No, it isn't true. In fact the commonest way for puppies to get worms is to be born with roundworms, this is why they have to be wormed.

Do you HAVE worms?

HOW INFECTION OCCURS: toxocara adult adult Toxacara worms In dogs, there are four ways by which infection with Toxocara canis occurs: * Consuming infective worm eggs from soil in the environment (generally through normal grooming). * Nursing from an infected mother dog. * Consuming a prey animal (usually rodent) that is carrying developing worms. * During embryonic development when an infected mother dog is pregnant (most puppies are infected this way). Note: cats cannot be infected with Toxocara canis. LIFE AS A ROUNDWORM: Toxocara canis has one of the most amazing life cycle in the animal kingdom. It is crucial to understand this life cycle if effective treatment is to be pursued. Life Cycle Toxocara STEP ONE: Toxocara eggs are passed in the host’s feces. If a fecal sample is tested, the eggs can be detected. The embryonic worm develops in the outdoor environment inside its microscopic egg for one month before it becomes able to infect a new host. If environmental conditions are favorable, it takes about a month for the egg to become infective but Toxocara eggs are famous for weathering harsh environmental conditions. Eggs can remain infective for months to years. Note: Fresh feces is not infectious. dog lickingSTEP TWO: The egg containing what is called a “second stage larva” is picked up from the dirt by a dog or by some other animal. usually in the course of normal grooming. The egg hatches in the new host’s intestinal tract and the young worm burrows its way out of the intestinal tract to encyst in the host’s other body tissues. If the new host is a dog, the life cycle proceeds. If the new host is a member of another species, the larvae wait encysted until the new host is eaten by a dog. STEP THREE: These second stage larvae can remain encysted happily for years. If the host is a dog, the larvae mostly encyst in the host’s liver. When the time comes to move on, the larvae excyst and migrate to the host’s lungs where they develop into “third stage larvae.” They burrow into the small airways and travel upward towards the host’s throat. A heavy infection can produce a serious pneumonia. When they get to the upper airways, their presence generates coughing. The worms are coughed up into the host’s throat where they are swallowed thus entering the intestinal tract for the second time in their development. howparvo2If the host is pregnant, the larvae do not migrate to the lung after they excyst; instead they home to the uterus and infect the unborn puppies. The second stage larvae make their way to the puppies’ lungs to develop into third stage larvae. If the host is a nursing mother, second stage larvae can migrate to the mammary gland instead of the lung after excysting. Puppies can be infected by drinking their mother’s milk, though, due to the intrauterine cycle described above, the litter would probably already be infected. Note: When dogs are dewormed with traditional dewormers, this affects only worms in the intestinal tract. It does not affect encysted larvae. It is very difficult to prevent mother to puppy transmission and routine deworming is not adequate. It is possible to prevent infection in unborn puppies by using a specific daily protocol of fenbendazole (your veterinarian can provide details) or with the new generation product AdvantageMulti® (containing moxidectin). STEP FOUR: Once back in the intestine, the larvae complete their maturation and begin to mate. The first eggs are laid about one week after the fourth stage larvae have arrived in the intestine and about 4-5 weeks after infection has first occurred. From here the cycle repeats. http://www.marvistavet.com/html/body_roundworms_in_dogs___puppies.html Keep in mind, commercial wormers are POISON. Also, if you are a Raw Feeder, this is why we pretty much always FREEZE meats, especially game meats. Freezing kills bugs!