The eggs pass out in the faeces of the dog and stick to the animal's fur or to grass. These eggs can survive for at least a year in the outside world, during which time they disperse widely.
Flies help to spread the eggs, as does the wind.
The adult tapeworms do not make their hosts ill. The eggs are then easily transferred from the hands to the mouth. After an egg has been swallowed, it hatches into an embryo, which burrows through the wall of the intestine into the blood stream. The embryo finally lodges in an organ, usually the liver or the lung. The parasite then grows to form a cyst filled with fluid.