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]