The health concerns with collecting and keeping wild snails is the unseen possible diseases the snails maybe carrying, and not just may attack other snails (or fish even shrimp) kept in your aquarium but also be a health risk to yourself as well.
As far as know, any wild snail is host to at least one something (fluke, protozoans, bacteria, fungi, virus, worms, even parasitic leeches).. even a healthy wild snail is a carrier. Though not all that it carries will be dangerous at all times unless it dies, gets eaten or produces eggs inside the tank.