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45 Cards in this Set
- Front
- Back
Common nematodes (roundworms) that infect humans include:(7)
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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 |
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Nematodes do not need an intermediate host in their life cycle, but ___
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They require a stage outside of the human host for the ova to develop into the infective form
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Ascariasis affects about ___ people worldwide
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1 Billion (about 25% of the population [old stats])
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Laboratory identification of Ascaris lumbricoides infection is via __
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1. See the adult worms
2. See ova in stool specimens |
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Key features of the adult ascarid include:
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1. 15-35 cm in length (big)
2. Smooth cuticle |
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Key features of ascarid eggs include:
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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) |
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Detection of only unfertilized ascarid eggs in a stool specimen may indicate __
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Infection by a single adult female ascarid
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Do egg counts in stool specimens correlate with the severity of infection?
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NO!
A single adult female ascarid can lay 200,000 eggs/day! (contrast to hookworm egg counts which are useful) |
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The life cycle of Ascaris lumbricoides includes:
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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 p.1275 |
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Light Ascaris infection versus a heavy infection
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Light: often asymptomatic
Heavy: abdominal pain, discomfort, and diarrhea |
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Is the presence of one ascarid significant?
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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 |
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Life cycle of Trichuris trichuria includes:
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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) p.1277 |
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Adult Trichuris trichuria live in the ___ with their __ in the lumen
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Cecum
Thin cephalic ends within the bowel wall and the thicker tails in the lumen |
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Light infections with Trichuris trichuria is typically ___,while heavy infections can cause ___ largely due to __
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1. Asymptomatic
2. Diarrheal disease (dysentery) 3. Mechanical damage to the intestinal mucosa |
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A severe complication of Trichuris trichuria infection in children
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Coconut cake prolapse - rectal prolapse with visible adult worms
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Laboratory diagnosis of Trichuris trichuria is by __
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Detection of barrel-shaped ova in fecal specimens
Adults are rarely seen in fecal specimens (they have their heads buried into the colonic mucosa) |
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Features of adult Trichuris trichuria
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20-50 mm long (small)
Male has a coiled tail (color plate 22-5E) |
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Features of Trichuris trichuria eggs
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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) |
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Enterobius vermicularis (pinworm) is transmitted via __
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Fecal-oral route (finger-to-mouth, human-to-human)
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In fecal specimens, are pinworm eggs typically seen?
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No! The mature to quickly. You can find them via tape prep
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Diagnosis of enterobiasis is made by __
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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 |
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Best time to detect enterobiasis
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early morning prior to cleaning and bowel movements
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Where in the intestine do adult pinworms live?
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Colon (cecum and rectum)
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Signs and symptoms of enterobiasis include:
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1. Nocturnal pruritus ani
2. Nervousness 3. Insomnia 4. Nightmares 5. Enuresis |
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Features of the adult pinworm include
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1. Cuticular, perioral alae
2. Long pointed pin-like tail (color plate 22-5G) |
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Features of the pinworm egg include
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1. Thin, smooth, transparent shell that is flattened on one side
2. Presence of a well-developed larva (color plate 22-5F) |
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The two hookworm species that infect humans are
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Old world hookworm (Ancylostoma duodenale)
New world hookworm (Necator americanus) |
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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!! |
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Hookworms infect about___ people worldwide
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700-900 Million people (mostly A. duodenale)
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Hookworm life cycle includes:
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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 p.1278 |
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Symptoms of hookworm infection are related to stage of infection
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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) |
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Hookworm egg quantification is useful?
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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 |
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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) |
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Features of hookworm eggs
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1. Oval
2. Thin, smooth, transparent shell 3. Space between the yolk cells and the shell (color plate 22-5K) |
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The rhabditiform larvae of hookworms are uncommonly seen in ___
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Fecal specimens (contrast with Strongyloides)
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How can you distinguish the rhabditiform larvae of hookworms from those of Strongyloide stercoralis?
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Hookworm rhabditiform larvae - long buccal cavity and small genital primordium
Strongyloides rhabditiform larvae - short buccal mucosa and prominent genital primordia (color plate 22-5L) |
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The prevalence of strongyloidiasis is ___ to that of hookworm infections
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similar
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In the US, strongyloidiasis is endemic in __
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the rural south and southeast
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Chronic strongyloidiasis is often associated with a ___ worm burden
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Low!!
Examination of multiple fecal specimens may be required to make or rule out the diagnosis |
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The life cycle of Strongyloides is similar to that of ___ except for
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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) p.1280 |
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Signs and symptoms of strongyloidiasis vary with the stage of infection
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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 |
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Ruling out strongyloidiasis in endemic areas prior to immunosuppressive therapy is important
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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 |
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Capillariasis (Capillaria philipinensis) is an uncommon infection acquired by __
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Ingesting undercooked/raw fish
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The eggs of Capillaria philipinensis must be distinguished from those of___
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Trichuris trichuria
Capillaria eggs are more flattened, have a striated thick shell, and less conspicuous plugs (color plate 22-5P) |
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Where in the intestine do the adult nematodes live?
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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) |