Ascaris lumbricoides Structure and Life Cycle

Ascaris lumbricoides is a nematode roundworm that infects the small intestine of humans. Ascaris belongs to the phylum Aschelminthes. They are bilaterally symmetrical and have a pseudocoelom. The life cycle of Ascaris lumbricoides includes several stages including the release of fertilized eggs in human feces, formation of embryo outside the host body, ingestion by humans, and larval migration through the liver and lungs. In this article, we will study the structure and life cycle of Ascaris lumbricoides.

Ascaris lumbricoides

Ascaris lumbricoides is a parasitic worm that causes ascariasis in humans. It belongs to the family Ascarididae, order Ascaridida within the phylum Nematoda (roundworms). These worms are long and cylindrical in shape. They cause intestinal infections in vertebrates, including humans. These worms are prominently found in pigs. The life cycle of Ascaris lumbricoides starts with the release of fertilized eggs in human feces. Humans get infected by ingesting food or water contaminated with infective eggs.

The symptoms of Ascaris infection include severe abdominal pain, fatigue, vomiting, weight loss or malnutrition, and a worm in the vomit or stool. The migration of larvae through the lungs can lead to respiratory symptoms and eosinophilia. Good hygiene practices, sanitation, and proper disposal of human waste are essential for preventing Ascaris infections.

Ascaris Structure

The structure of Ascaris lumbricoides is as follows:

Body Shape

• Ascaris lumbricoides has a long and cylindrical body.
• Body is not segmented like other worms and is tapering at both the ends.
• Body is covered by chitinous cuticle that helps protect the worm.

Size

• Males are 2–4 mm in diameter and 15–31 cm in length. 
• Posterior end of male is curved ventrally and has a pointed tail.
• Females are 3–6 mm wide and 20–49 cm in length.

Mouth and Digestive System

• They have a well-developed mouth with three prominent lips.
• The alimentary canal is well developed with a muscular pharynx.
• Waste products are excreted through excretory pore.

Reproductive System

• Ascaris lumbricoides is dioecious, that is sexes are separate.
• In the reproductive structure, female produces egg and male produces sperm.
• Fertilized eggs are oval to round in shape and are 45–75 μm long and 35–50 μm wide. It has a thick outer shell.
• Unfertilized eggs measure 88–94 μm long and 44 μm wide.

Ascaris lumbricoides Egg

Ascaris lumbricoides eggs are oval or round in shape. Eggs are characterized by a thick, pitted outer shell and their size can range from 45 to 75 micrometers in diameter. Female can lay both fertilized and unfertilized eggs. These eggs contain a fertilized, multicellular embryo. After being excreted in the feces of infected individuals, the eggs undergo maturation in the external environment. After maturation the eggs become infective. The ingestion of contaminated food or water introduces the eggs into the human digestive system. In the small intestine the egg hatches and starts the life cycle of the parasitic worm.

Life Cycle of Ascaris lumbricoides

Life Cycle of Ascaris lumbricoides includes the following stages:

Egg Stage

• The life cycle begins with the release of fertilized eggs.
• In human beings, Ascaris live inside the walls of the small intestine.
• Female ascaris release fertilized eggs. Unfertilized eggs are not infective.
• The fertilized eggs are infected and are passed in the host’s feces.
• The eggs are thick-shelled and can survive in the environment for a long time.

The Larvae Stage

• Under favourable conditions like warm and moist soil the fertilised egg hatches.
• Larvae develop within the egg.
• The larva becomes infective after 18 days to several weeks. They can survive in the soil for several weeks to months.

Infection (Human Host)

• Humans become infected by ingesting food or water contaminated with soil containing infective Ascaris eggs.
• The eggs hatch in the small intestine, releasing larvae.

Migration and Development

• The larvae enters the mucosa of small intestine and and enter the bloodstream.
• The larvae moves to the other parts of the body like lungs and liver.
• In the lungs, the larvae ascend the bronchial tree, are coughed up, and then swallowed.

The Adult Stage-Return to the Small Intestine

• The larvae enters the throat so that the worms can be swallowed. It returns to the intestines to mature.
• Mating of adult male and female worms take place.
• The female produces large numbers of eggs.
• It takes around 2-3 months from ingestion of infective eggs to develop into mature adult male and female roundworm.
• Adult ascaris worms can live for about 1 to 2 years.
• The fertilized eggs consisting of larvae, are passed in the host’s feaces. It completes the life cycle of ascaris.

FAQs on Ascaris lumbricoides

1. What is the Structure of Ascaris lumbricoides?

Ascaris lumbricoides, is a parasitic roundworm, with a length of 15 to 35 cm. It has a long and cylindrical body. The body surface is smooth with white surface. It has a well developed mouth with three lips. Female is larger than males.

2. What is Ascaris lumbricoides Life Cycle?

The life cycle of Ascaris lumbricoides involves the ingestion of fertilized infective eggs. The egg hatches into larvae in the small intestine and migrate to lungs, liver. After reaching throat they get swallowed again and mature into adult worm in the small intestine and completes the life cycle.

3. What are the 5 Characteristics of Ascaris?

Ascaris have a long and cyclindrical body. Ascaris has a well-defined mouth with three lips.They show sexual dimorphism with female worm is larger than the male worm. The female Ascaris lays both unfertilized and fertilized eggs.

4. What is the Body Shape of Ascaris?

Ascaris lumbricoides has a long, cylindrical and tapered body.It appears elongated and round, with a smooth body surface. The size of worms range from 15 to 35 cm in length.

5. What is the Structure of the Ascaris Egg?

Ascaris eggs are spherical in shape. It measures around 45 to 75 micrometers in diameter. Egg have a thick, pitted outer shell. They are characterized by a fertilized, multicellular embryo within.