Ascaris

Lisa A. Spacek, M.D., Ph.D.
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.
  • A soil-transmitted helminth, other STHs are Strongyloides stercoralis, Trichuris trichiura (whipworm), Ancylostoma duodenale and Necator americanus (hookworms).
    • Ova develop on warm, humid soil over a period of 3 wks before becoming infective.
    • Adult worms live in the lumen of the small intestine for up to 2 yrs.
    • Ova are excreted in stool, are hardy, and can sustain freezing, and live up to 6 years in moist soil.
    • Adult female worms can produce 200,000 ova/day.
  • 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.[2]

Epidemiology:

  • Endemic in warm, humid areas especially where human excreta is used as fertilizer or contaminated wastewater is used for irrigation.
  • Infection most common in the young, but affects all ages.
    • Heavy infections can cause malnutrition.[8]
  • Transmission: hand to mouth.
  • Ascariasis due to A. suum is a swine-associated zoonosis.[9]

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MICROBIOLOGY

  • Ascaris lumbricoides: largest intestinal nematode (roundworm) that is a human pathogen.
  • A soil-transmitted helminth, other STHs are Strongyloides stercoralis, Trichuris trichiura (whipworm), Ancylostoma duodenale and Necator americanus (hookworms).
    • Ova develop on warm, humid soil over a period of 3 wks before becoming infective.
    • Adult worms live in the lumen of the small intestine for up to 2 yrs.
    • Ova are excreted in stool, are hardy, and can sustain freezing, and live up to 6 years in moist soil.
    • Adult female worms can produce 200,000 ova/day.
  • 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.[2]

Epidemiology:

  • Endemic in warm, humid areas especially where human excreta is used as fertilizer or contaminated wastewater is used for irrigation.
  • Infection most common in the young, but affects all ages.
    • Heavy infections can cause malnutrition.[8]
  • Transmission: hand to mouth.
  • Ascariasis due to A. suum is a swine-associated zoonosis.[9]

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Last updated: July 4, 2021