infections
Ascariasis
Transmission of ascariasis
Infection begins when a person swallows fertilizedAscariseggs. Only fertilized eggs can cause infection. People may swallow the eggs in food that came in contact with soil contaminated by human stool (feces) containing the eggs. Infection can also occur when people put their hands or fingers with contaminated dirt on them in their mouth.Ascariseggs are hardy and can survive in the soil for years. Once swallowed,Ascariseggs hatch and release larvae in the intestine. Each larva migrates through the wall of the small intestine and is carried through the lymphatic vessels and bloodstream to the lungs. Once inside the lungs, the larva passes into the air sacs (alveoli), moves up the respiratory tract and into the throat, and is swallowed. The larva matures in the small intestine, where it remains as an adult worm. This process takes 2 to 3 months. Adult worms range from 6 to 20 inches (15 to 51 centimeters) in length and from 1/10 to 2/10 inch (¼ to ½ centimeter) in diameter. They live 1 to 2 years. Eggs laid by the adult worms are excreted in stool, develop in the soil, and begin the cycle of infection again when they are ingested. People can also be infected withAscaris suumfrom pigs. Infection begins when a person swallows fertilized eggs because their hands were contaminated from touching infected pigs or from consuming undercooked vegetables or fruits contaminated with pig feces. WhetherAscaris suumis a distinct species fromAscaris lumbricoidesis debated. 