I'm not sure what young rat lungworms look like, but don't apple snails have a chance to ccarry them? some of the google picks make it look black? maybe that's the issue?
I just glanced at the website linked and they mentioned worms so...~shrugs~. Best of luck though.
-duckweed- -black and white marble, anything but VT-
-javamoss- -koi marble, anything but VT)
-hatchable brine shrimp eggs-
-indian almond leaves-
-Melano Halfmoon male-
-steel blue or royal blue CT or HM female-