Adult roundworms live in the dog's small intestine.

What they do:
Cause diarrhea, vomiting, stunted growth, rough coat, bloated belly.

How they spread:
Almost all puppies get roundworms from their mothers. Dogs can also pick up roundworms from the soil.

Defending against them: Once a month prevention is recommended.

Roundworms are active in the intestines of puppies, often causing a pot-bellied appearance and poor growth. The worms may be seen in vomit or stool; a severe infestation can cause death by intestinal blockage.

This worm can grow to seven inches in length. Females can produce 200 thousand eggs in a day, eggs that are protected by a hard shell and can exist in the soil for years. Dogs become infected by ingesting worm eggs from contaminated soil. The eggs hatch in the intestine and the resulting larva are carried to the lungs by the bloodstream.

The larva then crawls up the windpipe and gets swallowed, often causing the pup to cough or gag. Once the larvae return to the intestine, they grow into adults.

Roundworms do not typically infest adults. However, as mentioned above, the larvae can encyst in body tissue of adult bitches and activate during the last stages of pregnancy to infest puppies. Worming the bitch has no effect on the encysted larvae and cannot prevent the worms from infecting the puppies.