Life Cycle of Ascaris Species

The life cycle of the Ascaris parasite is complex and takes place almost entirely within the host's body. A number of organ systems are involved, particularly the intestines and lungs.

About Ascaris Species

• The Ascaris parasite is a nematode worm. Ascaris lumbricoides affects humans, while A. suum is a related species that affects pigs. Both species have a similar life cycle.

Eggs

• Ascaris eggs can remain viable in soil for up to two years.

  Ascaris eggs are shed in feces by a previous host. They are golden brown in color and can remain viable in the soil for up to two years. They enter a new host by ingestion. For example, infection can happen if a person touches contaminated soil and then eats or prepares food without washing their hands.

Larvae

• Ascaris larvae hatch in the small intestine, burrow into the intestinal lining, and are carried through the bloodstream past the liver and the right side of the heart, into the lungs via the pulmonary artery. After molting twice, they burrow into the lung tissue, where they cause irritation and are coughed up by the host. They are then swallowed and re-enter the intestines.

Adults

• The larvae, which have grown about 10 times their original length of about 0.2 to 0.3 mm, undergo a final molt and reach sexual maturity in the small intestine. The Ascaris' life cycle takes about three months. They mate while living on undigested food in the intestine, and the eggs are passed with the feces to restart the cycle.

Infection

• Handwashing is the best way to prevent infection by Ascaris species.

  Ascaris lumbricoides is found worldwide, with the greatest prevalence in warm climates. It depends on poor sanitation and poor hygiene for its spread. Eggs can contaminate soil when people fail to wash hands after using the bathroom, then participate in outdoor activities. Handwashing after using the bathroom and after coming into contact with soil can prevent Ascaris infection.