Bailey & Scott's Diagnostic Microbiology: Intestinal Nematodes Flashcards

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Nematodes (roundworms)

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


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

clinical presentation disease of roundworms


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


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


ascaris lumbricoides adult femal

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


ascaris lumbricoides adult male

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


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


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


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


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


Enterobius vermicularis female adult

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


Enterobius vermicularis male adult

up to 2.5 mm


Enterobius vermicularis ova

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


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


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


Strongyloides stercoralis parasitic cycle

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


Strongyloides stercoralis threadworm autoinfection

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


Strongyloides stercoralis threadworm hyperinfection

contributed by autoinfection; disseminated infection is severe form


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


Strongyloides stercoralis rhabditiform larvae morphology

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


Strongyloides stercoralis filariform larvae morphology

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


not generally seen in feces

segmented eggs of Strongyloides stercoralis


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


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


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


Trichuris trichiura- whipworm eggs

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


Trichuris trichiura- whipworm adult males

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


Trichuris trichiura- whipworm adult female

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


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


Capillaria philippinensis

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


Capillaria philippinensis clinical presentation

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


Capillaria philippinensis laboratory diagnosis

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


Ancylostoma duodenale

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


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



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


classic hookworm disease

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


cutaneous larva migrans

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


eosinophilic enteritis

Anculostoma caninum causes diarrhea and abdominal pain but no blood loss


hookworm eggs

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


hookworm rhabditiform larvae

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


hookworm filariform larvae

500-600 um long with pointed tails


hookworm laboratory diagnosis

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