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58 Cards in this Set
- Front
- Back
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IMPORTANT: LIFE CYCLE
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REMEMBER THE LIFE CYCLE
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What is indicative of a helmith infection?
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High eosinophila rate
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How long can someone be infected with Strongyloides for?
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A very long time
Causes autoinfection. When you get the nematode, can have it for a long time, cuz the nematode decides if it wants to stay or leave |
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What causes Strongyloidiasis?
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Strongyloides stercoralis
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What kind of an infection is strongyloidiasis?
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4th most important nematode infection in the world
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What kind of disease does Strongyloides cause?
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Asymptomatic chronic disease of the GI tract for several decades
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What happens when this parasite infects immunocompromised patients and ppl who take corticosteroids?
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Gets disseminated
Mortality up to 85% |
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Describe the taxonomy of Strongyloides?
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Family: Strongylidae
Class: Secernentasida Order: Rhabditorida Genus: Strongyloides |
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Which Strongyloides species infects humans? Where?
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S. stecoralis **
S. fuelleborni in some parts of Africa (can also infect primates) |
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What are some other and what do they infect?
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S. ransomi: infects swine
S. papillosis: infects sheep |
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How many ppl are infected with strongyloides?
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100 million ppl worldwide
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Where is this helminth most problematic?
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Tropical and subtropical regions
Europe: Northern Italy, France, Spain, Switzerland, Poland) USA Japan Australia |
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How can you assess if someone is infected with this helminth?
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Check stool and blood samples
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What is the first stage juvenile (J1s) referred to as?
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Rhabditiform
-->Because posterior end and esophagus separated by a prominent buld |
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What are the 3 types of cycles Strongyloides can undergo in its life cycle?
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Autoinfection
Homogonic cycle Heterogonic cycle |
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What form of Strongyloides can actively infect ppl?
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Filariform juvenile
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Describe the life cycle of Strongyloides
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Filariform juvenile actively infects a person
Gets through the skin, goes directly to the heart and lungs After the 3rd molt, helminth passes up into the trachea and into the esophagus Juveniles migrate to the intestine where they develop into the adult female Female lays eggs which hatch in the intestine and the *L1* (rhabidiform) juveniles are released -->Have a choice to make |
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What happens after the L1 juveniles are released?
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Juveniles have a choice to make, depends on how many molts there are
--> If there are 2 molts, there can be autoinfection or the helminth can go through the homogonic cycle -->If there are 4 molts, can go through the heterogonic cycle |
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What happens in autoinfection?
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Juveniles do not leave the body
They penetrate the mucosa Then the juveniles enter the lymphatics or bloodstream and the cycle starts all over |
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What happens to the juveniles if they don't go into the autoinfection cycle?
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Juveniles pass into the soil with feces
Will go into the homogonic cycle or heterogonic cycle |
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What is required for the homogonic cycle?
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Start with 2 molts
In the soil, they eventually get to the filariform juvenile Then they penetrate the skin and the cycle starts over |
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What happens in the heterogonic cycle?
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After get into the soil, 2 molts can decide if they want to become filariform juvenile or if they want to become free-living male and female forms
-->Produce a rhabditiform juvenile that can become a filariform juvenile that can penetrate the skin and restart the cycle -->the rhabditiform juvenile can also produce 4 molts that undergo the heterogonic cycle |
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What stage is the filariform juvenile in?
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L3
-->L3 is the infective form (while L1 is the stage where parasite decides if it wants to stay in the body or go out) |
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What is a molt?
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The form when the parasite is changing btw generations
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What is bigger, the helminth male or female?
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The female is bigger and has many many eggs
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What happens during hyperinfection with this helminth?
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With immunosuppression, larger numbers of filariform larvae develop, penetrate bowel and disseminate causing: Colitis and Sepsis
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What happens during autoinfection?
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Parasite transforms within the intestine into the filariform larvae, which penetrate the perianal skin or bowel mucosa
Causes: Sepsis and Eosinophila |
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What happens during the lung and intestinal stages?
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Cause many lesions, sepsis
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What happens if ppl have a lot of larval migrants?
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Can cause lesions
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What is rather unique to Strongyloides?
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Has larval migrants, can see them in the blood
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What else is unique about Strongyloides?
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This nematode has free-living life cycle and an autoinfective cycle (in addition to the normal parasitic life cycle)
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What are the hosts for Strongyloides?
