2. The nematode infection that may become more severe through ingestion of infective eggs, especially in infected infants, is:
a. Ancylostoma duodenale
b. Enterobius vermicularis
c. Strongyloides stercoralis
d. Trichinella spiralis
3. In the Ascaris lumbricoides life cycle, after eggs are ingested, the next stage in the life cycle that must occur before a mature adult can live in the host's intestine is called the:
a. Diagnostic stage
b. Infective stage
c. Liver-lung migration
d. Method of infection
4. Patients who have heavy infections with Necator americanus may exhibit all of the following symptoms EXCEPT:
a. Diarrhea
b. Larval dermatitis
c. Macrocytic anemia
d. Microcytic anemia
5. The nematode egg that appears as a barrel-shaped structure with clear polar plugs at each end of the egg belongs to:
a. Ascaris lumbricoides
b. Enterobius vermicularis
c. Strongyloides stercoralis
d. Trichuris trichiura
6. A slender round worm measuring 25 cm was recovered from a toilet following a child's trip to the bathroom. The specimen most likely is:
a. Ascaris lumbricoides
b. Enterobius vermicularis
c. Strongyloides stercoralis
d. Trichuris trichiura
7. A 7-year-old boy's CBC revealed a microcytic anemia with eosinophilia during an office visit for symptoms of diarrhea. The most likely parasite involved in the infection is:
a. Enterobius vermicularis
b. Necator americanus
c. Trichuris trichiura
d. Wuchereria bancrofti
8. Which of the following infections are not diagnosed by finding eggs or lava in fecal specimens:
a. Ascaris lumbricoides
b. Necator spp.
c. Trichinella spiralis
d. Trichuris trichiura
9. Which of the following parasitic diseases is a zoonosis:
a. Ascaris lumbricoides
b. Dracunculus medinensis
c. Strongyloides stercoralis
d. Trichinella spiralis
10. Cutaneous larval migrans is caused by:
a. Ascaris lumbricoides
b. Necator americanus
c. Strongyloides stercoralis
d. Toxocara canis
11. The nematode parasite that may complete its life cycle without leaving the host is:
a. Ascaris lumbricoides
b. Necator americanus
c. Strongyloides stercoralis
d. Toxocara canis
12. All of the following have life cycles that require larval lung migrations EXCEPT:
a. Ascaris lumbricoides
b. Necator americanus
c. Strongyloides stercoralis
d. Trichuris trichiura
13. The diagnostic form recovered in feces in Strongyloides stercoralis infections is the:
a. Adult worm
b. Egg
c. Filariform larva
d. Rhabditiform larva
14. A soldier returning from Iraq noticed a blister above his ankle that subsequently opened while he was swimming in his family pool. On further examination, he noticed a worm in the open blister. The possible parasite in this lesion is:
a. Ancylostoma duodenali
b. Dracunculus medinensis
c. Toxocara canis
d. Visceral larval migrans
15. All of the following infections are diagnosed by finding microfilaria in blood EXCEPT:
a. Wuchereria bancrofti
b. Onchocerca volvulus
c. Loa loa
d. Brugia malayi
16. A microfilaria recovered in a blood sample from a patient from Vietnam had two nuclei at the tip of the tail. The worm was enclosed in a sheath. This parasite is:
a. Brugia malayi
b. Loa loa
c. Onchocera volvulus
d. Wuchereria bancrofti
17. An immigrant from central Africa is exhibiting transient subcutaneous swelling in the arm. A blood smear revealed a sheathed microfilaria with a single row of nuclei present in the posterior of the parasite. The most likely identification is:
a. Brugia malayi
b. Loa loa
c. Onchocerca volvulus
d. Wuchereria bancrofti
18. The diagnosis of Enterobius vermicularis infection is accomplished by observing:
a. Eggs in feces
b. Eggs recovered from the perianal region
c. Larva in feces
d. Trophozoites in feces
19. The rhabditiform larva of Strongyloides stercoralis has a:
