Parasitology - Intestinal Nematodes

Front 1

Common nematodes (roundworms) that infect humans include:(7)

Back 1

1. Ascaris lumbricoides
2. Trichuris trichuria
3. Hookworms (Necator americanus and Ancylostoma duodenale)
4. Strongyloides stercoralis
5. Enterobius vermicularis
6. Capillaria philipinensis
7. Trichostongylus spp

Front 2

Nematodes do not need an intermediate host in their life cycle, but ___

Back 2

They require a stage outside of the human host for the ova to develop into the infective form

Front 3

Ascariasis affects about ___ people worldwide

Back 3

1 Billion (about 25% of the population [old stats])

Front 4

Laboratory identification of Ascaris lumbricoides infection is via __

Back 4

1. See the adult worms
2. See ova in stool specimens

Front 5

Key features of the adult ascarid include:

Back 5

1. 15-35 cm in length (big)
2. Smooth cuticle

Front 6

Key features of ascarid eggs include:

Back 6

1. Fertilized eggs are smaller than unfertilized eggs
2. Yellow-brown, oval or spherical, egg
3. Thick, transparent hyaline shell with an albuminous coat (corticated) or without coat (decorticated due to exposure to digestive enzymes)

Front 7

Detection of only unfertilized ascarid eggs in a stool specimen may indicate __

Back 7

Infection by a single adult female ascarid

Front 8

Do egg counts in stool specimens correlate with the severity of infection?

Back 8

NO!

A single adult female ascarid can lay 200,000 eggs/day! (contrast to hookworm egg counts which are useful)

Front 9

The life cycle of Ascaris lumbricoides includes:

Back 9

1. Ingestion of infective, embyronated eggs from contaminated food/water
2. Larvae hatch in small intestne
3. Transpulmonary migragtory phase via blood
4. Larvae enter alveoli - coughed up - swallowed
5. Larvae mature into adults that live the the lumen of the small intestine
6. Female ascarids deposit eggs into feces
7. Eggs passed into environment where they mature into infective eggs containing stage 2 larvae

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Front 10

Light Ascaris infection versus a heavy infection

Back 10

Light: often asymptomatic

Heavy: abdominal pain, discomfort, and diarrhea

Front 11

Is the presence of one ascarid significant?

Back 11

Yes!

Unlike hookworms, in which heavy worm load is required for disease, one ascarid can travel around and block a bile duct, pancreatic duct, or the lumen of the appendix

Front 12

Life cycle of Trichuris trichuria includes:

Back 12

1. Release of eggs into feces
2. Maturation of eggs, in the environment, to an infective stage
3. Ingestion of egg with hatching in the intestine
4. Larve penetrate the intestinal mucosa and develop into adults that live in colon (cecum)

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Front 13

Adult Trichuris trichuria live in the ___ with their __ in the lumen

Back 13

Cecum

Thin cephalic ends within the bowel wall and the thicker tails in the lumen

Front 14

Light infections with Trichuris trichuria is typically ___,while heavy infections can cause ___ largely due to __

Back 14

1. Asymptomatic
2. Diarrheal disease (dysentery)
3. Mechanical damage to the intestinal mucosa

Front 15

A severe complication of Trichuris trichuria infection in children

Back 15

Coconut cake prolapse - rectal prolapse with visible adult worms

Front 16

Laboratory diagnosis of Trichuris trichuria is by __

Back 16

Detection of barrel-shaped ova in fecal specimens

Adults are rarely seen in fecal specimens (they have their heads buried into the colonic mucosa)

Front 17

Features of adult Trichuris trichuria

Back 17

20-50 mm long (small)
Male has a coiled tail
(color plate 22-5E)

Front 18

Features of Trichuris trichuria eggs

Back 18

Have a distinct barrel shape (color plate 22-5F) with hyaline, polar plugs at either end

Must be distinguished from eggs of Capillaria philipinensis (color plate 22-5P)

Front 19

Enterobius vermicularis (pinworm) is transmitted via __

Back 19

Fecal-oral route (finger-to-mouth, human-to-human)

Front 20

In fecal specimens, are pinworm eggs typically seen?

Back 20

No! The mature to quickly. You can find them via tape prep

Front 21

Diagnosis of enterobiasis is made by __

Back 21

1. Detection of adult worms at the anal opening
2. Tape prep - see adult worms and eggs
3. Typically do NOT see eggs in fecal specimens

Front 22

Best time to detect enterobiasis

Back 22

early morning prior to cleaning and bowel movements

Front 23

Where in the intestine do adult pinworms live?

Back 23

Colon (cecum and rectum)

Front 24

Signs and symptoms of enterobiasis include:

Back 24

1. Nocturnal pruritus ani
2. Nervousness
3. Insomnia
4. Nightmares
5. Enuresis

Front 25

Features of the adult pinworm include

Back 25

1. Cuticular, perioral alae
2. Long pointed pin-like tail
(color plate 22-5G)

Front 26

Features of the pinworm egg include

Back 26

1. Thin, smooth, transparent shell that is flattened on one side
2. Presence of a well-developed larva
(color plate 22-5F)

Front 27

The two hookworm species that infect humans are

Back 27

Old world hookworm (Ancylostoma duodenale)

New world hookworm (Necator americanus)

Front 28

How do you distinquish the eggs of N. americanus from those of A. duodenale?

