These parasites are mature by the time pups are three weeks of age. Nursing bitches can be infected with immature forms shed in the feces of their pups. Parasites depend upon their host for survival. Thus it is in the parasites best interest not to kill its host. However large infestations of ascarid worms can cause significant problems.
Large numbers can cause obstruction of the small intestine.
They can migrate into and obstruct the bile duct. An owner may notice a general unthriftiness and poor quality hair coat. With heavy infestations worms may be vomited or passed in the stool. In the majority of pets with ascarid infections no outward signs are apparent. In these cases detection and diagnosis requires a microscopic examination of the feces.