1. Strongyloides Stercoralis
By Kim Harbal and Marcus Williamson

2. Taxonomy CLASS: SECERNENTEA SUBCLASS: RHABDITIA ORDER: RHABDITIDA
SUBORDER: RHABDITINA
SUPERFAMILY: RHABDITOIDEA
FAMILY: STRONGYLOIDIDAE

3. Where is this Parasite Found?
Tropical and Sub-tropcial regions
Temperate regions
Rural areas, institutional settings, and in lower socioeconomic groups
Mostly found in warm moist areas that favor the survival of the juvenile stages

4. Geographic Distribution
Currently, an estimated million people are infected worldwide in 70 countries
In the US: Appalachians, especially in eastern Tennessee, Kentucky, and West Virginia.
Internationally: Sub-Saharan Africa, South and Southeast Asia, Central America, and South America, and parts of Eastern Europe

5. Question #1
Name a state that has Strongyloides stercoralis?

6. Geographic Distribution

7. General Things to Know Commonly called a Threadworm
The smallest nematode parasites of humans
Most Strongyloides and their eggs are found in the soil
Infections are initiated when exposed skin contacts contaminated soil
Autoinfection commonly occurs allowing infection to persist for decades
More common in people who suffer from alcholism, who are caucasion, males, or have an occupation that involves soil contact
Not likely to be transmitted through water

8. Hosts Definitive Intermediate Hosts Humans Dogs Cats Other mammals
None
There are 38 species of threadworms found in sheep, swine, goat, ox, deer, camel, rabbit, primates, dogs, and cats

9. Question #2
How many species of Strongyloides are there?

10. Egg stage Eggs are about 50 um to 68 um long and 30 um by 34 um wide.
Females produce several dozen eggs and release them in to the gut lumen or submucosa
Not normally diagnostic because eggs hatch before exiting the human host

11. Rhabditiform larvae stage (L1)
Non infective stage
Size ranges from microns in length and 60 microns in diameter
Passed with feces

12. Rhabditiform larvae stage (L1)
Distinguishable characteristics
short buccal cavity
clear esophagus
prominent genital primordium

13. Rhabditiform Stage (cont’d)

14. Filariform Stage (L3) Reside in the small intestine of the host
They are about 650 microns long and 50 microns in length
Have a long esophagus
This is the infective stage of Strongyloidiasis

15. Filariform Stage (cont’d)
Have a long non bulbous esophagus of about 2/5 of the length of the body
Female filariform larvae are slender and faster moving than the rhabditiform stage
Male filariform larvae are not parasitic, only the females are
Filariform larvae penetrate the skin by releasing hydrolitic enzymes

16. Question #3
Name one of the three distinguishable characteristics of rhabditiform larvae from other species of nematodes?

17. Question #4
What larvae form is the infective stage?

18. Free living Females Have a rhabditiform esophagus
Females are about 1 mm in length by um wide
Contain embryonated eggs
Females have a vulva that is about equatorial
Females uteri contains more eggs than most parasitic females

19. Free living Males Have a rhabditiform esophagus
Males are up to 0.9 mm long and 40um to 50 um wide
Have two simple spicules and a gubernaculum
Their pointed tail is a curved ventrad

20. Parthenogenetic females
Parthenogenetic females reach a length of mm
1/3 of the worm is the esophagus
Inhabit crypts of the small intestines
Female is stout and has a vulva that is about equatorial
Vulva is in the posterior third of the body
The uteri carries only a few eggs at a time

21. Question #5
T/F The adult male is found in the definitive host.

23. Life Cycle
Adults lay eggs in the intestines within the definitive host
Rhabditiform larvae hatch from the eggs in the intestines
Three possibilities from here
Free living adult worms (Heterogonic)
Filariform larvae (Homogenic - Parasitic Generation)
Autoinfection

24. Free living adult worms (Heterogonic)
Rhabditiform larvae will be excreted in the stool
In this developmental option, the rhabditiform will molt four times and will either become a female or male adult worm
The free-living adults then mate and produce eggs
The rhabditiform larvae then hatch from the eggs
The larvae then can either produce a new generation of adults or become filariform larvae

25. Homogenic Life Cycle
Rhaabditiform larvae will be excreted in the stool
The rhabditiform larvae molt twice and develop into filariform larvae
No adult stages outside of host with this life cycle

26. Autoinfection
In this, the rhabditiform larvae develop into filariform larvae before they leave the hosts intestines
The filariform larvae then penetrate the intestinal mucosa or perianal skin
They then follow the life cycle in the host…to be explained next…

