Intestinal Nematodes Flashcards
Intestinal Nematodes
Known as Roundworms
Adult worms are long lived and survive in years
Anterior end has adaptations for attachment
Adult worms are both sexes
Males are usually smaller than female
Female may produce from few to 200,000 eggs/day
5 successive stages - four larval and adult worm
Most cases, 3rd stage larva is infective stage
Ascaris lumbricoides (large intestinal roundworm) General Information
Distributed worldwide in moist, warm climates, tropics and subtropics
Transmitted through ingestion of embryonated eggs from contaminated soil
Using human feces for fertilization of crops
Lifecylce of Ascaris lumbricoides
1) Eggs are ingested
2) Larvae hatch in duodenum (small intestine)
3) Larvae migrate to bronchial epithelium and cause damage
4) Larvae breakout into alveolar spaces
5) Larvae migrate up trachea and are swallowed
6) Adults mature in small intestine
7) Unembryonated eggs pass out in feces
Ascaris lumbricoides Adult Worm
Adults are white with thick cuticle that may become yellow from bile staining
Female:
- 20-35 cm long
- 5 mm in diameter
Male:
- 15-31 cm long
- More slender than female
- Curved Tail
Ascaris lumbroides Fertilized Egg
- Round to Oval
- 55-75 um x 35-50 um
- Outer, Bile Stained, Albuminous coat
- Thick Inner Hyaline Shell
- Unsegmented Ovum when passed
- Absence of fertile eggs means only females are present
Ascaris lumbricoides Unfertilized Egg
- Barrel Shaped
- 90-95 um x 43-47 um
- Thinner and often indistinct
- Mammillated layer varies from grossly irregular to relatively smooth
- Internal contents are mass of disorganized, highly refractive granules
Ascaris lumbricoides Pathology
Dyspnea
Dry or productive cough
Wheezing or coarse rales
Fever
Transient eosinophilia
Itching of throat and chest
Ascaris lumbricoides Diagnostic Stage
1) Larval migration phase - larvae seen in sputum or gastic washings
2) Intestinal phase:
- Eggs or Adult worms in stool (fertile or infertile)
- Direct Wet Prep or Concentration
Ascaris lumbricoides Infectious Stage
Eggs
Enterobius vermicularis General Characteristics
Organism is cosmopolitan in distribution
More prevalent in temperate, cool climates
High prevalence in children
Enterobius vermicularis Transmission
- Anus to mouth contamination, especially in children
- Soiled night clothes and towels
- Airborne eggs
- Contaminated furniture, toys, and other objects
Enterobius vermicularis Life Cycle
1) Eggs are ingested
2) Larvae hatch in small intestine
3) Larvae migrate to colon
4) Adults mature in colon
5) Adults migrate out of anus
6) Adults lay eggs on perineum
7) Eggs embryonate on perineum
8) Eggs contaminate fingers
Enterobius vermicularis Adult
Female:
- 10 x 0.4 mm
- Fusiform body with long, thin pointed tail
Male:
- 3 x 0.15 mm
- Curled tail with copulatory apparatus
Enterobius vermicularis Egg
- Oval, flattened on one side
- 50-60 um x 25 um
- Clear, colorless shell
- Thick walled
Enterobius vermicularis Pathology
- Slight irritation of intestinal mucosa
- Nausea
- Vomiting
- Diarrhea
- Pruritis (itching) caused by migration of female worm from anus to perianal region
Enterobius vermicularis Prevention
- Improved personal and group hygiene
- Children sleep in closed garments with short, clean fingernails
- Dry heat used to sterilize
Enterobius vermicularis Diagnostic Stage
1) Detect eggs and/or adult worms by scotch tape prep
- Collect first thing in morning prior to showering or going to bathroom
2) Minimum 4-6 tapes required to rule out infection
3) Less than 5% of infections show eggs in stool
Trichuris trichiura General Characteristics
- Distributed in tropics and subtropics
- Children frequently pick up organism from contaminated soil
Trichuris trichiura Life Cycle
1) Eggs are ingested
2) Larvae hatch in small intestines
3) Larvae migrate to colon
4) Adults mature in colon
5) Umembryonated eggs pass out in feces
6) Eggs embryonate in soil
Trichuris trichiura Adult
Adult form is rarely recovered from stool due to firmly attaching to intestinal wall
Female:
- 40 mm in length
- long, slender esophageal region
Male:
- Smaller
- Coiled tail and copulating apparatus
