I just picked up a pup the other day and was told he had an averse reaction to the vaccination I asked he be given before being sent to me. Stools were loose (but okay when I picked him up), he's thin, coat looks a bit dry especially on the sides of his body, and while he's eating, his appetite is less than stellar. I was assured he'd been dewormed.
Stool check. Round worm.
He's got a lot of energy, so it's not too bad, but a serious infestation can be very dangerous.