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Natural: Humans, other primates, dogs, cats
Experimentally: Gerbils, patas monkeys, SCID mice |
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How does this parasite reproduce?
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Parasitic adults are parthenogenic
Free-living adults are sexual |
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Where do the female strongyloides live?
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Small intestine, in the epithlial mucosa and crypts of Lieberkuhn
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What stage are the parasitic eggs in?
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L1
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What does the L3 do?
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Can actively penetrate the skin
Can cause autoinfection |
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What are triggers/inducing conditions for autoinfection?
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-Corticosteroids (prednisone)
-Immunosuppression (tacrolimus) -Neonatal infections -Infections with transplanted adults -Co-infection with Th1 inducing pathogens -Massive initial infections -Intestinal stasis |
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What determines homogonic vs heterogonic dev'p of the parasite?
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1) Immune status of the host
2) Env't parameters 3) Presence of food |
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What is the 3rd stage of infective larva?
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L3i
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What happens to the infective larva at the L3i stage?
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Positively thermotacic
Attracted to salt Increased movement in presence of CO2 Attracted to uronic acid Positively geotactic |
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What is the route of migration of this parasite throughout the body?
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-->Scramble hypothesis: any route that leads to the small intestine
-Migration starts with a layover in the skin (1-2) days + Migration from the skin (~4 days) = 5-6 days to reach the small intestine L4 stage = ~2days Young adults in intestine at 7 days post-infection L1 in feces (period pre-patent) by 10-14 days post infection |
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What does this parasite do to the GI?
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Epigastric abdominal pain
Postprandial fullness Heartburn Brief episodes of diarrhea Malabsorption |
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What does this parasite do to the pulmonary system?
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Diffuse broncopneumonia
Intra-alveolar hemorrhage |
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What are the cutaneous manifestations of this parasite?
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Urticarial rashes
Migratory serpiginous dermatitis Periumbilical cutaneous purpura |
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Where is the parasite prevalent?
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South America
Africa (esp Northern areas) Asia |
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What are the current diagnostic needs for strongyloides?
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Immigrant screening
Investigating peripheral eosinophilia Pre-immunosuppression screening HTLV-1 patient Strongyloides post-treatment follow-up Low cost, low-tech diagnosis in tropics |
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What are the diagnostic challenges of this parasite?
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Fatal disease in immunocompromised
Lifelong autoinfection Intermittent larval excretion Insensitivity of standard lab techniques Insensitivity of our best larva finding technique -->No available gold standard test Non-specificity of serological testing |
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What are some advances made in the past 30 years?
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Clarification of the insensitivity of the stool examination
ELISA with crude L3 Ag Agar plate method intoduced Work on population highly endemic for Strongyloides Intro and test recombinant Ag |
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What was the problem with the crude Ag?
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Wasn't specific
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What could then be used if ELISA wasn't working, since the crude Ag was not specific enoguh?
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NIE recombinant Ag
Somatic (crude) Ag |
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What are some sensitivity tests?
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Sera from stool positive cases diagnosed
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What are the advantages of specificity testing of strongyloides recombinant Ag serology?
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No endemic S. stercoralis
Plenty of trchinellosis in Arctic (non-travellers) Many other eosinophilic enteridides Some sylvatic hydatids Very rare human dirofilariasis |
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What are the disadvantages of specificity testing of strongyloides recombinant Ag serology?
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Souther Canada endemic for S. procyonis (in raccoon)
Other endemic Canadian helminths include: echinococcus granulosis, Toxocara canis, Baylisascaris procyonis, Diphyllobothrium spp |
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What is the most specific test?
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ELISA based on the NIE recombinant Ag is more sensitive then ELISAs based on other Ag
NIE Western Blot was more specific than the NIE ELISA |
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Is the NIE recombinant Ag safe?
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Yes, it is safe and reproducible
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How can this parasite be treated?
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Ivermectin: 200 ug/kg per day
Thiabendazole: 50mg/kg per day Albendazole: 400 mg orally for adults and 15 mg/kg per day for children |
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What is IL-5 important for?
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Recruitment of eosinophils
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What happens to ppl who are co-infected with the parasite and HTLV-1?
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They have more parasites in their stool
Have increased lvls of Tregs Decreased IL-5 response in co-infection |
