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45 Cards in this Set

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Common nematodes (roundworms) that infect humans include:(7)
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
Nematodes do not need an intermediate host in their life cycle, but ___
They require a stage outside of the human host for the ova to develop into the infective form
Ascariasis affects about ___ people worldwide
1 Billion (about 25% of the population [old stats])
Laboratory identification of Ascaris lumbricoides infection is via __
1. See the adult worms
2. See ova in stool specimens
Key features of the adult ascarid include:
1. 15-35 cm in length (big)
2. Smooth cuticle
Key features of ascarid eggs include:
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)
Detection of only unfertilized ascarid eggs in a stool specimen may indicate __
Infection by a single adult female ascarid
Do egg counts in stool specimens correlate with the severity of infection?

A single adult female ascarid can lay 200,000 eggs/day! (contrast to hookworm egg counts which are useful)
The life cycle of Ascaris lumbricoides includes:
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

Light Ascaris infection versus a heavy infection
Light: often asymptomatic

Heavy: abdominal pain, discomfort, and diarrhea
Is the presence of one ascarid significant?

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
Life cycle of Trichuris trichuria includes:
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)

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

Thin cephalic ends within the bowel wall and the thicker tails in the lumen
Light infections with Trichuris trichuria is typically ___,while heavy infections can cause ___ largely due to __
1. Asymptomatic
2. Diarrheal disease (dysentery)
3. Mechanical damage to the intestinal mucosa
A severe complication of Trichuris trichuria infection in children
Coconut cake prolapse - rectal prolapse with visible adult worms
Laboratory diagnosis of Trichuris trichuria is by __
Detection of barrel-shaped ova in fecal specimens

Adults are rarely seen in fecal specimens (they have their heads buried into the colonic mucosa)
Features of adult Trichuris trichuria
20-50 mm long (small)
Male has a coiled tail
(color plate 22-5E)
Features of Trichuris trichuria eggs
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)
Enterobius vermicularis (pinworm) is transmitted via __
Fecal-oral route (finger-to-mouth, human-to-human)
In fecal specimens, are pinworm eggs typically seen?
No! The mature to quickly. You can find them via tape prep
Diagnosis of enterobiasis is made by __
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
Best time to detect enterobiasis
early morning prior to cleaning and bowel movements
Where in the intestine do adult pinworms live?
Colon (cecum and rectum)
Signs and symptoms of enterobiasis include:
1. Nocturnal pruritus ani
2. Nervousness
3. Insomnia
4. Nightmares
5. Enuresis
Features of the adult pinworm include
1. Cuticular, perioral alae
2. Long pointed pin-like tail
(color plate 22-5G)
Features of the pinworm egg include
1. Thin, smooth, transparent shell that is flattened on one side
2. Presence of a well-developed larva
(color plate 22-5F)
The two hookworm species that infect humans are
Old world hookworm (Ancylostoma duodenale)

New world hookworm (Necator americanus)
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?
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!!
Hookworms infect about___ people worldwide
700-900 Million people (mostly A. duodenale)
Hookworm life cycle includes:
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

Symptoms of hookworm infection are related to stage of infection
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)
Hookworm egg quantification is useful?
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
How big are adult hookworms?

How are adult N. americanus and A. duodenale worms differentiated?
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)
Features of hookworm eggs
1. Oval
2. Thin, smooth, transparent shell
3. Space between the yolk cells and the shell
(color plate 22-5K)
The rhabditiform larvae of hookworms are uncommonly seen in ___
Fecal specimens (contrast with Strongyloides)
How can you distinguish the rhabditiform larvae of hookworms from those of Strongyloide stercoralis?
Hookworm rhabditiform larvae - long buccal cavity and small genital primordium

Strongyloides rhabditiform larvae - short buccal mucosa and prominent genital primordia

(color plate 22-5L)
The prevalence of strongyloidiasis is ___ to that of hookworm infections
In the US, strongyloidiasis is endemic in __
the rural south and southeast
Chronic strongyloidiasis is often associated with a ___ worm burden

Examination of multiple fecal specimens may be required to make or rule out the diagnosis
The life cycle of Strongyloides is similar to that of ___ except for
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)

Signs and symptoms of strongyloidiasis vary with the stage of infection
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
Ruling out strongyloidiasis in endemic areas prior to immunosuppressive therapy is important
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
Capillariasis (Capillaria philipinensis) is an uncommon infection acquired by __
Ingesting undercooked/raw fish
The eggs of Capillaria philipinensis must be distinguished from those of___
Trichuris trichuria

Capillaria eggs are more flattened, have a striated thick shell, and less conspicuous plugs
(color plate 22-5P)
Where in the intestine do the adult nematodes live?
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

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