2. Introduction
• Strongyloides stercoralis is a human parasitic roundworm, commonly
known as threadworm.
• Inhabit small intestine mucosa (duodenum &jejunum)
• Causing the disease strongyloidiasis.
• It is soil transmitted infection (infective stage is larva found in soil)
• The disease can also found in dogs and cats .2
3. Geographical distribution:
• Strongyloides is exist on all continents except for Antarctica.
• It is most common in the tropics, subtropics regions.
• Has a very low prevalence in developed economies where fecal contamination
of soil or water is rare.
• Very common in developing countries, but it is less prevalent in urban areas
than in rural areas (where sanitation standards are poor).
• More predominant in the areas where there is agriculture activities, because
they provide favorable conditions for development of this worm.
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5. Morphology (the worm)
Shape: cylindrical
Color: pink- creamy –grey
Size: very small
Male: 0.7 – 1.0 mm long
Female: 1.0 -2.7 mm long
Habitat: mucosa of small intestine
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6. Development of worm
Egg contain L1 L2 L3
infective stage
• The worms lay eggs containing L1 (oviviviparous )
• L1 develop into L2, then L3
• L3 infective to man, in man it develop into L4 and
L5, then worms.
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7. Larva of S. stercoralis
• Size: 380 x20 µm
• Esophagus : rhabditiform
• Buccal cavity is short.
• Ovoid genital premordium on the
middle of the ventral side
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9. life cycle:
Has two types alternates between free-living and parasitic
cycles (hetrogenic)
1- Parasitic cycle:
Occur in human (adult worm develop in man intestine)
2- free living cycle:
Occur in soil (adult worm develop in soil)
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10. How man become infected?
• Man become infected when L3 (filariform
larva) penetrate through the skin from the
soil.
• from the skin the larva has 2 ways to
reach the small intestine:
1- Classic way
2- Direct way
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11. way 1: Classic
• Skin circulation heart lungs throat
swallowed intestine ( heart lung migration).
Way 2:direct
• L3 from the skin can migrate directly to via connective tissues and
reach the intestine (no heart lung migration).
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12. • Then L3 invade the epithelial cells of the small intestine
• Then they molt twice (L4 L5) and then grow to worms
• within 2-4 weeks the worms mature into male and female.
• After mating, the female worms lay the eggs in the mucosa.
• The eggs hatch immediately in mucosa into larvae.
• larvae migrate into the lumen of the intestine ready to pass with stool.
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13. What is going on in man
intestine??
• worms are found in mucosa
• They lay eggs containing larva
• Eggs hatch immediately
• The larva migrate from mucosa
to the intestinal lumen
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14. How the cycle continue?
• When soil become contaminated with infected human feces containing (L2)
• In soil (L2) larva develop into larva (L3) under certain conditions: Shade,
Moisture ,Water, Warm Temperature
• n
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15. (2) Free living cycle (direct cycle):
• Similar to parasitic cycle but this occur in soil
L3 L4 L5 mature male &female worms mating
eggs in soil L1 L2 L3
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18. Pathology & Symptomatology
1-Skin phase:
Dermatitis; An itchy, red rash that occurs where the larva entered
the skin, creeping eruption may also occur.
2-Respiratory phase:
Löffler's syndrome (pneumonitis + Asma)
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19. 3-Abdominal phase:
• Infection may be asymptomatic(light infection)
• Symptoms resemble gastric ulcer; (stomachache, bloating,
and heartburn, hunger pain
• Chronic intermittent diarrhea may be with yellow mucus.
• Constipation
• Nausea and loss of appetite
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20. Complications
• Gasrtic ulcer resulting from damaged mucosa by the worms
• Intestinl obstruction occur In severe cases, edema may result in
obstruction of the intestinal tract, as well as loss of peristaltic
contractions.
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21. Who at risk?
• Strongyloidiasis in immunocompetent individuals is usually an
indolent disease.
• Has worse complications in immunocompromised individuals such as:
Human T-lymphotropic virus 1 and HIV patients
• Also patients under immunosuppressive drugs; corticosteroids and
agents used for tissue transplantation
• 90 % of those patients die as result of (Autoinfection, Hyperinfection,
or disseminated infection)
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22. 1-Autoinfection
• Occur when the larvae develop into L3 larvae in the intestinal lumen.
