Wow, what a hideous idea.
There are lots of unmentioned questions regarding your scenario: the main being transmission.
So, I'm guessing you aren't talking about eating brains as a means of transmission - a Kuru epidemic would require a change in diet, unless it's a sequel to Soylent Green.
So maybe it's airborne or, like covid, transmitted via droplets or, like ebola, via blood.
Like other prions, it's 'simple' – it folds similar proteins on contact.
Most proteins are buried behind all sorts of defences. But let's say there's a keratin prion - it converts keratin into itself, which happens to convert hair into a gaseous particulate - like smoke - which is highly carcinogenic.
So in this scenario, infected hair would - at first slowly, and then more rapidly, collapse, leaving behind an airborne residue of prions. There's your pandemic.
Prions resist degradation and persist in the environment for years.
FFP3 respirators may offer some protection. Not much, mind you.
So what could civilization do to deal with it?
Let me hazard a guess: We adapt or we die.
Much of what happens depends upon if there's any natural resistance to the cancer already. Let's assume not: It's like being resistant to any other toxic carcinogen - not likely.
Maybe there's some sort of preventative k-prion spray that dissolves it. Well, the outside is a huge place, and the spray is more likely to do damage itself than to help out.
I reckon we would die. What civilisation would need to to is to accept it's end, and mourn with grace and dignity.