I wouldnt describe them as parasites, however they can be a problem if not looked after properly.
Firstly, you may end up with 100+ baby snails. Decide what you are gonna do with them all. They take a while to grow too.
Second, whilst growing, they will need calcium for their shells. Do you have hard water? This will help, however you may still need to add a calcium suppliment as there might not be enough in your water. If there's a calcium deficiency, their shells wont form properly, they'll get pitted and not look as good.
third, they will require food. Algae wafers, vegetables etc. However with so many small snails in the tank it will take time for them to reach the food, in which time most of the fish will have eaten the food (that's if you dont use a separate tank to raise them). Apple snails will eat plants if not fed enough, so be aware of that.
Fouth, apple snails can be quite messy, so with loads of babies expect more waste on the bottom. keep an eye on your ammonia levels.
lastly, the eggs need to be kept moist, but not damp. They shouldnt dry out on the inside, doesnt matter so much about the outside. They can get moisture if the hood is wet inside from condensation etc.
check
www.applesnail.net there might be some info on there
Good luck!