a. Long buccal cavity
b. Sheath
c. Large genital primordium
d. Notched tail
20. Closed fecal sanitation systems had directly led to the reduction of all of the following nematode infections EXCEPT:
a. Ascariasis
b. Hookworm disease
c. Strongyloidiasis
d. Trichinosis
21. The diagnostic form of this parasite appears as an oval thin-shelled egg with a clear area around the eight-celled immature embryo. This parasite is:
a. Ascaris lumbricoides
b. Enterobius vermicularis
c. Hookworm
d. Trichuris trichiura
22. The nematode infection that is acquired by ingesting a Cyclops (water flea) is:
a. Dracunculus medinensis
b. Enterobius vermicularis
c. Necator americanus
d. Trichinella spiralis
23. Which of the following organisms or infections could be transmitted in the laboratory:
a. Ascaris lumbricoides—Ascariasis
b. Enterobius vermicularis—pinworm infection
c. Strongyloides stercoralis—Strongyloidiasis
d. Trichuris trichiura—whipworm infection
24. Which of the following parasitic diseases can cause blindness:
a. Brugia malayi
b. Loa loa
c. Onchocerca volvulus
d. Wuchereria bancrofti
25. Elephantiasis is a clinical symptom associated with:
a. Brugia malayi
b. Loa loa
c. Onchocerca volvulus
d. Strongyloides stercoralis
26. Name the parasite shown in the following image:
a. Ascaris lumbricoides egg
b. Enterobius vermicularis egg
c. Hookworm egg
d. Trichuris trichiura egg
27. Name the parasite shown in the following image:
a. Ascaris lumbricoides egg
b. Enterobius vermicularis egg
c. Hookworm egg
d. Trichuris trichiura egg
28. Name the parasite shown in the following image:
a. Ascaris lumbricoides egg
b. Enterobius vermicularis egg
c. Hookworm egg
d. Trichuris trichiura egg
29. Name the parasite shown in the following image:
a. Ascaris lumbricoides egg
b. Enterobius vermicularis egg
c. Hookworm egg
d. Trichuris trichiura egg
30. Name the parasite shown in the following image:
a. Wuchereria bancrofti—microfilaria
b. Filariform larva
c. Pinworm—female
d. Rhabditiform larva
Answer Key for Chapter 2. Nematoda
1. In a general nematode parasite's life cycle, the host may ingest a fertile egg. This stage of the life cycle is referred to as the:
a. Definitive host phase
b. Diagnostic stage
c. Infective stage
d. Method of infection
ANS: D
RATIONALE: See Diagram 2-1
KEY: Nematoda: life cycle | Cognitive level: correlation
2. The nematode infection that may become more severe through ingestion of infective eggs, especially in infected infants, is:
a. Ancylostoma duodenale
b. Enterobius vermicularis
c. Strongyloides stercoralis
d. Trichinella spiralis
ANS: B
RATIONALE: Enterobius vermicularis infections become more severe due to thepruritus caused by new eggs released by dying females, which leads to autoreinfection through ingestion of these new eggs.
KEY: Nematoda: life cycle | Cognitive level: correlation
3. In the Ascaris lumbricoides life cycle, after eggs are ingested, the next stage in the life cycle that must occur before a mature adult can live in the host's intestine is called the:
a. Diagnostic stage
b. Infective stage
c. Liver-lung migration
d. Method of infection
ANS: C
RATIONALE: The liver-lung migration phase of the Ascarus lumbricoides life cycle occurs as the larva form migrates from the intestine to the lungs before returning to the intestine to become a mature adult worm. See Diagram 2-4.
KEY: Nematoda: life cycle | Cognitive level: recall
4. Patients who have heavy infections with Necator americanus may exhibit all of the following symptoms EXCEPT:
a. Diarrhea
b. Larval dermatitis
c. Macrocytic anemia
d. Microcytic anemia
ANS: D
RATIONALE: Microcytic anemia may result from reduced plasma iron levels due to red blood cell loss; heavy worm burdens may result in 100 ml of blood loss per day.
