Strongloides

• Strongyloides Stercoralis


  Threadworm
• Classification


  • Metazoa
  • Nematoda
  • Threadworm
• Morphology forms


  • Ovum
  • Adult
  • Larvae
• Adult morphology


  • Small, transparent, and filiform
  • Oesophagus occupies the anterior third of the body
  • Females larger than males
• Parasitic female size
• Free-living worm size
• Egg characteristics


  • Thin shelled
  • Transparent
  • Ovoid (55 um by 30um)
  • Partially embryonated
  • Not seen in stool
• Rhabditiform larvae


  • Lack of sheath
  • Length of pharynx
  • Presence of smaller buccal capsule
• Strongyloides Stercoralis co-exists with hookworm infection
• Epidemiology


  • Widely distributed (50 to 100 million cases worldwide)
  • Common in tropical and subtropical areas with poor sanitation
  • Prevalent in the South U.S.
• Life cycle types


  • Indirect
  • Auto infection
  • Direct
• If no suitable host is found, the larvae mature into free-living worms
• Filariform larvae can penetrate the mucosa and cycle back into blood circulation
• Life cycle of S. stercoralis

  1. Infective larvae penetrate the skin

  2. Enter venous circulation

  3. Right heart to lungs

  4. Penetrate into alveoli

  5. Young adults ascend to glottis

  6. Swallowed and develop into adults
• Ovipositing females develop in 28 days from infection
• Pathogenesis


  1. Eggs hatch in intestinal mucosa

  2. Develop into rhabditiform larvae

  3. Passed in faeces

  4. Develop into infective filariform larvae

  5. Enter another host to complete the direct cycle
• Secondary infection of the damaged mucosa can lead to serious complications
• Disseminated occurs in immuno-deficient individuals
• Treatment and Control


  • Ivermectin
  • Thiabendozole
  • Control similar to that of Hookworm
  • Auto-infection controlled by chemotherapy
  • Direct and indirect infections controlled by improved hygiene
• Transmission of intestinal parasites can occur through ingestion of parasite ova/cyst in food/water
• Transmission methods


  • Ingestion of parasite ova/cyst in food/water
  • Skin penetration
  • Ingestion of parasite in raw or semi-cooked meat
  • Ingestion of parasite in raw or uncooked fish
  • Water contact
• Clinical manifestations of intestinal parasites

  • Abdominal discomfort
  • Nausea
  • Vomiting
  • Diarrhoea with blood or mucus
  • Diarrhoea without blood
  • Ulcers
  • Peritonitis
  • Weight loss
  • Anaemia
• Examples of parasites associated with specific clinical presentations

  • Dysentery: E. histolytica, Balantidium coli, Trichuris trichiura, S. mansoni, S. stercoralis
  • Malabsorption syndrome: Giardia lamblia, Cryptosporidium, S. stercoralis, Isospora belli
  • Pruritus ani: E. vermicularis, Taenia species, S. stercoralis, Hymenolepis nana
• Treatment of intestinal parasites

  • Metronidazole
  • Albendazole
  • Mebendazole
  • Praziquantel
  • Niclosamide