The 'Leucochloridium paradoxum' (LP) pathology is even weirder than the aricle states. I understand that LP will not survive an adult bird's stomach acid, so the bird cannot eat the LP it plucks from the snail.

The bird must feed LP to its chicks which have much weaker digestive juices, where it will continue to live and spawn in the birds intestinal track.

Rinse - Lather - Repeat.