ASCARIS LUMBRICOIDES

 

1. ASCARIS LUMBRICOIDES

1. Morphology

  • Ascaris lumbricoides is the largest intestinal nematode (roundworm) that infects humans.
  • Adults:
    • Males are 15-31 cm long, with a curved posterior end.
    • Females are 20-49 cm long, with a straight posterior end.
    • The worms are cylindrical with a whitish or pinkish color.
    • They have three prominent lips around the mouth.
  • Eggs:
    • Fertilized eggs: Oval, thick shell with a brown, bumpy outer layer (mammillated coat).
    • Unfertilized eggs: Elongated and thinner with irregular shells.
    • Eggs are extremely resistant to environmental factors and can survive in soil for years.

 

 

Ascaris lumbricoides Structure and Life Cycle: Introduction, Diagram and Life Cycle, FAQs

 

2. Life Cycle

  1. Ingestion of eggs:
    • Humans acquire infection by ingesting embryonated eggs present in contaminated food, water, or soil.
  2. Larval migration:
    • After ingestion, eggs hatch in the small intestine, releasing larvae.
    • The larvae penetrate the intestinal wall, enter the bloodstream, and travel to the liver, heart, and then the lungs (via the pulmonary circulation).
  3. Lung phase:
    • In the lungs, larvae mature further and cause respiratory symptoms. They eventually migrate to the bronchi and trachea.
    • Larvae are coughed up and swallowed, returning to the intestine.
  4. Maturation in intestines:
    • In the intestines, larvae mature into adult worms within 2-3 months.
    • Adult worms live in the small intestine, where they can survive for 1-2 years.
  5. Egg production:
    • Female worms lay thousands of eggs daily, which are excreted in feces.
    • Eggs must embryonate in the soil to become infectious.

Life cycle of ascariasis

3. Clinical Manifestations

In most cases, infections are asymptomatic, but severe infections can cause significant health problems.

  1. Intestinal phase (due to adult worms):
    • Abdominal pain, nausea, vomiting, diarrhea, or constipation.
    • Malnutrition and growth retardation in children.
    • Large worm burdens can cause intestinal obstruction, which may require surgical intervention.
    • Adult worms may migrate, causing appendicitis or blockages in the bile ducts or pancreatic ducts.
  2. Lung phase (due to larval migration):
    • Symptoms resemble Löffler's syndrome: cough, wheezing, fever, and dyspnea (difficulty breathing). Chest X-rays may show eosinophilic infiltrates (transient lung lesions).
  3. Systemic reactions:
    • Eosinophilia is common during larval migration.
    • Heavy infections can lead to fatigue and nutrient deficiencies.

 

4. Laboratory Diagnosis

  1. Stool examination:
    • The most common diagnostic method. Microscopic examination of stool samples can reveal fertilized or unfertilized eggs.
  2. Imaging studies:
    • Ultrasound, X-ray, or CT scans can sometimes reveal adult worms, especially in the case of intestinal or biliary obstruction.
  3. Blood tests:
    • Eosinophilia may be detected, especially during larval migration.
  4. Serology:
    • Occasionally used to detect antibodies against Ascaris lumbricoides, but it is not the primary diagnostic method.

5. Treatment

  • Antihelminthic drugs:
    1. Albendazole (400 mg, single dose): Disrupts the worm’s glucose metabolism, leading to its death.
    2. Mebendazole (100 mg twice daily for 3 days or 500 mg single dose): Inhibits microtubule formation in the worm.
    3. Pyrantel pamoate: A neuromuscular blocker that paralyzes the worm, making it easier to expel.
    4. Ivermectin: Sometimes used in resistant or heavy infections.
  • Supportive care:
    • For intestinal obstructions, nasogastric decompression may be required.
    • In severe cases, surgery might be needed to remove the obstructing worms.
  • Prevention of reinfection:
    • Good hygiene (hand washing before eating and after defecation).
    • Proper disposal of feces and avoiding the use of untreated human waste as fertilizer.
    • Washing fruits and vegetables thoroughly before consumption.

 

6. Prevention and Control

  • Public health measures:
    • Improvements in sanitation and access to clean water.
    • Regular deworming programs in endemic areas to control infection.
  • Health education:
    • Teaching children and communities about the importance of personal hygiene.

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