Improper food prep.
Anyone can be a host.. especially when you're consuming microscopic ova. You have no idea if you cant see it.
I think anasakis may have visible ova.. or something that provides a clue. Chefs are supposed to be trained to identify and remove anasakis from fish.
In the US, its a law that any kind of sushi or fish used for sushi needs to be frozen prior to being sold. Not sure if that applies to just supermarkets or restaurants too.
I'll never eat it again unless it's the pre frozen and cooked california roll.
Its a shame too... i loved sushi