My first advice would be to go to the city animal shelter or to the SPCA to obtain a puppy or a dog. I have rescued two dogs and they have been healthy and good dogs. Next, the "breeder" probably runs a puppy mill and often those poor animals are neglected and unhealthy. You may have a breach of contract claim against the breeder. Was the sale in writing? Did the contract specify the dog is healthy? Did you have a certain amount of time to have the dog checked by a vet and return the dog for a refund if it was not healthy? Contact a local attorney through AVVO.com.
What you were told is irrelevant. What the terms of the contract were is the primary basis for your cause of action, if any. Also, VA may - indeed, probably - provide an implied warranty of merchantability.
A demand letter may suffice. Then again, a small claims complaint be required.
Call the VA and your county bar associations for referrals if you need to go farther.
The foregoing is for general information purposes and does not establish an attorney-client relationship.
First, these are probably "whip" worms. Puppies are born with worms and this is normal. Even with proper worming, there can be break through worms. Was there anything else wrong with the puppy? Simple worming will fix this problem (although you should always seek the advice of your REGULAR vet). What does your regular veterinarian say about the whip worms? Treatment should be very inexpensive and the breeder should be responsible for the cost of the medication, if they are a responsible breeder. Additionally, what does your contract say? Usually they will cover the cost of the medication. It is unlikely that you would receive the cost of the puppy unless you return the puppy. You should have a dog law attorney review your contract and contact the breeder.