Each family makes different versions of pierogi, even ruskie are different between the families. I (predictably) prefer the version that my mother makes, which has extra thin dough and slightly higher cheese to potato ratio, but all of them are good.
Other than ruskie I love pierogi z jagodami (with wild blueberries). They are the best summer food.
A parasite specialist quoted in the paper said that these eggs are so resilient they can survive boiling water or being baked in an owen. The parasite itself is a nasty one (e.g. will eat out your eye from inside if it lodges there). This convinced me to drop wild blueberry dishes I didn't prepare myself.
You can also get slightly different version of bąblowiec from dogs, and dogs touch EVERYTHING when they go on a walk, so basically if you're afraid about that you should deparasitize (is that a word in English?) the dog every year if you take your dogs for walks in nature (or visit places where lots of dogs poop - like dog parks).
In the end it's not that common (I mean it's common among foxes but not common among people - there's like few dozen cases a year in Poland AFAIR). Probably many more causes are never recognized because it develops very slowly but still - if it was easy to catch people would talk about it constantly.
Pierogi Ruskie is my #1 food when going back. That cheese filling with onion + a good dollop of sour cream. They are the best pierogi for me.