Roundworms are usually passed on to humans through contact with soil or dirt contaminated by dog or puppy feces. In humans, this can lead to vomiting and diarrhea. Dogs can also experience the same symptoms, and can trigger weight loss.
Medicines can remove the infection, but prevention is best. Do make sure that children do not play in areas where dogs are known to pass their waste. Adults should be careful about what they touch in such places, too.