Even when using the very best parasite prevention techniques
there are no guarantees of having a completely parasite free puppy.

The following paragraph was taken from the
"Dog Owner's Home
Veterinary Handbook"
written by Delbert G. Carlson, D.V.M. and
James M. Giffin, M.D.

    "Deworming the dam before pregnancy does not prevent
    roundworm infestation of unborn puppies; medications do not
    work on encysted larvae. Accordingly, many puppies are born
    with roundworms."

The most common worms or protozoans found in puppies are:

We do provide our puppies with a well rounded parasite control
program. You will be provided with records of what medications
have been used on your puppy so that your vet will know exactly
what has been done so far.

Even though your puppy has been treated properly it is always a
good idea to assume he or she still has worms. You should take a
small stool sample with you to your first and second vet
appointment so they can check it to for you. A negative stool
sample does NOT mean that your puppy is parasite free. It only
means that the vet did not find any eggs in that particular sample, if
the parasite were not shedding eggs or cysts at that time they will
not be spotted during the exam. If after two stool checks your vet
has found nothing, then you can feel confident that the puppy
worms are no longer a concern.

Signs of parasite problems in a young puppy can include diarrhea,
bloody stool, mucous in the stool, weight loss and poor coat
condition. It would not be uncommon for a puppy to show no signs
of parasites while in our care - and then all of the sudden begin to
have loose stool when they arrive in their new home. Stress can
bring this on. Your new puppy can also have loose stool for the
first few days because of stress only - even in the absence of
parasites. If after your puppy has adjusted to his new environment
and his stool has been firm for several days - and he all of the
sudden begins showing any loose stool or having blood in the stool
etc... you should take another stool sample to the vet for
examination. When dealing with parasites loose stool can be
intermittent or in other cases it could be all the time. Your pup
could also have loose stool if you are feeding him different food, or
with the addition of treats or food scraps that he is not used too.

After your vet is sure that the "Puppy Parasites" are officially
eradicated you can help him to avoid getting worms in the future
by keeping him on one of the monthly heartworm preventatives
that also help deter other common worms.