TBH, if you see your dogs has played, chewed or been around slugs & snails, you have an advantage over those of us who don't -just their slippery trail of where they have been, can be enough to transmit lungworm but if you see the blighters you are alerted to the danger sooner. Due to Purdey having lungworm a few years ago I treat for it, as I know it is in our area but I never really see her (or the other 2) bothering with them at all, so Lungworm can be quite a 'hidden' danger.
Good idea to mention it to your vet, as he will have info on whether it is a problem in your area yet & the correct preventative treatment (Advocate is the only licenced preventative treatment for lungworm but some vets are still advising Milbemax)
lindsey x