The worm larvae can also be transferred to the nursing pup or kitten from the mother's milk. The larvae make their way to the intestinal tract where they can grow up to five inches in length. They start shedding eggs and try desperately to keep house in the small intestine of the pup or kitten. The eggs that the adult worms pass in the stool can now reinfest the same pup or kitten or other dogs and cats if somehow the egg-bearing stool is eaten. Roundworms are active in the intestines of puppies and kittens, often causing a pot-bellied appearance and poor growth.
Roundworms can infest adult dogs and cats, too.
However, as mentioned above, the larvae can encyst in body tissue of adult dogs and cats, remain dormant for periods of time, and can activate during the last stages of pregnancy to infest the puppies and kittens. Worming the mother has no effect on the encysted larvae in the body tissues and cannot prevent the worms from infecting the newborn. Hookworms These are much more common in dogs than in cats. They are very small, thin worms that fasten to the wall of the small intestine and suck blood. Dogs get hookworms from larval migration in the uterus, from contact with the larvae in stool-contaminated soil, or from ingesting the eggs after birth.