and their assimilation).
How do you destroy prions? With a lot of effort. The normal way we disinfect things to destroy viruses and bacteria often don't work on prions. High, prolonged temperatures, high concentrations of formaldehyde or caustic solutions are needed.
Is it animal, vegetable, mineral, or alien? Prions are not technically alive, in that they do not need food, or respond to their environment. They defy the biological definition that living things have nucleic acids (the building blocks of DNA). However, they replicate. They spread. And their very existence appears to have one effect--to make more of itself. Sounds alien to me.
Where did they come from? Okay, okay. They probably didn't come from another planet. There is a gene in humans on chromosome 20 for a similar prion protein that is a normal protein in humans. Mutations in this gene have cause inherited diseases with prions, like Creutzfeld-Jacob disease (CJD), Gerstmann-Straüssler-Scheinker syndrome, and Familial Fatal Insomnia (Death by Insomnia).
Can human immune systems fight prions? In a word, no.
What other diseases in humans are caused by prions? Mad Cow Disease (or bovine spongiform encephalopathy) has been theorized to have been transmitted to humans and causing variant CJD. Kuru is found in a native population of New Guinea that practiced cannibalism. There are several diseases that affect animals too, such as scrapie and of course, mad cow disease.
Symptoms? All prion diseases are neurodegenerative. They are slow diseases that primarily effect the neural tissues (brain, spinal cord). The symptoms can range from progressive dementia, difficulty walking or standing up, jerking of the limbs and tremors. Familial Fatal Insomnia causes...well. The name says it all.
Is there a cure? No. They are uniformly fatal.
Why aren't we all dead from prions, if they are so hard to kill and there's no cure? When cows are infected, there are low levels of prion in milk and meat, and it's not easy to absorb by eating. You also can't get prions from other people through casual contact. You'd need to be exposed to brain or spinal fluid tissues, or though organ donation.
How common are these diseases? As of 2011, there have been a total of about 211 cases of variant CJD worldwide. As for random, non-inherited, non-Mad-Cow related cases of CJD? 1 in a million cases worldwide, per year. Basically, pretty rare.
Did I just hear a collective sigh of relief?