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Part of the reason why that 'medieval disease' was able to spread back then was because of a noticeable lack of cats that would've treated the rat/mouse population like an all you can eat buffet. . .and that lack of cats was caused by fools(replacing God's knowledge/wisdom with their own), cowards(for not standing up to the rot and corruption that infected almost every institution including churches), and the superstitious(thinking cats are from satan while also believing God can't handle any and every evil, disease, or whatever nastiness that thrown everyone's way.)
So here we are in the 21st century and everyone is supposed to know better. . .and yet. . .AND YET. . .it may look it we are about to get a sequel of the first time around. . .all because of fools, cowards, and the superstitious.