Toxascaris leonina

Toxascaris leonina is a common parasitic roundworm found in dogs, cats, foxes, and related host species. Toxascaris leonina, or T. leonina, is an ascarid nematode, a worldwide distributed helminth parasite which is in a division of eukaryotic parasites that, unlike external parasites such as lice and fleas, live inside their host. The definitive hosts of T. leonina include canids (dogs, foxes, etc.) and felines (cats), while the intermediate hosts are usually rodents, such as mice or rats. Infection occurs in the definitive host when the animal eats an infected rodent. While T. leonina can occur in either dogs or cats, it is far more frequent in cats. The life cycle of T. leonina is fairly simple. Eggs are ingested and hatch in the small intestine. The juveniles then penetrate the mucosal lining of the small intestine. After growth and molt, they return to the intestinal lumen and mature. The adult female worm lays eggs which are passed in the feces of the animal. The eggs become infective after 3–6 days in the environment. Cats can become infected by ingesting either the egg or rodents that contain the larvae. Rodents are usually the intermediate hosts of T. leonina. The rodent ingests the eggs and, once the eggs are hatched, the larvae migrate through the tissues of the rodent. The definitive host is then infected with this parasite when it eats an infected rodent. The egg of the T. leonina is usually more oval than round. The prepatent period for T. leonina is two to three months. The adult worms are usually 3-4 inches long and can be seen in the feces and vomit of the animal. Toxascaris leonina differs from other Toxocara in that the larvae do not migrate through the lungs; but rather, the entire developmental cycle occurs in the gut.