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===Cycle 2===
===Cycle 2===
In older dogs (above 3 months) the migration changes and the hepato-tracheal route occurs far less often, though can still occur. In these animals the L3 larvae hatch in the small intestine and travel to a wide variety of tissues throughout the body. Once the larvae have reached a tissue they will begin hypobiosis and encyst in the tissue until reactivated. In some animals the hypobiotic larvae will not reactivate and this will be the end of their life cycle.
In older dogs (above 3 months) the migration changes and the hepato-tracheal route occurs far less often, though can still occur. In these animals the L3 larvae hatch in the small intestine and travel to a wide variety of tissues throughout the body. Once the larvae have reached a tissue they will begin hypobiosis and encyst in the tissue until reactivated. In some animals the hypobiotic larvae will not reactivate and this will be the end of their life cycle.
===Cycle 3===
In the pregnant bitch larvae that have become hypobiotic as described in cycle 2 above are reactivated by hormonal changes. These larvae become mobile about three weeks before parturition and migrate across the placenta to the lungs of the fetus. Within the fetal lungs the larvae moult just prior to birth. From the lungs the larvae complete their life cycle in the same way as in the young animal, by being coughed and swallowed to enter the small intestine. The adults will then produce eggs which are released in the faeces as normal.
===Cycle 4===
The final life cycle involves transmission of L3 larvae to pups through the milk. Hypobiotic L3 larvae are reactivated and are either already present in the mammary glands or travel to them and are capable of passing in the milk during the first 3 weeks of lactation. There is no further migration in the pup when the larvae are ingested in this way and the remaining life cycle of the worm is completed in the small intestine of the pup.
As well as the above life cycles ''T. canis'' can infect paratenic hosts such as mice, rats and some birds. In these animals the L3 larvae migrate to tissues hypobiose until the hosts tissues are consumed by a dog in which the worm can complete its life cycle.