Life Cycle of the Ascaris Lumbricoides

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  • 0:03 What Is Ascaris Lumbricoides?
  • 1:11 The Ascaris Life Cycle
  • 2:35 Effects in Humans
  • 2:52 Lesson Summary
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Lesson Transcript
Instructor: Danielle Haak

Danielle has a PhD in Natural Resource Sciences and a MSc in Biological Sciences

Ascaris lumbricoides is a type of parasite that can infect humans. Like many parasites, they have a fascinating life cycle. In this lesson, learn how they spread, how they grow, and what effect they can have on humans.

What Is Ascaris Lumbricoides?

Warning: this lesson is not for the faint of heart or anyone currently eating lunch! Ascaris lumbricoides is a type of nematode, or roundworm, that can infect humans and live as a parasite in the small intestines. For simplicity, in the rest of the lesson we'll just call in Ascaris. Though uncommon in the United States, worldwide more than one billion people are infected with this parasite. It thrives in tropical and subtropical regions with inadequate sanitation and is especially common in kids under 10 years old.

Adult worms live one to two years. Females grow up to 35 cm in length (about 14 inches), and males grow up to 30 cm in length (about 12 inches). These are the largest intestinal nematodes that affect humans. Additionally, adult females can produce up to 200,000 eggs every single day. That's simultaneously cool and terrifying. Let's take a look at the life cycle of Ascaris so we can get a better idea of how it affects humans.

The Ascaris Life Cycle

Adults reside in the small intestines of humans and are either male or female. When a female releases fertilized eggs, they exit the human body through feces. Only fertilized eggs have the potential to infect a host (unfertilized eggs are expelled but don't go through any additional development). A fertilized egg is capable of infecting a host for anywhere between 18 days and several weeks, depending on the environmental conditions.

A host is infected by ingesting the fertilized eggs through the mouth. This happens when contaminated soil has not thoroughly been washed from the hands or food before being introduced to the mouth. Once the egg is in the mouth, it is swallowed and enters the digestive tract. After the egg has been swallowed, the larvae hatch, first colonizing the mucus that lines the small intestine and eventually making their way into the bloodstream where they move to the lungs.

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