Nematodes - Soil Transmitted Helminths Flashcards
What are the 3 most important STH infections?
- Trichuris 2. Ascaris 3. Hookworms (unholy trinity)
In which class is Trichuris trichiura found?
Enoplea
What is the common name of Trichuris trichiura?
whipworm
Why did Trichuris trichiura get its common name?
anterior end = slender & posterior end = thicker like a whip
How can the egg of Trichuris trichiura be recognized?
very thick shells & opercular knobs
What environmental conditions stimulate embryonation in Trichuris trichiura?
moisture, shade leads to L3
Does the egg hatch in the external environment in Trichuris trichiura?
no they hatch in small intestine
What happens when Trichuris trichiura gets into the host?
hatch in upper portions of SI & burrow into cells of intestinal villi where they mature
Where does Trichuris trichiura molt?
cells of the intestinal villi
Where do adult Trichuris trichiura worms live?
colon submucosa
How can male and female Trichuris trichiura worms be identified?
male has coiled posterior end
How do Trichuris trichiura worms cause hemorrhage and anemia?
~0.005mL blood/worm per day lost in stool. infection of 200 worms in a child -> increases daily iron needs by 4.25mg/day -> iron deficiency
How does Trichuris trichiura cause colitis?
inflammation of colon
What is TDS?
trichuris dysentery syndrome: severe diarrhea
What can happen if pertistalsis is overstimulated?
rectal prolapse
What types of systemic effects can occur as a result of infection with Trichuris?
- stunted growth 2. impared cognitive function 3. finger & toe clubbing
How is infection with Trichuris trichiura diagnosed?
eggs in feces
How is infection with Trichuris trichiura treated?
mebendazole & albendazole
Who is most likely to be infected with Trichuris?
children
Where in the world is Trichuris trichiura infection found?
tropical climates (south east USA)
What conditions increase the chance that Trichuris trichiura is present?
- warm climate 2. rainfall & humidity 3. moisture retaining soil 4. shade
In which class is Ascaris lumbricoides found?
Chromadorea
What is the origin of Ascaris lumbricoides’ egg’s mammillated covering?
proteinaceous layer (outermost) from uterine wall
Why is Ascaris lumbricoides’ egg golden brown?
absorbs host bile
Where are ascarosides found and what is their function?
sugar bound to non sugar by glycosidic bond makes eggshell impermeable to H2O soluble substances
What is the size of adult Ascaris lumbricoides males and females?
males: 30cmx3mm females: 35cmx5mm
How many lips do Ascaris lumbricoides have?
3
What stage of Ascaris lumbricoides is ingested by the human?
infective egg
Where does Ascaris lumbricoides molt inside the host?
2x in lungs and once in small intestine
Where is Ascaris hemoglobin found?
perieuteric - in fluid surrounding parasite intestine hemolymph
How many subunits are in a Ascaris Hb molecules
8 identical subunits & 16 hemes
How tightly does Ascaris Hb bind to O2 compared to human Hb?
25,000x greater affinity for O2 than human Hb. mammals have millisec off rate vs. ascaris taken several minutes
Describe the hypothesis which explains the affinity of Ascaris Hb to oxygen.
steral biosynthesis hypothesis: seteral - lipid is needed for worms egg production and lots of O2 is needed for this. intestine has a low O2 so it is important the Hb retains O2 in Ascaris
What are the 3 phases of Ascaris pathology?
- migration 2. pulmonary 3. intestinal (adults)
When would you expect to observe Loeffler’s syndrome?
pulmonary stage of Ascaris pathology: increase in eosinophils in lungs responding to protein on larval surface causes cough, wheezing, and chest pain
Where do adult Ascaris worms wander?
into pancreas or bile duct
How is infection with Ascaris diagnosed?
eggs in feces
How is infection with Ascaris treated?
albendenazole and mebendenazole, PZQ, piperzine
Where do Ascaris infections occur most frequently?
warmer climates/poor sanitation in children (“backyard infection)
How can infection of Ascaris be controlled?
- drug treatment 2. sanitation 3. no night soil 4. education
In which class are the hookworms found?
