Intestinal Nematodes Flashcards
List the general characteristics of nematodes
- Nonsegmented
- Tapered at both ends
- Tough, protective coating of cuticle
- Separate sexes
- Fairly long-living (years)
- Diagnosis usually by finding eggs in feces
- Severity often related to the # of worms
Life cycle of nematodes
- Some have free-living form of larvae (rhabditiform larva) → infective form (filariform larva)
- Some can’t be free-living → infective stage is shed (person to person)
- No intermediate hosts (human is the definitive host for medically important roundworms)
Common name for Ascaris
None
Diagnostic form of Ascaris
Eggs
Infective form of Ascaris
Eggs ingested from soil, food, water
Which stage of the Ascaris life cycle is most commonly seen in the clinical specimen from an infected patient?
Adults can emerge from human nose, mouth, or anus
Clinical manifestation of Ascaris
- Sometimes asympatomatic
- Asthmatic (allergic rxn to parasite)
- Pneumonitis
- Bowel obstruction
- Adults may migrate to other tissues
Describe the microscopic appearance of Ascaris
- Oval eggs, often stain brown in stool
- Infertile eggs are elongated, bizarre shaped (no male present)
- Mammilated coat = lumpy bumpy
- Decorticated = lost coat
Common name for the Ancylostoma duodenale/Necator americanus
Hookworm
Diagnostic form of Ancylostoma duodenale/Necator americanus
Eggs, rhabditiform larvae
Infective form of Ancylostoma duodenale/Necator americanus
Filariform larvae
Which stage of Ancylostoma duodenale/Necator americanus is most commonly seen in clinical specimens from an infected patient?
Adult worms secrete anticoagulant and ingest blood → anemia
- Hemorrhages at site of attachment
Clinical manifestation of Ancylostoma duodenale/Necator americanus
- Bronchitis (large #s) but no sensitization like Ascaris
- Diarrhea, fever, nausea, vomiting
- Can cause mental/physical development impairment in children
Describe the microscopic appearance of Ancylostoma duodenale/Necator americanus
- Eggs in stool → oval, colorless, thin-shelled
- Filariform larvae → pointed tail
- Rhabditiform larvae → small genital primordium and longer buccal cavity
- Adult
Differentiate Ancylostoma and Necator in diganosis of hookworm adults
- Ancylostoma has two pairs of cutting teeth
- Necator has cutting plates
What intestinal nematode causes “creeping eruption”/”cutaneous larvae migrans” in humans?
Ancylostoma duodenale/Necator americanus
Clinical manifestation of “creeping eruption”
- Larvae migrate through subcutaneous tissues causing irritation
- Dog or cat hookworm
- Secondary infections
- Animals, beaches/sandboxes and bare feet
Common name for Strongyloides stercoralis
Threadworm
Diagnostic form of Strongyloides stercoralis
Rhabditiform, sometimes eggs
Infective form of Strongyloides stercoralis
Filariform
Which stage of Strongyloides stercoralis is most commonly seen in clinical specimens from an infected patient?
Rhabitiform larvae
Clinical manifestation of Strongyloides stercoralis
- Usually mild/no symptoms unless immunocompromised (disseminated strongyloidiasis or hyperinfection)
- Nausea, vomiting, sharp pains (ulceration)
- Rarely skin irritation at site of entry
- Non-bacterial pneumonia w/ eosinophilia, respiratory failure (immunocompromised patients)
Describe the microscopic appearance of Strongyloides stercolaris
- Eggs rarely seen in stool (resembles hookworm)!
- Rhabditiform larvae sometimes in stool; short buccal cavity, large genital primordium (SHORT AND SEXY)
- Use sedimentation technique
Common name for Enterobius vermicularis
Pinworm (sharply pointed tail of female)
Diagnostic form of Enterobius vermicularis
Eggs (no fecal specimens)
Infective form of Enterobius vermicularis
Eggs (no external maturation required)
Which stage of Enterobius vermicularis is most commonly seen in clinical specimens from an infected patient?
Eggs
Clinical manifestation of Enterobius vermicularis
- Often asymptomatic
- Anal itching (pruritus), loss of sleep
- May be loss of appetite, nausea, vomiting
Describe the microscopic appearance of Enterobius vermacularis
- Eggs = oval, slightly flattened, w/ thin, smooth, colorless shell; usually internal larvae can be seen
- Adult female = pointed tail (male tail is curved), alae (3 lips)
Common name for Trichuris trichiura
Whipworm
Diagnostic form of Trichuris trichiura
Eggs
Infective form of Trichuris trichiura
Eggs
Which stage of Trichuris trichiura is most commonly seen in clinical specimens from an infected patient?