KEY: Nematoda: disease condition | Cognitive level: correlation
5. The nematode egg that appears as a barrel-shaped structure with clear polar plugs at each end of the egg belongs to:
a. Ascaris lumbricoides
b. Enterobius vermicularis
c. Strongyloides stercoralis
d. Trichuris trichiura
ANS: D
RATIONALE: Trichuris trichiura eggs appear as a barrel-shaped structure with clear polar plugs at each end. See drawing and photograph.
KEY: Nematoda: diagnostic form | Cognitive level: recall
6. A slender round worm measuring 25 cm was recovered from a toilet following a child's trip to the bathroom. The specimen most likely is:
a. Ascaris lumbricoides
b. Enterobius vermicularis
c. Strongyloides stercoralis
d. Trichuris trichiura
ANS: A
RATIONALE: Ascaris lumbricoides measure 22-35 cm in length and are often recovered in feces. The adult worm is active and may migrate up the esophagus as well.See life cycle.
KEY: Nematoda: diagnostic form | Cognitive level: correlation
7. A 7-year-old boy's CBC revealed a microcytic anemia with eosinophilia during an office visit for symptoms of diarrhea. The most likely parasite involved in the infection is:
a. Enterobius vermicularis
b. Necator americanus
c. Trichuris trichiura
d. Wuchereria bancrofti
ANS: A
RATIONALE: Necator spp. often causes iron-deficient anemia. Diarrhea and eosinophilia are common symptoms.
KEY: Nematoda: disease symptoms | Cognitive level: correlation
8. Which of the following infections are not diagnosed by finding eggs or lava in fecal specimens:
a. Ascaris lumbricoides
b. Necator spp.
c. Trichinella spiralis
d. Trichuris trichiura
ANS: C
RATIONALE: Trichinella spiralis larvae are ingested in undercooked meat. Freed larvae invade muscle tissue and encyst. Diagnosis is based on finding encysted larvae in biopsied muscle.
KEY: Nematoda: diagnosis | Cognitive level: recall
9. Which of the following parasitic diseases is a zoonosis:
a. Ascaris lumbricoides
b. Dracunculus medinensis
c. Strongyloides stercoralis
d. Trichinella spiralis
ANS: D
RATIONALE: Trichinella spiralis infection is a zoonosis. See life cycle; the normal host(s) include carnivorous mammals.
KEY: Nematoda: life cycle | Cognitive level: recall
10. Cutaneous larval migrans is caused by:
a. Ascaris lumbricoides
b. Necator americanus
c. Strongyloides stercoralis
d. Toxocara canis
ANS: B
RATIONALE: Free living filariform larvae of Necator spp. may invade broken skin. See life cycle.
KEY: Nematoda: life cycle | Cognitive level: correlation
11. The nematode parasite that may complete its life cycle without leaving the host is:
a. Ascaris lumbricoides
b. Necator americanus
c. Strongyloides stercoralis
d. Toxocara canis
ANS: C
RATIONALE: Strongyloides stercoralis is parthenogenic; therefore, fertile eggs hatch inside the host and may become infective without leaving the host.
KEY: Nematoda: life cycle | Cognitive level: recall
12. All of the following have life cycles that require larval lung migrations EXCEPT:
a. Ascaris lumbricoides
b. Necator americanus
c. Strongyloides stercoralis
d. Trichuris trichiura
ANS: D
RATIONALE: Trichuris trichiura eggs are swallowed and hatch to become mature adults in the intestine. All of the parasites mentioned in choices A-C have migrations through the lungs in order to complete the life cycle. See individual life cycle diagrams.
KEY: Nematoda: life cycle | Cognitive level: recall
13. The diagnostic form recovered in feces in Strongyloides stercoralis infections is the:
a. Adult worm
b. Egg
c. Filariform larva
d. Rhabditiform larva
ANS: D
RATIONALE: Eggs released by the adult worm hatch in the intestinal mucosa releasing immature rhabditiform larvae.
