Puppies are particularly susceptible to worms. Exercise caution with your pet and their waste. The method of infection varies with the type of worm, but includes transmission via the milk while nursing, skin penetration, and oral ingestion. Gastrointestinal parasites can cause serious disorders in dogs, including life-threatening anaemia, loss of proteins from the body, loose motion, vomiting, low glucose in blood, intestinal obstruction, and weight loss.