Causes

Ascariasis isn't spread directly from person to person. Instead, a person has to come into contact with soil mixed with human or pig feces that contain ascariasis eggs or infected water. In some developing countries, human feces are used for fertilizer, or poor sanitary facilities allow human waste to mix with soil in yards, ditches and fields. People can also get it from eating uncooked pig or chicken liver that is infected.

Small children often play in dirt, and infection can occur if they put their dirty fingers in their mouths. Unwashed fruits or vegetables grown in contaminated soil also can transmit the ascariasis eggs.

Life cycle of a worm

• Ingestion. The tiny (microscopic) ascariasis eggs can't become infective without coming into contact with soil. People can accidentally ingest (swallow) contaminated soil through hand-to-mouth contact or by eating uncooked fruits or vegetables that have been grown in contaminated soil.
• Migration. Larvae hatch from the eggs in your small intestine and then go through the intestinal wall to travel to the heart and lungs via the bloodstream or lymphatic system. After maturing for about 10 to 14 days in your lungs, the larvae break into your airway and travel up the throat, where they're coughed up and swallowed.
• Maturation. Once they're back in the intestines, the parasites grow into male or female worms. Female worms can be more than 15 inches (40 centimeters) long and a little less than a quarter inch (6 millimeters) in diameter. Male worms are generally smaller.
• Reproduction. Female worms can produce 200,000 eggs a day if there are both female and male worms in the intestines, and the eggs leave your body in feces. The fertilized eggs must be in soil for at least two to four weeks before they become infective.

The whole process — from egg ingestion to egg deposits — takes about two or three months. Ascariasis worms can live inside your body for a year or two.