Ascaris is a topic covered in the Johns Hopkins ABX Guide.

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MICROBIOLOGY

  • Ascaris lumbricoides: largest intestinal nematode (roundworm) that is a human pathogen.
    • Soil-transmitted helminth
      • Ova develop on warm, humid soil (about 3 wks) before becoming infective.
      • Adult worms live in lumen of small intestine (up to 2 yrs).
      • Ova excreted in stool.
  • Life cycle: humans ingest infective ova that hatch and release larvae. Larvae invade intestinal mucosa and travel from portal to systemic circulation to lungs in about 4 days. Larvae penetrate through alveoli, ascend the trachea, and are reingested, then mature in intestines and live for 10 to 24 months.[3]
  • Ova are hardy. They can sustain freezing and live up to 6 years in moist soil. Adult female worms can produce 200,000 ova/day.

Epidemiology:

  • Endemic in warm, humid areas especially where human excreta is used as fertilizer, contaminated wastewater is used for irrigation, or geophagy (deliberate/regular consumption of soil) is practiced.
  • Infection most common in young, but affects all ages.
    • Heavy infections can cause malnutrition.[6]
  • Transmission: hand to mouth.
  • Ascariasis due to A. suum is a swine-associated zoonosis.[7]

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Last updated: October 13, 2016