The disease agent in Kuru turns out to be a prion, a malformed version of a naturally occurring protein that catalyses conversion of normal protein molecules into the pathogenic state. It’s a truly weird and scary corner of medical research, because the diseases caused by prions—such as Creutzfeldt-Jakob disease and Fatal Familial Insomnia—kill horribly, first taking the victim’s mind and then their ability to move. Not to mention new variant CJD, also known as Mad Cow Disease.

Now, back to the subject on hand: ritual magicians who perform too many invocations in their head tend to develop a package of symptoms after a while which eerily resembles Kuru. It starts with tremors, unsteady gait, slurred speech, and confusion. Then they become unable to walk, suffer from ataxia and uncontrollable tremors, and show signs of emotional instability. They become depressed, but may suffer from fits of maniacal laughter. In the final stages, they lose all muscular control, can’t sit, or swallow, or speak, become unresponsive to their surroundings . . . and from start to finish it can take between three months and three years.

Krantzberg syndrome is a horrible way to die.

Krantzberg syndrome is probably also the only spongiform encephalopathy that is not a prion disease. (I say “probably” because there are relatively few cases of it in the first place, which makes it very hard to investigate.) However, prion proteins appear to be absent in K syndrome, and extracts from K syndrome brains don’t cause symptoms in other organisms that they’ve been tested on. (For obvious reasons, nobody’s been able to perform the most important test—on other humans.)

The best theory to account for K syndrome is that ritual magic is intentionally designed to attract extradimensional critters—and not just big ones. There seems to be some variety of microscopically small, dumb eaters that materialize inside the gray matter of the practitioner while they are in the process of carrying out some sort of invocation, take a tiny bite, and disappear again. Brain parasites from beyond spacetime, in other words. The brain is a resilient piece of squishware, but if the K-parasites chew enough tiny holes in the headmeat, its owner will eventually succumb to a dementia-like illness. Furthermore, once the eaters have found a tasty lump of brains to chow down on they keep at it. So the disease is progressive, vile, and fatal if unchecked.

Unchecked? Well, yes: we can stop it progressing by putting the victim inside a locked-down protective ward. This is a huge step forward over, say, Kuru or CJD. What’s more, if we isolate the patient for long enough the eaters lose interest and go away; but the victim isn’t going to be casting any spells ever again. (If they’re lucky they’ll still be able to talk coherently and tie their own shoelaces.) It’s a health and safety nightmare.