I would get them a little quarantine tank for now, i will try and find some info for you.
Not the writer o0f this information below.
Parasites
There are several parasites that have snails as an intermediate host. However, apple snails are relatively resistant to many of these parasites, which are often host specific and do not regenerate in other hosts like apple snails.
However, at least one parasite (Angiostrongylus cantonensis, a nematode, also know as the rat lungworm), uses the apple snail as an intermediate host. This parasite has the rat as its main host, but humans can be infected when raw snails are consumed. In rare cases this infection can cause eosinophilic meningonencephalitis resulting in severe neurological disorders and even death.
But don't worry if you got your snail from a pet shop, the only way the snail can be infected is by living in water were infected rodents (rats or mice) live. And even then, you have to drink the water or eat the snail or your water-plants (on which the parasites attach themselves after finishing their life cycle in the snails and wait there for being eaten by their main-host).
If you suspect your snail from being infected, just keep them away from their main host. This breaks the life cycle of the parasite, and you will get lost of them. Beware that it can take a long time, because many parasites are able to have several generations in their intermediate host. Better thing to do is waiting until the snail has laid their eggs and go on with the young, uninfected snails.
More detailed info on Angiostrongylus cantonensis can be found at:
http
/www.cdfound.to.it/HTML/ang.HTM.