Strongyloides stercoralis

Parasitology presentation include: morphology, life cycle, pathology, lab diagnosis, prevention & control

1. Strongyloides stercoralis ( ( The Thread worm Lecture by: Maha Gamal Eldein Ali

2. Introduction Strongyloides stercoralis is a human parasitic roundworm, commonly known as threadworm . I nhabit 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. I t is most common in the tropics, subtropics regions. H as 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. 3

4. Morphology (worm & Larva) 4

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 5

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. 6

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 7

8. Types of esophagus in helminthes 8

9. life cycle: Has two types alternates between free-living and parasitic cycles ( hetrogenic ) 1- Parasitic cycle : O ccur in human (adult worm develop in man intestine) 2- free living cycle: Occur in soil (adult worm develop in soil) 9

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 10

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 ). 11

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. 12

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 13

14. How the cycle continue? When soil become contaminated with infected human feces containing (L2) I n soil (L2) larva develop into larva (L3) under certain conditions: Shade, Moisture ,Water, Warm Temperature n 14

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 15

16. Free living cycle 16

17. Life cycle 17

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 ) 18

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 N ausea and loss of appetite 19

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. 20

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 ) 21

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. 22

23. 2-Hyper- infection syndrome: In hyperinfection syndrome, is massive multiplication of the parasite in the intestine through (autoinfection ) 23

24. 3-Disseminated strongyloidiasis: In disseminated strongyloidiasis the larvae invade numerous organs; liver, heart, brain. 24

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. 25

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 26

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? 27

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 T he larva found in feces but they may be ( Few or many ) Usually immunocompetant pass few larva, while immunocompromised patients pass massive larva. 28

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. s tercoralis. 2- D uodenal 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 29

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 30

31. 2- Suitable diagnostic technique for S. stercoralis : 31

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). 32

33. The Bearmann apparatus consists of: 33

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 34

35. The water is then collected, centrifuged Examined by microscope (deposit) for motile larva 35

36. 2-Water emergence technique B ased 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. 36

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 i mmunoassay (EIA) is currently recommended because of its greater sensitivity (90 %). 37

38. Treatment Several anthelmintic drugs of choice: T hiabendazole Prognosis The prognosis is good except in disseminated or hyperinfection syndrome 38

39. Prevention & Control 39

40. Avoid contamination of soil with human feces: 1- Avoid defecation in soil 2-Construction latrines where people need. 40

41. 3 - Early diagnosis treatment of infected individual 4-Wear shoes when you are walking or working on soil 41