strongyloides stercoralis

• Strongyloidiasis


  Threadworm infection
• Strongyloides stercoralis egg

  • Slightly smaller than hookworm eggs, averaging 48 by 35 µm
  • Well-developed larvae are almost always contained in the eggs
  • Two-, four-, or eight-cell stage of embryonic cleavage is surrounded by a thin hyaline shell
• Strongyloides stercoralis rhabditiform larva

  • Average size of 220 by 15 µm
  • Short buccal cavity
  • Prominent genital primordium
• Strongyloides stercoralis filariform larva

  • Average length of 690 µm
  • Long esophagus
  • Notched tail
• Strongyloides stercoralis adult female

  • Approximately 2 by 0.4 mm
  • Colorless, transparent body
  • Finely striated cuticle
  • Short buccal cavity
  • Long and slender esophagus
• Laboratory diagnosis of threadworm

  1. Diagnostic eggs may be present in stool samples

  2. Diagnostic rhabditiform larvae may be recovered in fresh stool samples and duodenal aspirates

  3. Sputum samples may yield S. stercoralis larvae in patients with disseminated disease

  4. Serologic tests like ELISA have been developed
• Threadworm life cycle

  • Direct cycle similar to hookworm
  • Indirect cycle with free-living adults
  • Autoinfection with filariform larvae developing inside the intestine
• Strongyloides is found predominantly in the tropical and subtropical regions of the world
• Those at risk for contracting threadworm are those who come into skin contact with contaminated soil, and persons living in institutions with poor sanitation
• Asymptomatic

  Patients with light infection often remain asymptomatic
• Strongyloidiasis


  • Symptoms include diarrhea, abdominal pain, urticaria, eosinophilia, vomiting, constipation, weight loss, anemia, malabsorption syndrome, itchy and red skin, allergic reactions, and pulmonary symptoms
  • Immunocompromised persons may suffer from severe autoinfections
• Treatment

  Ivermectin with albendazole as an alternative
• Prevention and control


  Proper handling and disposal of fecal material, adequate protection of skin from contaminated soil, and prompt treatment of infected persons
• Strongyloidiasis is caused by Strongyloides stercoralis.
• Strongyloides stercoralis


  Threadworm, the only species of this genus which is naturally pathogenic to humans
• Strongyloides stercoralis

  • Has free-living rhabditiform and parasitic filariform stages
  • Several species have been reported in mammals and in birds
• The parasitic or filariform female Strongyloides stercoralis is 2.2 mm by 0.04 mm, colorless, semi-transparent, with a finely striated cuticle
• The parasitic or filariform female Strongyloides stercoralis has a slender tapering anterior end and a short conical pointed tail
• The parasitic or filariform female Strongyloides stercoralis has a short buccal cavity with four indistinct lips
• The parasitic or filariform female Strongyloides stercoralis has a long slender esophagus extending to the anterior fourth of the body, and the intestine is continuous to the subterminal anus
• The parasitic or filariform female Strongyloides stercoralis has a vulva located one-third the length of the body from the posterior end
• The parasitic or filariform female Strongyloides stercoralis has uteri containing a single file of 8 to 12 thin-shelled, transparent, segmented ova, 50 to 58 μm by 30 to 34 μm
• The free-living female Strongyloides stercoralis measures 1 mm by 0.06 mm and is smaller than the parasitic female
• The free-living female Strongyloides stercoralis has a muscular double-bulbed esophagus, and the intestine is a straight cylindrical tube
• The free-living male Strongyloides stercoralis, measuring 0.7 mm by 0.04 mm, is smaller than the female, and has a ventrally curved tail, two copulatory spicules, a gubernaculum, but no caudal alae
• Parasitic males of Strongyloides stercoralis have not been reliably identified
• The rhabditiform larva of Strongyloides stercoralis measures 225 μm by 16 μm and has an elongated esophagus with a pyriform posterior bulb
• The rhabditiform larva of Strongyloides stercoralis is slightly smaller and less attenuated posteriorly than the hookworm larva, and has a shorter buccal capsule and a larger genital primordium
• The infective filariform larva of Strongyloides stercoralis is non-feeding, slender, and about 550 μm in length
• The infective filariform larva of Strongyloides stercoralis is similar to the hookworm filariform larva but is usually smaller, with a distinct cleft at the tip of the tail
• The eggs of Strongyloides stercoralis have a clear thin shell and are similar to those of hookworms except that they measure only about 50 to 58 μm by 30 to 34 μm
• Life cycle of Strongyloides stercoralis

  1. Free-living forms found in soil

  2. Female lays embryonated eggs that develop into rhabditiform larvae

  3. Rhabditiform larvae feed on organic matter and transform into free-living adults

  4. When conditions unfavorable, rhabditiform larvae develop into infective filariform larvae

  5. Filariform larvae infect humans through skin

  6. Parasites enter circulation, pass through lungs, migrate to larynx, and are swallowed

  7. Larvae develop into adults in duodenum

  8. Females reproduce by parthenogenesis, invade intestinal mucosa and deposit eggs

  9. Eggs hatch into rhabditiform larvae that migrate into lumen and pass out in feces

  10. Autoinfection occurs when rhabditiform larvae develop into infective filariform larvae that reinfect the host

  
• Acute strongyloidiasis


  • Invasion of skin by filariform larvae
  • Migration of larvae through body
  • Penetration of intestinal mucosa by adult female worms

  
• Light infection with Strongyloides stercoralis does not cause intestinal symptoms
• Moderate infection with Strongyloides stercoralis causes diarrhea alternating with constipation
• Heavy infection with Strongyloides stercoralis produces intractable, painless, intermittent diarrhea (Cochin China diarrhea) characterized by numerous episodes of watery and bloody stools
• Hyperinfection


  A syndrome of accelerated autoinfection which usually, but not invariably, occurs in the immunocompromised
• Hyperinfection with Strongyloides stercoralis manifests with exacerbation of gastrointestinal and pulmonary symptoms and increased numbers of larvae in the stool and/or sputum
• Chronic strongyloidiasis is often asymptomatic, but intermittent vomiting, diarrhea, constipation, and borborygmi may be observed
• Anal pruritus, urticaria, and larva currens rashes are also common in chronic Strongyloides stercoralis infection