MICROBIOLOGY

• Members of the family Ancylostomatoidea (nematodes):
  
  • 18 total genera
  • Two species account for most human infections:
    • Ancylostoma duodenale (AD)
    • Necatur americanus (NA)
• Epidemiology:
  • One of the most common soil-transmitted helminths, with about 500 million people infected worldwide.
  • Hookworm prevalence is highest in adults, although children are also commonly infected.
  • Infections are common in the tropics and subtropics; rare in regions with < 40 inches of annual rainfall.
    • AD is found in Mediterranean countries, Iran, India, Pakistan, and the Far East.
    • NA is in sub-Saharan Africa, the Americas, Asia, and the South Pacific.
  • Anemia is the primary source of infection-related morbidity, driving global productivity losses that may exceed $100 billion annually.
• Adult hookworms are 5-11mm (males) or 9-13mm (females). Identification based on size, number and arrangement of teeth, length of the esophagus, size of eggs, the morphology of bursa (males), or position of ova (females). Eggs are morphologically indistinguishable.
  • AD [Fig 1]: head in the same direction as the body, two 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 the New World, including the 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), travel through venous circulation to the lungs, through alveoli, to the pharynx, and are swallowed into the GI tract where they mature and attach to the walls of the small intestine.