Bailey & Scott's Diagnostic Microbiology: Intestinal Nematodes Flashcards


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1

Nematodes (roundworms)

nonsegmented, elongated and cylindrical; separate sexes in adults; eggs found in stool; infective stages vary; eggs -> larvae -> adult

2

number of worms present, length of time, and overall health

clinical presentation disease of roundworms

3

Ascaris lumbricoides

most common and largest roundworm; distributed worldwide- higher in tropics; transmitted by fecal-oral, dirty hands, or dirt; eggs ingested and hatched in duodenum; adults live in small intestine; can migrate to lungs, get coughed up, and swallowed

4

Ascaris lumbricoides clinical presentation

usually asymptomatic, generally mild and self-limiting; high worm burdens cause abdominal pain and intestinal obstruction; migrating adults can cause symptomatic occlusion of biliary tract or oral expulsion-ectopic ascariasis; pulmonary symptoms can occur during lung phase of larval migration

5

ascaris lumbricoides adult femal

20-35 cm long with straightened tail; have three lips at the anterior end of the body

6

ascaris lumbricoides adult male

males are 15-31 cm with curved tail; have three lips at the anterior end of the body

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ascaris lumbricoides ova

mammillated with outer casing or non-mammillated (decorticated); infertile eggs are oval or irregular shaped with a thin shell; fertile eggs are 45-75 um in length with a thick shell

8

Ascaris lumbricoides diagnosis

concentration technique for microscopic identification of eggs in feces, adult worm may be present; flotation is unacceptable-eggs are dense; expectorated sputum-adult worms may migrate to mouth or nares

9

Enterobius vermicularis

found worldwide in temperate zones; females migrate out of anus at night and lay eggs; transmission occurs by ingestion or inhalation of eggs (retroinfection); symptomatic perianal itching

10

Enterobius vermicularis clinical presentation

more prevalent in children up to 14 years of age; mild to self-limiting; perianal nocturnal itching; worm may enter appendix; reinfection- autoinfection acquired from fomites, retroinfection aquired from eggs hatch and larvae returning to intestine

11

Enterobius vermicularis female adult

8-13 mm has a pin-shaped tale; gravid are completely filled with eggs

12

Enterobius vermicularis male adult

up to 2.5 mm

13

Enterobius vermicularis ova

measure 50-60 um by 20-30 um; elongate-oval and slightly flattened on one side; eggs collected using tape

14

Enterobius vermicularis lab diagnosis

scotch tape prep or paddle of perianal region; collect flattened eggs for microscopic exam; occasional worm may be identified, gravid females filled with eggs

15

Strongyloides stercoralis free living soil

direct: Rhabtidiform larvae -> filariform larvae -> skin penetration; indirect: Rhabtidiform larvae in stool -> adult male and female -> embryonated eggs -> rhabtidiform larvae -> filariform larvae -> skin penetration

16

Strongyloides stercoralis parasitic cycle

filariform larvae -> skin -> heart -> lungs -> alveoli -> swallow sputum -> GI tract; adult female -> eggs via pathogenesis -> rhabtidiform larvae

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Strongyloides stercoralis threadworm autoinfection

Rhabtidiform larvae can transform into filariform larvae in the distal colon; filariform larvae infects colon mucosa or perianal area

18

Strongyloides stercoralis threadworm hyperinfection

contributed by autoinfection; disseminated infection is severe form

19

Strongyloides stercoralis-threadworm clinical presentation

asymptomatic with intermittent or chronic diarrhea and occasional abdominal pain; cough, wheezing, or dyspnea; pruritis, serpiginous or erythematous rashes; disseminated strongyloidiasis in immunosuppressed patients-eosinophelia, hyperinfection syndrome, penetration of the bowel, gram negative septicemia, and larcal migration to CNS, peritoneum, kidneys or liver

20

Strongyloides stercoralis rhabditiform larvae morphology

180-380 um; short buccal capsule, large bulb on esophagus, prominent genital primordium; diagnostic stage

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Strongyloides stercoralis filariform larvae morphology

600 um with notched tail; 1:1 esophageal-intestinal ratio; infective stage

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not generally seen in feces

segmented eggs of Strongyloides stercoralis

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Strongyloides stercoralis threadworm laboratory diagnosis

larvae found in the feces; demonstrating antibodies in the blood/supports diagnosis and may be used to monitor treatment; eosinophilia common during acute infection, but intermittent during chronic

24

Trichuris trichiura- whipworm

distributed worldwide, warm climate; no tissue migration; acquired via ingestion-eggs ingested, larvae mature in intestine, and eggs passed in feces; worms burrow into intestinal mucosa and feed on tissue secretions

25

Trichuris trichiura- whipworm clinical presentation

dependent on worm burden; light infections are asymptomatic or present with mild GI symptoms; epigastric pain, distension, and anorexia and weight loss with heavy infections; dysentery syndrome may occur; rectal prolapse possible in extreme cases

26

Trichuris trichiura- whipworm eggs

50-55 um by 20-25 um barrel or football-shaped, thick shelled with polar plugs

27

Trichuris trichiura- whipworm adult males

30-45 mm long with coiled posterior and long-whip-like anterior end

28

Trichuris trichiura- whipworm adult female

35-50 mm with straight posterior and long whip-like anterior end

29

Trichuris trichiura- whipworm lab diagnosis

microscopic examination of feces; eggs quantitated as rare, few, moderate, many; light infections do not generally require therapy; PVA eggs do not concentrate as well as in formalin

30

Capillaria philippinensis

prevalent in the Phillipines; transmitted by ingestion of uncooked fish; larvae burrow into GI mucosa, causing weight loss

31

Capillaria philippinensis clinical presentation

abdominal pain and diarrhea, autoinfection, protein loss, long-term infections may result in death due to protein loss

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Capillaria philippinensis laboratory diagnosis

eggs, worms, larvae identified in stool; eggs resemble T. trichiura, thick and thin shelled eggs

33

Ancylostoma duodenale

old world hookworm endemic to southern Europe, northern Africa, Southeast Asia, and South America; attached to mucosa by well developed mouthparts

34

Necator americanus

new world hookworm endemic to Africa, Southeast Asia, South and Central America, SE United States; attached to mucosa by well developed cutting plates

35

hookworms

filariform larvae penetrate the skin; larvae migrate to the lungs where they are swallowed, attach to GI mucosa and ingest blood; eggs passed in feces (diagnostic stage), release rhabditiform larvae and mature into filariform larvae (infective stage); infections related to poor sewage disposal

36

classic hookworm disease

Nectar americanus and Ancylostoma duodenale cause chronic blood loss leads to iron deficiency anemia and protein malnutrition

37

cutaneous larva migrans

Ancylostoma braziliense causes skin irritation leading to serpiginous tracks on the skin

38

eosinophilic enteritis

Anculostoma caninum causes diarrhea and abdominal pain but no blood loss

39

hookworm eggs

60-75 um by 35-40 um thin-shelled, colorles; 4-8 celled embryo; clear zone separates shell and embryo

40

hookworm rhabditiform larvae

250-300 um long with a long buccal capsule and small genital primordium

41

hookworm filariform larvae

500-600 um long with pointed tails

42

hookworm laboratory diagnosis

eggs or rhabditiform larvae (rare) found in stool; larvae identified in expectorated stool