27. Parasite in the host
Now, the filariform larvae from each cycle enter the circulatory system and travel to the heart
They come out of the pulmonary artery and enter into the lungs
Penetrate the alveolar spaces and are carried to the trachea and pharynx, swallowed, and make there way to the small intestines
In the small intestines they molt twice and become adult female worms
By parthenogenesis they produce eggs, yielding rhabditiform larvae
The prepatent period lasts about 1 month
Possible cycles start over again
Parthenogenesis – growth and development of an embryo without fertilization of a male

28. Question #6
Name 1 of the 3 cycles that occurs with Strongyloides stercoralis?

29. Question #7
What larvae stage is excreted in the stool?

30. Transmission Through contaminated soil Autoinfection
Ingestion
Skin contact
Autoinfection
Transmammary infection (with dogs)
Presumably it can occur in humans

31. Symptoms
Most Strongyloides infections are asymptomatic and can survive decades undiagnosed
The longest documented asymptomatic infection was more than 65 years
Symptomatic infections typically manifest in gastrointestinal, pulmonary, and dermatologic systems
In immunocompromised persons, symptomatic infections can be devastating and carry a 60-85% mortality rate
Acute Infection
Chronic infection
Hyperinfection
Disseminated Infection

32. Types of Infections Acute Infection Chronic infection Hyperinfection
Symptoms occur after a few weeks whether it is a cough, abdominal pain, diarrhea, and/or anorexia.
Most likely detection of hundreds of larvae
Chronic infection
manifested by epigastric pain, recurrent hives (urticaria) and transient red lines on the skin that appear and move rapidly (larva currens) and sporadic diarrhea
Hyperinfection
Most patients that experience this are immunocompromised
Most likely from accelerated autoinfection
Large number of parasites present
Large numbers of larvae in stool and/or sputum
Disseminated Infection
Migration of larvae to organs beyond the range of the pulmonary autoinfective cycle

33. Gastrointestinal Symptoms
Bloating, distension
Diffuse abdominal pain
Diarrhea, typically nonbloody
Anorexia, weight loss, nausea
Malabsorption syndromes may occur in chronic infections

34. Question #8
T/F It can be transmitted by breast milk

35. Dermatologic Symptoms
Ground itch - Papulovesicular pruritic rash, usually on the feet
Cutaneous infection: Dermatitis is produced by migration of the infective juveniles through the skin
Petechial/purpuric rash (with disseminated disease)
Inflammation
Slight hemorrhage and swelling
Larva currens – Skin lesions, hives, or rash often on the trunk and buttocks (allergic response due to migrating larvae

36. Cardiopulmonary Symptoms
Wheezing or coughing
Mild to severe symptoms of pneumonia when worms are present in the lungs
Hyperinfection syndrome
massive proliferation of larval forms
Pulpatations
Atriofibrillations
Choking sensation

37. Diagnosis Examination of feces and duodenal contents
Finding rhabdiform or filariform larvae in a fresh stool
If not in a fresh stool, may be misdiagnosed as hookworm
Finding larvae in the sputum
Culture techniques
ELISA
Immunodiagnosis by indirect immunofluorescence
Antigen: whole Strongyloides ratti larvae

38. Question #9
Name a way the parasite can be diagnosed?

39. Culture Technique Fairly new technique
Movement of the larval forms can be seen
Bacterial colonies of normal oral flora are formed along the moving trail
Performed using a chocolate agar sputum culture

40. Treatment and Prevention
Thiamendazole
Keeps nematode larvae from growing into adult forms
Cambendazole
Ivermection – 100% effective for clearing Strongyloides infection with no side effects

41. Control Proper hygiene Do not allow infected hosts to breast feed
Do not walk barefoot in soil
In Hospitals
Make sure you wear clean masks, gloves, and aprons
Wash hands frequently

42. Question #10
What drug is 100% effective against Strongyloidiasis?

43. Question #11
Are you more likely to get Strongyloidiasis by swimming in a lake or walking barefoot in the woods?

44. Works cited
Schmidt, G., & Roberts, L. (2005). Foundations of Parasitology (7th ed.). New York, NY: McGraw-Hill
Schmidt, G.S., and L.S. Roberts Chapter 25. Order Rhabditata: Pioneering Parasites. in Foundations of Parasitology. Times Mirror/Mosby College Publishing. St. Louis pages.