Secerneutea
How is the infection transmitted to the human host in hookworms?
skin penetration
Is there an IH in the hookworm life cycle?
no
How did hookworms get their common name?
skin penetration by larva
Do hookworms have a buccal cavity?
yes has teeth or cutting plates
What does the male hookworm do with the bursa?
holds onto female during mating
What conditions stimulate the hookworm egg to embryonate?
warm, moist, shady
Do hookworm eggs have a thick eggshell?
no: oval & very thin shell
Where do the hookworm L1 and L2 stages live and what do they do?
soil, feed on fecal material & grow & molt
Does the hookworm L3 feed?
no: transmission stage & lives in upper few cm of soil
What do hookworm L3s do when the soil is dry? When the soil is wet?
dry: move down into soil vs. wet: move up in soil
What are the 2 species of hookworms which most commonly infect humans? Compare distribution & buccal cavity morphology
- Necater americanus 2. Ancylostoma ducdenale
What is the distribution of Necater americanus & buccal cavity morphology?
Southeast USA. anterior has 4 cutting plates & posterior has 4 teeth
What is the distribution of Ancylostoma ducdenale & buccal cavity morphology?
Europe, Asia, Africa. anterior has 2 cutting plates, each plate has 2 teeth
What are the 3 phases of hookworm infection?
- invasion 2. migration 3. intestinal
What is ground itch?
local rash & irritation due to inflammatory rxn to bacteria
Where is the principal site of damage during the migration phase for hookworms?
lungs: L3 break out of capillaries in alveoli causes coughing, pneumonia
Why is the intestinal phase of hookworm infection the most serious?
adult worms in SI w/ cutting plates/teeth are burrowing into intestinal mucosa
How do hookworms maintain blood flow?
secrete salivary secretion w/ anticoagulants
What is the food resource of hookworms?
blood
What is hemoglobinolysis?
worms digest Hb
What enzymes are involved in hemoglobin digestion by hookworms?
- hemolysin 2. aspartic proteases & cystine proteases 3. metalloproteases 4. exopeptidases
What is cutaneous larva migrans and by what species is it most commonly caused?
skin disease in humans caused by nonhuman hookworms that wander in the skin most commonly caused by Ancylostoma brazilense & A. caninum (cat & dog hookworms)
What are the goals of Children without Worms program?
donate to national STH control programs
What is MDA?
mass drug administrations (albendenazole & mebendazole)
What is WASH?
- WAter (increase access to water for personal hygine & environmental sanitation) 2. Sanitation (reduce open defecation & latrines) 3. Hygine (hand & face washing, shoes)
Compare autoinfection, homogonic cycle, and heterogonic cycle.
autoinfection: life cycle of a parasite in one host vs. homogonic cycle: has a free living stage vs. heterogonic cycle: organism that has a parasitic stage
Under what conditions is heterogonic cycle most likely to occur?
unfavorable conditions
What sex of Strongyloides stercoralis is found inside the host ?
females
What does protandrous mean?
male reproductive organs come to maturity before the female
What is common name of infection with S. stercoralis?
threadworm infections
What are the 3 phases of pathology S. stercoralis pathology?
- cutaneous: ground itch 2. pulmonary: cough, tracheal irritation 3. intestinal: nausea, pain
How is immune status related to hyperinfection syndrome?
impaired host immunity leads to accelerated autoinfection with overwhelming # of migratory larvae & adults in SI -> disseminated & strangyloidiasis: larvae invade organs -> death rate approaches 90%
What can occur during disseminated strongyloidiasis?
larvae invade organs
How is strongyloidiasis diagnosed?
ELISA
How is S. stercoralis infection treated?
invermechin
What populations are most at risk for S. stercoralis infection?
people who come in contact with warm, moist soil
In which class is Enterobius vermicularis found?
secerneutea
How did Enterobius vermicularis get its common name?
pinworm because it looks like a pin
Is Enterobius vermicularis common? Has it been around for a long time?
yes: oldest and most common parasite in the New World
What are the alae in Enterobius vermicularis?
thickenings of cuticle at anterior end
How can you differentiate male and female Enterobius vermicularis worms?
female: posterior end very pointed vs. male: coiled posterior end
Where do adult Enterobius vermicularis worms live?
secum and colon
What stage of Enterobius vermicularis is ingested by the host?
infective eggs
What is retroinfection?
eggs hatch in perianal area and L1s go back into intestine
What is autoinfection?
host ingests eggs produced by worms in host’s body
What pathology can result from infection with a large number of Enterobius vermicularis worms?
1.damage w/i intestine or around anus -> inflammation & bacterial infection 2. irritability 3. sleeplessness
How is Enterobius vermicularis infection diagnosed?
scotch tape test
What is the characteristic morphology of Enterobius vermicularis eggs?
one side is flat the other is rounded
How is Enterobius vermicularis infection treated?
pyrautel
Who should be treated if one person in the household is infected with Enterobius vermicularis? Why?
everyone bc infection is passed very easily
What age group is Enterobius vermicularis infection most prevalent? Why?
children because there is a lot of contamination at day care
