Questions and Answers
What are the primary species involved in human infections from the phylum Nemathelminthes?
Ascaris lumbricoides is also known as the Giant Roundworm.
True
What is the infective stage of Ascaris lumbricoides?
L3 larvae
How many eggs does a female Ascaris lumbricoides produce daily?
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Adult Ascaris lumbricoides can live for up to ______ years.
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Which of the following stages is the diagnostic stage for Ascaris lumbricoides?
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What can heavy infections of Ascaris lumbricoides cause in children?
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What is the length range of adult female Ascaris lumbricoides?
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Ascaris lumbricoides larvae mature in the ______ over 10 to 14 days.
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The outer layer of Ascaris lumbricoides fertilized eggs is often absent.
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Study Notes
Medically Important Metazoan Helminths
- Phylum Nemathelminthes is known for its roundworms, with "nematos" meaning thread and "helminths" meaning worm.
- Class Nematoda includes several important species affecting human health.
Ascaris lumbricoides
- Primary helminth species causing human infections worldwide; also known as the Giant Roundworm.
- Adult worms reside in the lumen of the small intestine, with females producing approximately 200,000 eggs daily, expelled via feces.
- Infective stage is the L3 larvae, while the diagnostic stages include both fertilized and unfertilized eggs.
Life Cycle
- Unfertilized eggs can be ingested but are non-infective.
- After favorable conditions, embryonated eggs develop L3 larvae over 18 days to several weeks in moist, warm, shaded soil.
- Ingestion of embryonated eggs leads to hatching of larvae that invade the intestinal mucosa, enter portal circulation, and reach the lungs, where maturation occurs over 10 to 14 days.
- Larvae then ascend the bronchial tree, travel to the throat, and are swallowed back into the small intestine to mature into adult worms.
- Complete cycle from egg ingestion to oviposition is about 2 to 3 months, with adult worms living for 1 to 2 years.
Morphology
- Ascaris lumbricoides worms are notably large, with female lengths of 20-35 cm and males 15-30 cm.
- Fertilized eggs show a rounded, thick shell often stained by brown bile, measuring 45 to 75 μm.
- Unfertilized eggs are elongated, larger with a thinner shell, measuring around 90 μm, containing refractile granules.
- Adult females have a straight tail, while males have a curved tail and possess three lips at the anterior end.
Clinical Presentation
- Adult worms typically do not cause acute symptoms; however, heavy infections can lead to significant health issues:
- Stunted growth and malnutrition in children.
- Abdominal pain, intestinal obstruction, and risks of perforation from migrating worms.
- Symptoms can include loss of appetite, vomiting, nausea, potential biliary tract obstruction, appendicitis, and expulsion of worms from the nasopharynx.
Diagnosis
- Diagnosis is achieved through microscopic identification of A. lumbricoides eggs in stool.
- Stool specimens must be collected, preserved in fixative, and concentrated using the formalin-ethyl acetate sedimentation technique for accurate identification.
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Description
This quiz covers the medically significant helminths found in the phylum Nemathelminthes, specifically focusing on Class Nematoda. Learn about various roundworm species, their characteristics, and their relevance to human health. Test your knowledge on Ascaris lumbricoides and other important parasites.
