I have been using Bob Martin tablets to worm DCat for the past year or two, but thanks to the Litter Tray I have learnt that these aren't very effective. However, my vet won't prescribe a veterinary-grade wormer without seeing DCat first to do a "parasite screen". What does this involve and is it really necessary? Should I just buy Drontal from PetsAtHome? DCat hates going to the vet so I'm reluctant to subject him to a parasite screen if there is no real need to have one.