Week 4: Nematodes Flashcards
Where do nematodes typically infect?
Intestines
Blood and tissue
What are 3 main ways that nematodes are transmitted?
- Ingestion of embryonated eggs
- Direct penetration of skin by larvae
- Insect vector
From where do adult nematodes obtain food?
- Partially digested intestinal contents
- Ingesting blood
List intestinal nematodes
- Enterobius vermicularis (pinworm)
- Trichuris trichiura (whipworm)
- Ascaris lumbricoides (most common helminth infection)
- Necator americanus (hookworm)
- Ancylostoma duodenalae (hookworm)
- Strongyloides stercoralis (threadworm)
List blood and tissue nematodes
- Trichinella spiralis
- Dracunculus medinensis (Guinea worm)
- Filarial worms (there’s a bunch we need to know that I won’t include here to keep the flashcard shorter)
List clinically important microfilaria
- Wuchereria bancrofti
- Brugia malayi
- Loa loa
- Onchocerca volvulus
Describe the life cycle of Enterobius vermicularis (aka whipworm). Include infective and diagnostic stages
- Larvae inside eggs mature within 4-6 hrs. Located in perianal folds (is this the buttcrack??? I’m not googling this in class) Diagnostic stage
- Embryonated eggs ingested Infective stage
- Larvae hatch in small intestine
- Adults in lumen of cecum
- Gravid (female adult) migrates to perianal region at night to lay eggs
- Repeat cycle
Describe Enterobius vermicularis egg characteristics
- Size: 50-60 by 20-30 microns
- Thick, double-layered shell, flattened on one side
- Larvae may be visible inside
Describe the Trichuris trichiura (whipworm) lifecycle. Include infective and diagnostic stages
- Diagnostic stage: Unembryonated eggs passed in feces
- 2- cell stage
- Advanced cleavage
- Infective stage: Embryonated eggs are ingested
- Larvae hatch in small intestines
- Adults in cecum
- Repeat cycle
Which laboratory diagnostic method do you use for Trichuris trichiura?
FEA concentration because found in stool
Describe Trichuris trichiura unembryonated egg characteristics
- Size: 50-55 by 22-24 microns
- Barrel-shaped, bile stained, thick shell, mucoid plugs at each end
- You occasionally see adults in feces but mainly see egg stage
Describe the Ascaris lumbricoides life cycle. Include infective and diagnostic stages
- Diagnostic stage Adult worms in small intestine lay eggs that get passed in feces
- Infective stage: Fertilized eggs ingested
- Hatched larvae migrate and circulate to lungs
- coughed up and swallowed, so go to GI tract
- Repeat cycle
Why do these worms typically not cause symptoms? Mentioned in lecture, not in slides
- Load may not be high enough
- They’re happy enough to eat leftovers of what we humans eat
How do you diagnose Ascaris lumbricoides in the lab?
- Preserve whole worm in formalin or 70-90% ethanol
- Stool specimen for FEA concentration
- Wet mount to look for eggs
Describe Ascaris lumbricoides adults
- 6-12 inches in length
- Live in small intestines but do NOT attach
Describe Ascaris lumbricoides fertilized eggs
See image
Describe Ascaris lumbricoides unfertilized eggs
See image
Describe the Necator americanus and Ancylostoma duodenalae hookworm life cycles. Include infective and diagnostic stages
- Diagnostic stage: Eggs passed in feces
- Rhabditiform larva hatches
- Filariform larva form
- Infective stage: Filariform larva penetrates skin
- Adults in small intestines
How do you diagnose hookworm in the laboratory?
- Look for eggs in stool
- FEA concentration
Describe hookworm eggs
- Size: 60-75 by 35-40 microns
- Oval-shaped
- Smooth, thin shell
What kind of teeth Ancylostoma duodenale have?
Cutting teeth
What kind of teeth Necator americanus have?
Cutting plates
Describe the Strongyloides stercoralis threadworm life cycle. Include infective and diagnostic stages
This is too wordy to type out. Please look at picture :D
Infective stage: filariform larvae
Diagnostic stage: rhabditiform larvae in feces
How do you diagnose Strongyloides stercoralis in the lab?
ID rhabditiform larvae in feces, duodenal aspirate, or Entero-Test capsule
Describe Strongyloides stercoralis rhabditiform larvae
- Size: 200-300 microns long
How do you distinguish between Strongyloides and hookworm?
- Hookworm has longer buccal cavity
- Hookworm has absent genital primordium BUT it’s prominent in Strongyloides
- Tail of hookworm is pointed, but Strongyloides has notched tail
Not question, but review
:)
Describe the Trichinella spiralis life cycle. Include infective and diagnostic stages
Infective stage: encysted larvae in undercooked meat ingested
Diagnostic Stage: Larvae in striated muscle
What are the reservoir hosts for Trichinella spiralis?
Bears, rodents, and pigs!
How do you diagnose for Trichinella spiralis in the lab?
- Antibody detection (EIA)
- Muscle biopsy (pathology does this)
Describe the Dracunculus medinensis Guinea worm life cycle. Include infective and diagnostic stages
Infective stage: Larvae in copepod ingested through contaminated water
Diagnostic stage: Female emerging worm from skin; larvae escape blister and released into water
Describe the general filarial worm lifecycle. Include infective and diagnostic stages
Infective stage: Larvae in arthropod vector get passed to human through feeding site
Diagnostic stage: Microfilariae in blood/tissue (such as dermis)
How do you diagnose filarial worms in the lab?
- ID through stained blood smear
- ID in skin snip or tissue nodule
What type of disease manifestations are associated with Wuchureria bancroftii and Brugia malayi?
- Fever
- Lymphangitis (lymphatic channel inflammation)
- Elephantiasis
What type of disease manifestations are associated with Loa loa?
- Localized subcutaneous edema (aka Calabar swellings)
- Eyeworm
What type of disease manifestations are associated with Onchocerca volvulus?
- River blindness
- Fibrotic nodules on skin
Describe traits to look for in Wuchereria bancrofti (lymphatic)
- Sheath
- No nuclei in the tip of tail
Describe traits to look for in Brugi malayi (lymphatic)
- Sheath
- 2 distinct nuclei in the tip of the tail
Describe traits to look for in Loa loa (eye worm)
- Sheath
- Nuclei extending to the tip of the tail
Describe traits to look for in Onchocerca volvulus (skin)
-No sheath
- No nuclei in the tip of tail
Put it all together! What are the traits you look for in the different filiarial worms (sheath, nuclei)
:)
ID this intestinal nematode and stage
Enterobius vermicularis egg
ID this intestinal nematode and stage
Trichuris trichiura egg
ID this intestinal nematode and stage
Ascaris lumbricoides fertilized egg
ID this intestinal nematode and stage
Ascaris lumbricoides unfertilized egg
ID this intestinal nematode and stage
Hookworm egg
ID this intestinal nematode and stage
Strongyloides stercoralis rhabditiform larvae
ID this tissue nematode stage
Trichinella spiralis larvae
The pic is too gross to put here: but which blood/tissue nematode crawls out of your skin for the diagnostic stage?
Dracunculus medinensis
AKA Guinea worm
ID the following filarial worm
Wuchereria bancrofti
ID the following filarial worm
Brugia malayi
ID the following filarial worm
Loa loa
ID the following filarial worm
Loa loa
ID the following filarial worm
Onchocerca volvulus
