blood mucous in 4 month old puppy shitzu

Question
I just noticed today that my shitzu 4 month puppy had blood and mucous,slimmy substance in stool.
I took him to the vet two weeks ago when i purchased him from Puppy Palace and supposedly he had been dewormed, so i don't know what it can be.  Also has very wet stool, not hard and i've changed food but to no avail. Please advise what the blood in stool and mucous means.

Answer
There are several intestinal parasites that your puppy could have which are causing this problem. The routine dewormer that your vet or the pet store used does not cover all parasites. Your pup may have Giardia,(also contagious to you so wash your hands frequently after handling the puppy until this has been ruled out), coccidia and whip worms. I would advise you to bring a stool sample to your vet and ask them to send it out to a lab rather than run it in house. There are very sensitive tests available at the major veterinary diagnostic labs now for detecting parasites which are far more sensitive than the standard fecal flotation test that we used to perform in the hospital. Once the puppies parasites are identified they are usually easy to treat. The exception to this is Giardia. Unfortunately, we are diagnosing Giardia that is very resistant to the medications which have been effective against this protozoal parasite in the past. Many of the puppies purchased at pet stores, who originate from puppy mills, seem to have this problem. We see less Giardia infected puppies who have been purchased from private breeders.
The bottom line is you need to have a stool sample checked as soon as possible.
Good Luck!
Dr. G.