Roundworms grow in the intestine laying thousands of eggs which pass out in the faeces (droppings). The eggs can survive for months or even years in the soil and need to lie in the environment for some time before they can infect another animal. They find their way into a new host either directly, when eaten by a cat or indirectly after being swallowed by a rodent which then is eaten by the cat. Inside the rodent - and sometimes in people - the egg hatches inside the gut, burrows through the intestine wall and lodges as a resting larval stage somewhere within the body. Immature worms also survive in the tissues of an infected cat. Immature worms can be passed from a mother to her kittens in the milk.