Eggs passed in stool (occasionally adult)
Clinical manifestation of Trichuris trichiura
- Light infections may be asymptomatic
- Heavy infections: diarrhea, weight loss, pain, bleeding, anemia, PROLAPSED RECTUM in repeated infections
Describe the microscopic appearance of Trichuris trichiura
Barrel-shaped eggs, w/ polar plugs at each end, unembryonated
Common name for nematodes
Roundworms
Know the sizes of the eggs for each Nematode discussed
- Strongyloides stercolaris (40-85um)
- Ascaris (45-75um)
- Trichuris trichiura (50um)
- Hookworm (50-60um)
- Enterobius vermicularis (55um)
Arrange the adult nematode worms from smallest to largest in relative size
- Strongyloides stercolaris
- Enterobius vermicularis
- Hookworm
- Trichuris trichiura
- Ascaris
Describe the method of choice for obtaining pinworm specimens
Cellophane tape preparation or paddle
- When first wakening (before showering)
- Clear tape (not frosted) placed over end of tongue depressor (sticky side out)
- Perianal area touched with sticky tape, then tape stuck to slide
Widespread (warm climates, associated w/ poor sanitation
Ascaris
Which type of hookworm is still prevalent in rural areas of U.S. (Kentucky and South)
Necator americanus
Which nematode is associated w/ lung involvement?
- Hookworm
- Ascaris
- Strongyloides stercoralis
Which nematode is associated w/ ground itch at site of penetration?
Hookworm
Which Nematode is found in some areas of Appalachia or rural Southeastern U.S. and doesn’t need a host?
Strongyloides stercoralis
How do we get autoinfection in Strongyloides stercoralis?
Larvae penetrate intestine or perianal skin → circulation
The only organism that is agar plate cultured
Strongyloides stercoralis
Describe the Agar plate culture in Strongyloides stercoralis
- Stool is placed on agar plate
- Incubate @ RT for 2 days
- Larvae will migrate over agar, carrying bacteria, leaving visible tracks
- Wash plate with formalin & examine larvae for ID
Most common Nematode in the U.S
Enterobius vermicularis
This nematode mostly found in families or crowded conditions by inhalation or ingestion of eggs or retroinfection and children most often infected.
Enterobius vermicularis
This Nematode is found worldwide and southern U.S.
Trichuris trichiura
Which Nematode is associated w/ infections acquired through the skin?
- Hookworm
- Strongyloides stercolaris
Which Nematode is associated w/ “ground itch”?
Hookworm
Which Nematode is associated w/ anal pruritis?
Enterobius vermicularis
Which Nematode is associated w/ prolapsed rectum?
Trichuris trichiura
Which Nematode is associated w/ “creeping eruption” or cutaneous larvae migrans (CLM)?
Ancylostoma duodenale/Necator americanus
Which Nematode is associated w/ bowel obstruction?
Ascaris
Which Nematode is associated w/ anemia from adult worms excreting anticoagulant?
Ancylostoma duodenale/Necator americanus
Which Nematode is associated w/ appearance of adult from human mouth or nose?
Ascaris
Which Nematodes are seen in patients who have NOT been outside the U.S.
??
How is Ascaris acquired??
(D) Eggs passed → develop into infective stage (embryonated eggs) →(I) eggs ingested → hatch in intestine → larvae penetrate intestines → blood or lymphatics → liver, heart → filtered by lungs → esophagus (swallowed) → small intestine → mature to adults and lay eggs
How is Ancylostoma duodenale/Necator americanus acquired??
(D) Eggs passed → moist soil → (D) rhabditiform larvae → (I) filariform larvae → penetrate skin of humans (foot) or ingested → circulation → lung, trachae, esophagus (swallowed) → attachment in intestine → mature to adults that lay eggs
How is Strongyloides stercoralis acquired??
(D) Rhabditiform larvae passed in feces → adults produce eggs in soil → (I) filariform larvae penetrate skin → circulation → lung, trachae, esophagus (swallowed) → adults produce eggs in intestines → eggs hatch into rhabditiform larvae OR autoreinfection
How is Enterobius vermicularis acquired?
- Female migrates outside of anus at night to lay eggs
- Eggs are infective w/in hours (no external maturation required) → USE LAB CAUTION!
How is Trichuris trichiura acquire??
(D) Eggs passed → eggs embryonate in soil → (I) eggs ingested → larvae released in intestine → larvae mature to adult → adult female attaches to intestine and lays eggs
This Nematode has the thickness of a pencil; cuticle has circular striations and is creamy white
Ascaris
Since eggs and larvae of two genera are indistinguishable in hookworm, how can we report that?
Report as “hookworm”
Which form of Strongyloides stercoralis is seen in sputum in immunocompromised patients?
- Filariform larvae → notched tail; seen in sputum (immunocompromised patients)
