The Dutch used to lower a raw herring down their gullets on the way to work. Now, I think, the herring have to be frozen. And then thawed - and sold. The reason? (My memory could be shot.) Some worms, found in herring, and thought only to infect fish, were found in seals (i.e., mammals.) I haven't heard of any cases of human infection. (There could be thousands for all I know.) And I know nothing about the efficacy of freezing as a method for killing worms, their eggs, cysts, etc.
I seem to remember a Gunther Grass novel in which Germans played a russian roulette game with steak tartare. The risk: worms infecting the brain of the eater.
I like rare beef, and oysters, and eggnog, and .......
Sometimes I think that the guys at the USDA live on amino acid powders, hydrolyzed with triple-distilled water. And multi-vitamins twice a week.