Roundworms do not typically infest adults, and adult dogs do not usually show signs other than listed above. 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.
Pups can also get roundworm through mother's milk.
Nearly every puppy that is born with roundworms contracted from its mother. A severe infestation can cause death by intestinal blockage. Worming the bitch has no effect on the encysted larvae and cannot prevent the worms from infecting the puppies. Are another common pet invader. The males and females mate, and the female produces eggs that are passed in the feces.