MICROBIOLOGY

• Members of the family Ancylostomatoidea (nematodes):
  
  • 18 total genera
  • Two species account for most human infections:
    • Ancylostoma duodenale (AD)
    • Necatur americanus (NA)
  • Estimated prevalence of 16.5% among school-aged children globally
• Adult hookworms are 5-11mm (males) or 9-13mm (females). Identification based on size, number and arrangement of teeth, length of esophagus, size of eggs, morphology of bursa (males), or position of ova (females). Eggs are morphologically indistinguishable.
  • AD [Fig 1]: head in same direction as body, 2 pairs of ventral teeth, larger than NA, caudal spine present.
  • NA [Fig 2]: head curved opposite body, dorsal and ventral semi-lunar cutting plates, caudal spine in female absent. Found in New World, including U.S.
• Life cycle: [Fig 3]
  
  • Eggs [Fig 4] are passed in the stool and hatch into rhabditiform larvae after 1-2 days.
  • Rhabditiform larvae grow in the soil, molt and become infective filariform larvae after 5-10 days.
  • Filariform larvae penetrate human skin, mostly feet, (AD can also enter via ingestion of contaminated food) and travel through venous circulation to lungs, through alveoli, to pharynx and are swallowed into the GI tract where they mature and attach to the walls of the small intestine.