Ascarids are common intestinal parasites of dogs. They are also well-known causes of larva migrans syndromes in humans, especially children.
The most common worm that is of concern is the round worm. Not all worms are the same. The ones that infect animals or people are either round worms or flat worms (tape worms and flukes). What you commonly hear called 'puppy worms' is an infestation of ascrids.
Ascrids are extremely common. The vast majority of puppies are born with this particular round worm because it is transmitted in the uterus from momma to puppy. In addition to being infected that way, adult dogs can become infected by swallowing the egg of the worm or by swallowing infected prey.
If a person accidentally ingests some material that is contaminated with dog stool they then have the baby form of the parasite. This is what is known as visceral larva migrans. When you swallow that egg, the baby worm hatches and goes through the intestine and into the blood stream, and the first place it's caught is in the liver. But if it gets through the liver, it can get out into the lung and into the brain and other tissues.
Treatment: The infected individual never ever passes the egg in his or her stool. So the only way to check is with blood studies where a doctor would look for the antibody.
Once the infection has been established, medications are of limited value. The only time you can really jump in and effectively treat a worm infestation is right after the ingestion, before the worm has a chance to settle down in tissue.
The best protocol is to keep your dog on a monthly heartworm medication. These medications have a broad spectrum and can kill many types of worms, including round worms.
Leonard Marcus, M.D., D.V.M., is a member of the American Society of Tropical Medicine and Hygiene