Check if they have fleas as they can get worms via the fleas, I know it sounds incredible but the fleas carry them because of the wild animals they bite and drink from.
Fleas can be part of the life cycle of tapeworm, but not roundworm as far as I know, which is what eclare's dog has.
As already said, worm treatments treat any worms that the dog has at that time, but the dog can be infected again the next day, week, month or never.
I sometimes send samples off and have a wormcount done. If no worms are present I don't treat, but if they are I use Milbemax.