Ascaris

• Ascaris lumbricoides

  Common names: Giant intestinal roundworm, Pink worm

  
• Ascaris lumbricoides

  • Biggest nematode infecting humans
  • Most common nematode of man
  • Soil-transmitted helminth (STH) along with Trichuris trichiura and hookworms - Triumvirate

  
• Diseases of poverty

  • Contribute to malnutrition and impairment of cognitive performance
  • Reduce work capacity and productivity in adults
• Epidemiology

  • Cosmopolitan distribution = world-wide, almost everywhere
  • 1.2 billion people globally affected
  • 2,000 die annually
  • 5 – 12 years old: Age group with highest intensity (children are vulnerable)
  • School-aged children: 27.7% affected
  • Preschool children: 30.9% affected
• Socioeconomic factors


  Affect the level of transmission of STH: Density of human population, Use of night soil as fertilizer, Illiteracy, Poor sanitation, Poor health education on hygiene
• Adult Ascaris lumbricoides

  • Habitat: Small intestine
  • Male: 10 – 31 cm long
  • Female: 22 – 35 cm long
  • Polymyarian somatic musculature arrangement
  • Anterior end: Mouth with three lips and sensory papillae, Small triangular buccal cavity
  • Posterior end: Male - Ventrally curved with two spicules, Female - Tapered
  • Reproductive Organ: Male - Single, long, tortuous tubule, Female - Paired reproductive organ
• Larva of Ascaris lumbricoides

  • Larval morphology is similar to the adult
  • Production of pepsin inhibitor 3 (PI-3): Protects the worm from digestion and phosphorylcholine that suppresses lymphocyte proliferation

  
• Ova of Ascaris lumbricoides

  • Golden-brown in color, Bile-stained
  • Three layers: Outer mamillated albuminous covering, Thick middle transparent protein layer, Inner lipid layer
  • Unfertilized: Size 85 – 95 um by 38 – 45 um, Shape variable, Embryo unembryonated, Shell thin, Usually corticated
  • Embryonated: Infective stage
  • Ova can be the diagnostic stage

  
• Life Cycle of Ascaris lumbricoides

  1. Embryonation in the soil: 2 – 3 weeks

  2. Heart-lung migration where larvae undergo molting

  3. Development of egg-laying adult worm: 9 – 11 weeks after ingestion

  4. Life span: 1 year

  5. Embryonation happens in the external environment

  6. Diagnostic stage: Fertilized or unfertilized egg, even the adult worm

  7. Infective stage: Embryonated eggs with third stage larvae

  8. Autoinfection: NO

  
• Pathogenesis and Clinical Manifestations

  • Majority asymptomatic
  • Pathology: Tissue reactions, Intestinal irritation, Other complications
  • Lung migration causing Loeffler's syndrome
  • Moderate intestinal infection: Lactose intolerance, Vitamin A malabsorption
  • Heavy Intestinal infection: Bowel obstruction from bolus formation, Intussusception, Volvulus that may result to bowel infarction and perforation
  • Constant biting and pricking of the intestinal mucosa by A. lumbricoides adult: Irritate nerve endings in the mucosa resulting to intestinal spasm → intestinal obstruction even with few adult worms
  • Erratic Parasite: Trachea, Bile duct causing bile duct obstruction, Pancreas causing pancreatitis, Appendix causing appendicitis
• Clinical Diagnosis

  Vague signs and symptoms, Passed out adult worm with the feces, Vomit out the adult worm, Demonstration of Ova, Recovery of adult worm in stool sputum, vomitus, Other Diagnostic Modalities: Radiography - Tramway sign on x-ray of abdomen

  
• Treatment

  1. Benzimidazoles like mebendazole and albendazole: Bind to the parasites' B-tubulin resulting to disruption of parasite microtubule polymerization

  2. Pyrantel pamoate: Depolarizing neuromuscular blocking drug that leads to spastic paralysis of worms leading to expulsion from the GIT

  3. Piperazine: Treatment for partial intestinal obstruction due to parasite bolus, GABA receptor antagonist causing flaccid paralysis of the worm
• Prevention and Control

  1. WASHED framework for the control of STH: Provision of safe water, Environmental sanitation, Hygiene education, Regular deworming

  2. War on Worms (WOW)

  3. Surveillance and monitoring of stool using Kato-Katz method: WHO recommendation, Stain: Malachite green

  4. Reinfection: Usually 4 months post-treatment, Full reinfection: 6 – 7 months post-treatment, Immediate reinfection after deworming is possible in communities with poor environmental sanitation
• Adult worms live in the lumen of the small intestine. A female may produce approximately 200,000 eggs per day, which are passed with the feces

  
• Unfertilized eggs may be ingested but are not infective. Larvae develop to infectivity within fertile eggs after 18 days to several weeks, depending on the environmental conditions (optimum: moist, warm, shaded soil)
• After infective eggs are swallowed

  1. The larvae hatch, invade the intestinal mucosa, and are carried via the portal, then systemic circulation to the lungs

  2. The larvae mature further in the lungs (10 to 14 days), penetrate the alveolar walls, ascend the bronchial tree to the throat, and are swallowed

  3. Upon reaching the small intestine, they develop into adult worms. Between 2 and 3 months are required from ingestion of the infective eggs to oviposition by the adult female

  4. Adult worms can live 1 to 2 years

  
• Ascaris lumbricoides summary

  • AKA: giant intestinal roundworm
  • IS: embryonated egg
  • DS: embryonated, unembryonated egg, adult worm
  • Disease: Sandbox infection, Ascaris pneumonitis, loeffler's syndrome, pot belly, bolus