Toxocara canis infects a wide variety of animals but does not develop to maturity, remaining in the second juvenile stage. T. canis can cause viseral juveniles migrans. The symptoms are general poor health and pulmonary involvement. In older children there may be ocular involvement. The life cycle of T. leonina is simple.
Ingested eggs hatch in the small intestine, where the juveniles penetrate the mucosa.
After a period of growth, they molt and return directly to the intestinal lumen, where they mature. Although they are mildly pathogenic, their main importance is a diagnostic one because T. leonina is considered of little importance as a source of visceral larva migrans. Avoid ingesting the infective egg. A large proportion of puppies and kittens are infected at birth. Young children can easily become infected by ingesting eggs from play areas utilized by both humans and pets.