How do you distinguish hookworm eggs from those of Strongyloides stercoralis?

Back 28

1. You cannot distinguish the hookworm eggs.

2. You cannot distinguish hookworm eggs from those of Strongyloides eithe!

BUT! Strongyloides eggs are rarely seen in fecal specimens, because the hatch inside the intestine!!

Front 29

Hookworms infect about___ people worldwide

Back 29

700-900 Million people (mostly A. duodenale)

Front 30

Hookworm life cycle includes:

Back 30

1. Eggs deposited into feces
2. Eggs hatch in soil - rhabditiform larvae (free-living in soil)
3. Rhabditiform larvae develop into infective filariform larvae
4. Filariform larva penetrate skin of human (hands, feet,..)
5. Similar to ascarids - transpulmonary migratory phase!!
6. Larvae burrow into mucosa and mature to adults in the small intestine
7. Gravide females deposit eggs into feces

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Front 31

Symptoms of hookworm infection are related to stage of infection

Back 31

1. Dermatitis and skin infection due to cutaneous penetration and migration
(Ground itch - especially with nonhuman hookworm species)
2. With a heavy infecting load - can see Loeffler syndrome with eosinophilia
3. Heavy infection (500+ worms) can be associated with signficant anemia (worm feed on blood)

Front 32

Hookworm egg quantification is useful?

Back 32

Yes, unlike ascarid egg counts.

Hookworm females lay 2,500-5,000 eggs/day

>2000 eggs/mL feces (women/children) and >5000 eggs/mL feces (men) reflect number of adult hookworms and the severity of infection

Front 33

How big are adult hookworms?

How are adult N. americanus and A. duodenale worms differentiated?

Back 33

1. up to 1.5 cm long

2. Mouth parts:
- A. duodenale - two pairs of chitinous teeth
- N. americanus - a pair of cutting plates

Both are adapted for accessing blood supply
(color plate22-5I)

Front 34

Features of hookworm eggs

Back 34

1. Oval
2. Thin, smooth, transparent shell
3. Space between the yolk cells and the shell
(color plate 22-5K)

Front 35

The rhabditiform larvae of hookworms are uncommonly seen in ___

Back 35

Fecal specimens (contrast with Strongyloides)

Front 36

How can you distinguish the rhabditiform larvae of hookworms from those of Strongyloide stercoralis?

Back 36

Hookworm rhabditiform larvae - long buccal cavity and small genital primordium

Strongyloides rhabditiform larvae - short buccal mucosa and prominent genital primordia

(color plate 22-5L)

Front 37

The prevalence of strongyloidiasis is ___ to that of hookworm infections

Back 37

similar

Front 38

In the US, strongyloidiasis is endemic in __

Back 38

the rural south and southeast

Front 39

Chronic strongyloidiasis is often associated with a ___ worm burden

Back 39

Low!!

Examination of multiple fecal specimens may be required to make or rule out the diagnosis

Front 40

The life cycle of Strongyloides is similar to that of ___ except for

Back 40

Similar to hookworm, EXCEPT:
1. Strongyloides eggs hatch while still in the intestine
2. Rhabditiform larvae passed in the feces can live as free-living, reproducing adults in the soil that lay eggs that hatch more rhabditiform larvae OR rhabditiform larvae can develop directly into infective filariform larvae
3. Filariform larvae penetrate the skin of humans
4. Similar to ascarids and hookworms there is a transpulmonary migratory phase
5. Maturation to adults that live in the small intestine
6. Females deposit eggs in the mucosa (occaisonally in the feces)

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Front 41

Signs and symptoms of strongyloidiasis vary with the stage of infection

Back 41

1. Skin irritation is less severe compared to hookworm
2. Light infeciton - asymptomatic
3. Heavy infection - severe bowel disease
4.Loeffler's syndrome with heavy infective dose
5. Nonbacterial pneumonia can develop in immunosuppressed

Front 42

Ruling out strongyloidiasis in endemic areas prior to immunosuppressive therapy is important

Back 42

Risk of hyperinfection due to autoinfection

Rhabditiform larvae can mature into infective filariform larvae while still in the intestine and directly reinfect the host

Occurs with steroids and other immunosuppressive therapies

ALSO: this hyperinfeciton can develop in the setting an asymptomatic subclinical infection

Front 43

Capillariasis (Capillaria philipinensis) is an uncommon infection acquired by __

Back 43

Ingesting undercooked/raw fish

Front 44

The eggs of Capillaria philipinensis must be distinguished from those of___

Back 44

Trichuris trichuria

Capillaria eggs are more flattened, have a striated thick shell, and less conspicuous plugs
(color plate 22-5P)

Front 45

Where in the intestine do the adult nematodes live?

Back 45

SMALL INTESTINE:
1. Ascaris lumbricoides
2. Hookworms
3. Strongyloides stercoralis
Note: All of the ones that live in the small intestine, also, exhibit a transpulmonary migratory phase in their life cycle

COLON:
1. Pinworms (cecum and rectum)
2. Trichuris trichuria (cecum)