Ascariasis isn't spread directly from person to person. Instead, a person has to come into contact with soil mixed with human feces that contain ascaris eggs. In many developing countries, human feces are used for fertilizer or poor sanitary facilities allow human waste to mix with local soil in yards, ditches and fields.

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

Life cycle of a worm

  • Ingestion. The microscopic ascariasis eggs can't become infective without coming into contact with soil. People can accidentally ingest 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 penetrate the intestinal wall to travel to your lungs via your bloodstream or lymphatic system. After maturing for about a week in your lungs, the larvae break into your airway and travel up your throat, where they're coughed up and swallowed.
  • Maturation. Once 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. Male and female worms mate in the small intestine. Female worms can produce 200,000 eggs a day. You expel the eggs in your feces. The fertilized eggs must be in soil for at least 18 days before they become infective.

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

May. 25, 2012