Introduction to Ascaris lumbricoides
Ascaris lumbricoides is a nematode (roundworm) commonly found in the human small intestine, causing an infection known as Ascariasis. These worms can grow up to 40 cm and have a cylindrical body protected by a thick cuticle. They are capable of producing thousands of eggs daily, which can spread through contaminated water or food. Children with heavy infections may face digestive problems, malnutrition, and stunted growth. Understanding the structure and life cycle of these roundworms is vital for learning how to prevent and control infections.
Structure of Ascaris lumbricoides
Basic Body Form
Ascaris lumbricoides is cylindrical with a pseudocoelom (a fluid-filled cavity).
It has bilateral symmetry, meaning the body can be divided into two similar halves.
Body Covering
The outer layer is a tough, non-cellular cuticle.
Beneath the cuticle lies the epidermis, which helps maintain body shape and protection.
Digestive System
The worm has a complete alimentary canal with a mouth, pharynx, intestine, and anus.
The mouth is surrounded by three lips, enabling it to ingest food from the host’s intestine.
Sexual Dimorphism
Males are smaller (up to 30 cm) with a curved tail end.
Females are longer (up to 40 cm) with a straight tail end and can lay thousands of eggs daily.
Excretory and Nervous System
Wastes are expelled through an excretory pore.
A simple nervous system coordinates basic movements.
Life Cycle of Ascaris lumbricoides
Egg Stage
Adult female worms in the small intestine release fertilised eggs into the intestines.
These eggs exit the body in faeces and become infective in soil within a few weeks under warm, moist conditions.
Larva Stage
When infective eggs are accidentally swallowed (via contaminated food or water), they hatch in the host’s intestine.
The larvae then move through the intestinal wall and travel via the bloodstream to the lungs.
After maturing in the lungs briefly, they ascend the respiratory tract to the throat and are swallowed again, returning to the intestine.
Adult Stage
Larvae develop into adult worms in the small intestine, feeding on the host’s intestinal contents.
Adult worms can survive for 1–2 years, with females laying thousands of eggs each day, continuing the infection cycle.
Quick Quiz (With Answers)
Which body part do Ascaris eggs primarily exit from in humans?
A. Mouth
B. Nose
C. Intestine
D. Skin
Answer: C (They are passed out in faeces through the intestine.)
Where do Ascaris larvae usually mature before returning to the intestine?
A. Stomach
B. Lungs
C. Pancreas
D. Gallbladder
Answer: B (They typically migrate to the lungs first.)
What is the lifespan of an adult Ascaris worm?
A. 1–2 years
B. 2–3 weeks
C. 5–6 months
D. 3–4 years
Answer: A (An adult worm can live for 1–2 years.)
FAQs on Ascaris lumbricoides Life Cycle & Structure
1. Can Ascaris infect other animals?
Yes, pigs are also a common host, and there have been reports of infection in dogs and monkeys as well.
2. How does one get rid of Ascaris worms?
Medications such as albendazole and mebendazole are commonly used to remove Ascaris worms.
3. Is Ascariasis always dangerous?
Mild infections might go unnoticed, but heavy infections can lead to serious issues like intestinal blockage and nutrient deficiencies.
4. How can children be protected from Ascaris?
Encourage frequent hand-washing, use of proper toilets, and ensure that their food and water are always clean.
5. Do Ascaris worms reproduce in the lungs?
No, they only mature briefly in the lungs before travelling to the intestine, where they reach adulthood and reproduce.
