Puppies and Deworming
The main parasites that we find in puppies are roundworms, hookworms, and whipworms. Of these, roundworms are the most common.
We assume that all puppies come to us with roundworms. If the mother has been exposed to roundworms at any point in her life, larvae from those worms will travel to the mammary tissue and go dormant. These are called "encysted larvae". When the mother becomes pregnant and begins to lactate, the larvae emerge from dormancy and travel to the milk ducts. When the puppy start to nurse, they get a dose of roundworm larvae along with the milk. Not very palatable, but an excellent survival adaptation on the part of the worms.
We follow the Canadian guidelines for the treatment of parasites in dogs and cats when determining how often to deworm puppies. The guidelines recommend deworming puppies at 2, 4, 6, and 8 weeks of age. If the breeder has not already completed this, we will recommend deworming the puppy every 2 weeks for a total of 4 treatments. If the breeder has already done 1 or 2 treatments, we will prescribe further treatments to make a total of 4. (I know we are talking about roundworms here, but the dewormers that kill roundworms are generally effective on the other worm types as well.)
Once the initial 4-treatment regimen is complete, we recommend deworming puppies monthly until 6 to 8 months of age. It is impossible to prevent puppies from picking up and eating things that we do not typically think of as food. Some of these things, like feces from other dogs or carcasses of small animals, may contain infectious parasites. Generally puppies are over this stage by 6-8 months of age and we can stop the monthly deworming.
There are important exceptions to the "stop at 8 months" recommendation. Canine roundworms are infectious to humans, especially to children (it is a hygiene thing). When dog roundworms infect children, they don't just stay in the intestine. The larvae travel through the tissues, including through abdominal organs like the liver, causing damage. They can even end up traveling into the eye and causing blindness. For this reason if the dog is in a home with small children we recommend monthly deworming as an adult as well.
Likewise, dogs that live in a home with an immunocompromised person should be dewormed on a monthly basis.
In this area all dog should be on a tick and flea preventive. Many of these preventives are available in a form that combines a dewormer with them, making monthly control of fleas, ticks, and internal parasites simpler.
(By the way - Why don't we do routine fecal testing in puppies? The common fecal testing that is done in clinic is called a fecal flotation. A sample of stool is examined, looking for parasite eggs. The one problem with this test is that worms in the intestine do not "lay" their eggs continuously. Not every piece of stool has parasite eggs in it, even when the puppy has an obvious infestation. Therefore, if we have a fecal flotation test that is negative we will still deworm that puppy, because we cannot know for sure that the puppy truly has no parasites. We assume that we may have simply analyzed a piece of stool that did not contain any parasite eggs. It does not make sense to do a test that is not going to affect the recommendations that we make for treatment. This does not mean that we never do parasite tests in puppies or dogs; it does mean that we do not have a blanket recommendation to test all puppies, all the time.)
Examples of dewormers:
Milbemycin (Interceptor, NexGard Spectra, others)
Praziquantel (Drontal Plus)