The adult females deposit round, microscopic eggs. Each female lays thousands per day beginning about two months after the pig becomes infected. Eggs may survive for 10 or more years and are quite resistant to cold and disinfectants. They can be destroyed by high-pressure steam heat and sunlight. Because they are sticky, eggs are easily transported by cockroaches, beetles, flies, birds and workers' boots and clothing.
Eggs become infective after being outside the pig for one month.
When another pig swallows them, they hatch in the stomach or small intestine. The tiny larva that emerges penetrates the gut wall and is carried to the liver through the bloodstream. In the liver, larvae migrate for one-half to one week and then are swept through the bloodstream to the lungs. From there, the larvae are coughed up, swallowed and returned to the small intestine, where they grow and mature within two months. The significance of this is that clinical signs may occur before eggs are detectable in feces.