S. stercoralis

• common name - threadworm
• pathogenesis - eosinophilia, anemia, recurrent diarrhea, secondary bacterial infections, chronic gastrointestinal inflammation
• habitat - small intestine
• reservoir host - perhaps dogs, apes
• infective form - filariform larva
• specimen of choice - feces
• Reproduction - ovoviviparous
• S. stercoralis eggs look the same with hookworm
• can infect both humans and dogs
• ovum is rarely seen in stool; hatches in the small intestine, can find rhabditiform larvae in feces instead; similar to hookworm spp. egg; may contain larva
• rhabditiform

  buccal cavity - short

  genital primordium - large and conspicuous

  tail - short and stubby
• adult male is seen only in free living cycle
• adult

  color - colorless

  Buccal structure - short

  copulatory bursa - absent

  spicules - two
• we can distinguish hookworm from threadworm by using one of the 3 fecal culture methods;

  1. Harada Mori
  2. Sand and Charcoal (Bearmann)
  3. Kogar Agar plate culture
• Kogar Agar Plate Culture is the most accurate culture method in distinguishing threadworm from hookworms
• Filariform larva

  S. stercoralis - long esophagus, notched/ forked tail

  Hookworms - long esophagus, pointed tail
• Rhabditiform larva

  S. stercoralis - short buccal cavity, large genital primordium

  Hookworms - long buccal cavity, short genital primordium
• Lifecycle

  1. Indirect - rhabditiform larva develop intro free living adult worm in the soil
  2. Direct - rhabditiform larva directly develop in the soil into filariform larvae that then infect the human host via active skin penetration
  3. Autoinfection - instead of being excreted in the stool, develop in the large intestine into filariform larvae that then penetrate the intestinal mucosa and migrate to other organs of the human host
• Parasitic cycle

  filariform larvae in contaminated soil penetraete human skin and migrate to the small intestine. L3 larvae migrate via blood stream and lymphatics to the lungs, but can also migrate to the intestine. In the small intestine, larvae molt twice and become adult female worms
• Free living cycle

  Rhabditiform larvae pass in stool of infected definitive host. Develop into infective filariform larvae or free living adult males and females. Hatch and become infective filariform (L3) larvae. Initiate parasitic cycle by penetrating human skin.
• Autoinfection

  Rhabditiform larvae in the gut becomes infective, resulting in autoinfection. once re-infective, they are carried to the lungs, pharynx, and small intestine or disseminate throughout the body