How Do These Worms Get Around

Through a complex lifecycle. Toxocara can be transferred across the placenta to unborn pups in the womb, and later in the bitch's milk. Also the bitch can be re-infected by her pups when she is cleaning or licking them.
 

Eggs or larvae can be passed out in the faeces and, within three weeks, a young pup with only a mild infection can be shedding Toxocara eggs-an adult Toxocara worm can produce 25,000 - 80,000 eggs per day. Having a thick and sticky shell the eggs can survive in the environment for two to four years. Being sticky means they cling to fingers or food and can be picked up even when there is no sign of  dogs faeces.

Routes of infection in pups, 98% of infection from the L2 migrating larvae before birth. 2% of infection from L3 larvae in bitches milk. They can also he transferred through an intermediate (paratenic) host. For example a dog may he infected by eating a mouse or a rabbit carrying the roundworm larvae.