KEY: Nematoda: life cycle | Cognitive level: recall
14. A soldier returning from Iraq noticed a blister above his ankle that subsequently opened while he was swimming in his family pool. On further examination, he noticed a worm in the open blister. The possible parasite in this lesion is:
a. Ancylostoma duodenali
b. Dracunculus medinensis
c. Toxocara canis
d. Visceral larval migrans
ANS: B
RATIONALE: The soldier was returning from an endemic area for D. medinensis. This parasite produces a blister that ruptures in water so larvae may be released.
KEY: Nematoda: life cycle | Cognitive level: correlation
15. All of the following infections are diagnosed by finding microfilaria in blood EXCEPT:
a. Wuchereria bancrofti
b. Onchocerca volvulus
c. Loa loa
d. Brugia malayi
ANS: B
RATIONALE: Microfilaria of Onchocerca volvulus are found in the dermis with adults residing in subcutaneous nodules.
KEY: Nematoda: life cycle, Filariae | Cognitive level: recall
16. A microfilaria recovered in a blood sample from a patient from Vietnam had two nuclei at the tip of the tail. The worm was enclosed in a sheath. This parasite is:
a. Brugia malayi
b. Loa loa
c. Onchocera volvulus
d. Wuchereria bancrofti
ANS: A
RATIONALE: Microfilariae are identified by examining their morphologic features. The presence or absence of structures such as sheaths and nuclei in the posterior end of the parasite are characteristics used to identify microfilaria. Brugia malayi may be identified when two nuclei are found at the tip of the parasite's tail that is enclosed in a sheath.
KEY: Nematoda: diagnostic form | Cognitive level: application
17. An immigrant from central Africa is exhibiting transient subcutaneous swelling in the arm. A blood smear revealed a sheathed microfilaria with a single row of nuclei present in the posterior of the parasite. The most likely identification is:
a. Brugia malayi
b. Loa loa
c. Onchocerca volvulus
d. Wuchereria bancrofti
ANS: B
RATIONALE: Microfilariae are identified by examining their morphologic features. The presence or absence of structures such as sheaths and nuclei in the posterior end of the parasite are characteristics used to identify microfilaria. Loa loa is identified when a sheathed organism with a single row of nuclei extending to the tip of the tail of the parasite is observed.
KEY: Nematoda: diagnostic form | Cognitive level: application
18. The diagnosis of Enterobius vermicularis infection is accomplished by observing:
a. Eggs in feces
b. Eggs recovered from the perianal region
c. Larva in feces
d. Trophozoites in feces
ANS: B
RATIONALE: The female worm leaves the anus and dies releasing eggs into the perianal region.
KEY: Nematoda: identification | Cognitive level: recall
19. The rhabditiform larva of Strongyloides stercoralis has a:
a. Long buccal cavity
b. Sheath
c. Large genital primordium
d. Notched tail
ANS: C
RATIONALE: Strongyloides stercoralis larvae can be identified when a large genital primordium is noted. The parasite's eggs hatch in the intestinal mucosa of the host. Larvae are noted in fecal specimens.
KEY: Nematoda: identification | Cognitive level: correlation
20. Closed fecal sanitation systems had directly led to the reduction of all of the following nematode infections EXCEPT:
a. Ascariasis
b. Hookworm disease
c. Strongyloidiasis
d. Trichinosis
ANS: D
RATIONALE: Trichinosis is acquired by eating infected pork. The other parasitic infections have fecal-oral components in the life cycle.Sanitary systems reduce human exposure to contaminated feces.
KEY: Nematoda: identification | Cognitive level: correlation
21. The diagnostic form of this parasite appears as an oval thin-shelled egg with a clear area around the eight-celled immature embryo. This parasite is:
a. Ascaris lumbricoides
b. Enterobius vermicularis
c. Hookworm
d. Trichuris trichiura
ANS: C
RATIONALE: The described egg is seen in feces in hookworm infections.