• Then larva penetrate the intestinal mucosa, enter the circulation (heart
lung migration) then return to the intestine & mature to adult worms.
• Result in increased number of worm & larva produced in the intestine
• Repeating of this cycle will lead to hyper-infection syndrome.
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23. 2-Hyper- infection syndrome:
• In hyperinfection syndrome, is
massive multiplication of the
parasite in the intestine through
(autoinfection)
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25. 4-Death:
• In hyper-infection syndrome; death occur due to massive invasion
of lungs by the larva which causes respiratory failure.
• In disseminated death occur due to invasion of vital organs by
larva; central nervous system which cause, brain infarction,
meningitis
• Septicemia & sepsis due to enteric bacteria which introduced into
blood and other organs by migrating larva form intestine.
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26. Difference of this worm from the other soil transmitted worm:
• Has 2 types of life cycle (parasitic & free-living)
• Has 2 ways to reach the intestine
• They develop into worm within the intestinal mucosa not the lumen.
• They lay the eggs within the mucosa of intestine not the lumen.
• Eggs hatch to larva also within the mucosa
• The larva(L2) can develop into infective L3 in the intestine.
• Can cause autoinfection
• Can cause hyper infection syndrome
• Disseminated infection
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27. Laboratory Diagnosis
1- what is /are suitable sample/s?
2- what is are suitable diagnostic test/s or technique/s?
3- what is/are the diagnostic stage/s?
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28. Summary:
• Strongyloides stercoralis worm inhabit the mucosa of human upper part
of small intestine (duodenum &jejunum)
• The worms and eggs occur in the intestinal mucosa; they can’t be found
stool.
• The only stage that found in stool is larva
• The larva found in feces but they may be (Few or many)
• Usually immunocompetant pass few larva, while immunocompromised
patients pass massive larva.
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29. 1-How to select the proper sample for the diagnosis?
RULE (1): If the parasite inhabit or released in the upper small intestine
(duodenal aspirate and stool) are suitable samples.
1-Stool & duodenal aspirate are both suitable to detect the larva of S.
stercoralis.
2- Duodenal aspiration is not preferable because:
• Require patient preparation
• Require special equipment's
• Require specialized physician
• It cost money & time
• Invasive procedure
• Require surgery or endoscopy
• Require anesthesia
• Complication after procedure
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30. 2-How to select the suitable diagnostic test?
RULE (2) : Selection of the suitable test depends on parasite number in
sample
If parasite produced in large
number;
• Direct sample examination is
adequate (wet prep)
If the parasite is few;
• Concentration technique
• Immunological tests
• Molecular tests
• Culture
• Special test
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32. 1-Baermann technique
Is a special concentration technique for
Strongyloides larva from fecal samples.
Principle:
The Baermann technique is based on the active
migration or movement of larvae from feces into
warm water (thermophilic & hydrophilic).
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34. procedure
• 5-10 gram fecal sample is placed
sieve.
• Covered with warm water about
40ᵒC
• Incubation for 1.5- 2 hours at least
• during incubation the larvae will
migrate out from feces into warm
water
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35. • The water is then collected,
• centrifuged
• Examined by microscope (deposit)
for motile larva
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36. 2-Water emergence technique
Based on the same principle of Baermann’s
technique, but it is much simple,
• instruct the patient to collect fresh stool
specimen
• make a hole in the center of the specimen
(use wooden stick)
• Fill the hole with warm water
• Incubate for 1.5 -2 hours at 40ᵒ C
• Collect the water , examine directly or after
centrifugation.
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37. Immunological tests:
• For detection of antibody in the patient serum (IgG)
• The antigens prepared from Strongyloides stercoralis filariform larvae for
the highest sensitivity and specificity.
• several test are avilable indirect fluorescent antibody (IFA) and indirect
hemagglutination (IHA) tests have been used, enzyme immunoassay (EIA).
• Enzyme immunoassay (EIA) is currently recommended because of its
greater sensitivity (90%).
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38. Treatment
Several anthelmintic drugs of choice:
• Thiabendazole
Prognosis
The prognosis is good except in disseminated or hyperinfection
syndrome
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