Trichuris trichiura egg
Barrel shape
50 um x 20 um
Bile stained
Have 2 shell membranes
Translucent polar plugs
Unsegmented ovum or embryo
Trichuris trichiura Pathology
Asymptomatic or Symptomatic
Abdmoninal pain
Vomiting
Constipation
Fever
Distention of stomach and intestines
Flatulence
Heavy infections: bloody diarrhea, emaciation, prolapsed rectum
Trichuris trichiura Diagnostic Stage
Recovery of eggs in direct wet prep or concentration
- Adult worms are rarely recovered
Hookwork Generic Information
Ancylostoma duodenale (Old Work) and Necator americanus (New World)
- More common in the tropics and subtropics
- Worldwide about 900 million people carry
Hookworm Life Cycle
1) Infection via filariform larvae from contaminated soil (larval migrans)
2) Migration via the lymphatics and blood stream to the heart and lungs
3) Penetrate the alveoli
4) Migrate up the trachea and are swallowed
5) Adult worm matures in the small intestines
6) Unembryonated eggs pass out in the feces
7) Eggs rapidly develop into rhabditiform larvae (hatch within 24-48 hrs)
8) Rhabditiform larvae molts twice to become filariform
Necator americanus (New World Hookworm) adult
1) Female: 10 mm long, head end curved dorsally in hooked position
2) Male: 7-11 mm, posterior end forms copulating bursae
- Attaches to intestinal mucosa by two cutting plates (part of mouth)
Ancylostoma duodenale (Old World) Hookworm adult
1) Female: head is not curved dorsally, slightly larger than Necator species
2) Male: smaller than female, terminates posteriorly with copulatory bursae
- Attaches to intestinal mucosa by a dual set of teeth
Hookwork eggs
- Eggs of two species are almost identical and not distinguishable
- Oval with broad round ends
- 40-70 um x 40 um
- Thin clear, colorless shell
- Clear space between developing embryo and thin shell
Hookworm larvae
- Long buccal cavity
- Indistinct genital primordium, small and indistinct
- Hour glass shaped esophugus
- Pointed tail
Hookworm Pathology
1) Pruritic dermatitis leading to vesicles due to larval skin penetration
2) Pneumonitis due to migration of larvae in lungs
3) Nonspecific gastrointestinal symptoms: intermittant abdominal pain, loss of appetite, and desire to eat soil (gephagy) due to presence of adults
- In acute phase: increased peripheral eosinophilia
- In chronic phase: develop Fe deficiency anemia
4) Hypoalbuminemia
5) Diarrhea with black to red stools
Hookworm Diagnostic Stage
1) Recover and identify eggs in feces (direct and concentrate sediment)
2) If stool remains unpreserved for over 24 hrs, larvae may be seen. Differentiate from Strongyloids species
Stronglyoides stercoralis General Information
- Organism distributed worldwide
- Prefers warm, moist climates due to greater fraility of filariform larvae
Strongyloides stercoralis Life Cycle
Very similar to Hookworm, except eggs hatch in intestines and the L2 larvae are passed in feces
Strongyloides stercoralis adult
1) Female: small, slender 2 mm
2) Male: thought to have extremely short life span and not observed in humans
Strongyloides stercoralis egg
1) 50 um x 32 um
2) Similar to but smaller than hookworm eggs
3) Ova cannot be distinguished from hookworm
4) Clear thin shell
5) May be seen in diarrhic stool
Strongyloides stercoralis Larvae
1) Develops into filariform larvae in soil
2) 700 um in length
3) Short buccal cavity
4) Prominent genital primordium
5) Notched tail
Strongyloides stercoralis Pathology
Three areas of primary involvement
- Cutaneous skin itching
- Lungs - dyspnea and malaise
- Intestinal - pain, nausea, vomiting, diarrhea
Autoinfecion - long term immunocompromised, pneumonitis, and eosinophilia
Strongyloides stercoralis Diagnostic Stage
- Recovery and identification of larval stages in feces
- Rarely see embryonated eggs in stool unless highly diarrhic stool
- String test has been used to recover this organism
Enterobius vermicularis Common name
Pinworm
Enterobius Infectious Stage
Eggs
Trichuris trichiura Common name
Whipworm
Trichuris trichiura Infectious Stage
Egg
Hookworm Infectious Stage
Filariform Larvae
Strongyloides stercoralis Infectious Stage
Filariform Larvae
