Toxocara cati has one of the most amazing life cycle in the animal kingdom. It is crucial to understand this life cycle if effective treatment is to be pursued. Toxocara eggs are passed in the host's feces. If a fecal sample is tested, the eggs can be detected. The embryonic worm develops in the outdoor environment inside its microscopic egg for one month before it becomes able to infect a new host.
Eggs can remain infective for months to years.
The egg hatches in the new host's intestinal tract and the young worm burrows its way out of the intestinal tract to encyst in the host's other body tissues. If the new host is a cat, the life cycle proceeds. If the new host is a member of another species, the larvae wait encysted until the new host is eaten by a cat. If the host is a cat, the larvae mostly encyst in the host's liver. Most larvae waste no time and have arrived in the lung by the 3 rd day post-infection.