KEY: Nematoda: identification | Cognitive level: recall
22. The nematode infection that is acquired by ingesting a Cyclops (water flea) is:
a. Dracunculus medinensis
b. Enterobius vermicularis
c. Necator americanus
d. Trichinella spiralis
ANS: A
RATIONALE: Dracunculus medinensis infection is acquired by drinking water containing an infected water flea.
KEY: Nematoda: life cycle | Cognitive level: recall
23. Which of the following organisms or infections could be transmitted in the laboratory:
a. Ascaris lumbricoides—Ascariasis
b. Enterobius vermicularis—pinworm infection
c. Strongyloides stercoralis—Strongyloidiasis
d. Trichuris trichiura—whipworm infection
ANS: B
RATIONALE: Only pinworm eggs become infective after being released into the local environment (in 4 to 6 hours). All others require exposure to soil before embryonating.
KEY: Nematoda: life cycle | Cognitive level: correlation
24. Which of the following parasitic diseases can cause blindness:
a. Brugia malayi
b. Loa loa
c. Onchocerca volvulus
d. Wuchereria bancrofti
ANS: C
RATIONALE: Although Loa loa is referred to as the eyeworm it does not produce blindness because it does not invade other eye structures (only blood vessels) as do the microfilariae of Onchocerca volvulus.
KEY: Nematoda: disease manifestations | Cognitive level: correlation
25. Elephantiasis is a clinical symptom associated with:
a. Brugia malayi
b. Loa loa
c. Onchocerca volvulus
d. Strongyloides stercoralis
ANS: A
RATIONALE: Brugia malayi and Wuchereria bancrofti microfilaria both cause elephantiasis in long-standing infections by obstructing lymphatic ducts. Loa loa and Onchocerca volvulus lives in subcutaneous locations; microfilaria move through blood vessels causing pathology in the face and eyes. Strongyloides stercoralis lives in the intestine and larval forms migrate through the liver and lungs eventually returning to the GI tract.
KEY: Nematoda: pathology and life cycle | Cognitive level: correlation
26. Name the parasite shown in the following image:
a. Ascaris lumbricoides egg
b. Enterobius vermicularis egg
c. Hookworm egg
d. Trichuris trichiura egg
ANS: A
RATIONALE: This view is of an Ascaris lumbricoides egg. The heavy albuminous outer-shell coating indicates that this is a fertile egg.
KEY: Nematoda: parasite identification | Cognitive level: recall
27. Name the parasite shown in the following image:
a. Ascaris lumbricoides egg
b. Enterobius vermicularis egg
c. Hookworm egg
d. Trichuris trichiura egg
ANS: C
RATIONALE: This view is of a hookworm egg. Hookworm eggs cannot be identified to the species level. The final identification relies on recovering the adult worm.
KEY: Nematoda: parasite identification | Cognitive level: recall
28. Name the parasite shown in the following image:
a. Ascaris lumbricoides egg
b. Enterobius vermicularis egg
c. Hookworm egg
d. Trichuris trichiura egg
ANS: B
RATIONALE: This view is of an Enterobius vermicularis (pinworm) egg. These eggs have the characteristic flattened side.
KEY: Nematoda: parasite identification | Cognitive level: recall
29. Name the parasite shown in the following image:
a. Ascaris lumbricoides egg
b. Enterobius vermicularis egg
c. Hookworm egg
d. Trichuris trichiura egg
ANS: D
RATIONALE: This view is of a Trichuris trichiura (whipworm) egg. This egg has the characteristic tray shape.
KEY: Nematoda: parasite identification | Cognitive level: recall
30. Name the parasite shown in the following image:
a. Wuchereria bancrofti—microfilaria
b. Filariform larva
c. Pinworm—female
d. Rhabditiform larva
ANS: D
RATIONALE: This view is the larval form seen in feces in Strongyloides stercoralis infections. Eggs resembling those of hookworms may occasionally be found as well but the usual diagnostic form is the rhabditiform larva.
KEY: Nematoda: parasite identification | Cognitive level: recall
