Puppies and Kittens are often born with intestinal parasites.   Adult dogs and cats are also susceptible to picking up intestinal parasites.    Some intestinal parasites are zoonotic , meaning  that they can be passed from our pets to us.    Puppies are dewormed  every 2 weeks until 12 weeks of age, then monthly  until 6 months of age.   Kittens are dewormed every 2 weeks for 3 doses.        Adult cats who will go outside should be dewormed every couple of months especially if they are hunters.   Dogs generally are given intestinal parasite prevention on a monthly basis as medication is usually included in their heartworm and flea prevention medicine.
Deworming your pets properly is important for protecting your pets , children, senior citizens and immune-compromised individuals.    It is recommended to have your pets stool tested at least twice per year.... sometimes more often with puppies and kittens.