Parasitology

Question 1

The incorrect match between organism and the appropriate diagnostic procedure is:
A. Onchocerca volvulus—examination of skin snips
B. Cryptosporidium—modified acid-fast stain
C. Echinococcus granulosus—routine ova and parasite examination
D. Schistosoma haematobium—examination of urine sediment

Answer 1

C. Echinococcus granulosus—routine ova and parasite examination

Note: The appropriate procedure for the diagnosis of E. granulosus (hydatid disease) would involve the microscopic examination of hydatid fluid aspirated from a cyst. Immature scolices and/or hooklets would be found in the centrifuged fluid sediment and could be identified under the microscope.

Question 2

In a patient with diarrhea, occasionally Entamoeba histolytica/E. dispar (four nucleated cysts, no chromatoidal bars) are identified as being present;
however, these cells, which are misdiagnosed as protozoa, are really:
A. Macrophages
B. Polymorphonuclear leukocytes
C. Epithelial cells
D. Eosinophils

Answer 2

B. Polymorphonuclear leukocytes

Note: As polymorphonuclear leukocyte (PMN) nuclei in stool begin to fragment and appear to be four
nuclei, they will resemble E. histolytica/E. dispar cysts. However, E. histolytica/E. dispar cysts are rarely seen in cases of diarrhea. The species name E. histolytica is reserved for the true pathogen, whereas E. dispar is used for the nonpathogenic species. Unfortunately, morphologically they look identical. The only time E. histolytica could be identified morphologically would be from
trophozoites containing ingested red blood cells (RBCs). Nonpathogenic E. dispar C would not contain ingested RBCs. The correct way to report these
organisms is Entamoeba histolytica/E. dispar (no trophozoites containing ingested RBCs) or Entamoeba histolytica (trophozoites seen that
contain ingested RBCs). Physicians may treat based on patient symptoms.

Question 3

Charcot–Leyden crystals in stool may be associated with an immune response and are thought to be
formed from the breakdown products of:
A. Neutrophils
B. Eosinophils
C. Monocytes
D. Lymphocytes

Answer 3

B. Eosinophils

Note: When eosinophils disintegrate, the granules reform into Charcot–Leyden crystals.

Question 4

Parasitic organisms that are most often transmitted sexually include:
A. Entamoeba gingivalis
B. Dientamoeba fragilis
C. Trichomonas vaginalis
D. Diphyllobothrium latum

Answer 4

C. Trichomonas vaginalis

Note: T. vaginalis has been well documented to be a sexually transmitted flagellate.

Question 5

The incorrect match between the organism and one method of acquiring the infection is:
A. Trypanosoma brucei rhodesiense—bite of sand fleas
B. Giardia lamblia—ingestion of water
contaminated with cysts
C. Hookworm—skin penetration of larvae from soil
D. Toxoplasma gondii—ingestion of raw or rare meats

Answer 5

A. Trypanosoma brucei rhodesiense—bite of sand fleas

Note: East and West African trypanosomiasis (T. b. rhodesiense
and T. b. gambiense) are caused when infective forms are introduced into the human body through the bite of the tsetse fly, not sand fleas.

Question 6

Upon examination of stool material for Cystoisospora belli, one would expect to see:
A. Cysts containing sporozoites
B. Precysts containing chromatoidal bars
C. Oocysts that are modified acid-fast variable
D. Sporozoites that are hematoxylin positive

Answer 6

C. Oocysts that are modified acid-fast variable

Note: C. belli oocysts in various stages of maturity would be seen in the concentration sediment or possibly the direct, wet preparation; these oocysts would stain positive with modified acid-fast stains.

Question 7

Which specimen is the least likely to provide recovery of Trichomonas vaginalis?
A. Urine
B. Urethral discharge
C. Vaginal discharge
D. Feces

Answer 7

D. Feces

Note: T. vaginalis is site specific. The organisms are found in the urogenital tract; thus, the intestinal tract is not the normal site for these organisms.

Question 8

Which of the following is the best technique to identify Dientamoeba fragilis in stool?
A. Formalin concentrate
B. Trichrome-stained smear
C. Modified acid-fast–stained smear
D. Giemsa’s stain

Answer 8

B. Trichrome-stained smear

Note: Because there is no known cyst form, the best technique to recover and identify D. fragilis trophozoites would be the trichrome-stained
smear.

Question 9

One of the following protozoan organisms has been implicated in waterborne and foodborne outbreaks within the United States. The suspect
organism is:
A. Pentatrichomonas hominis
B. Dientamoeba fragilis
C. Giardia lamblia
D. Balantidium coli

Answer 9

C. Giardia lamblia

Note: For a number of years, G. lamblia has been implicated in both waterborne and foodborne outbreaks from the ingestion of infective cysts within contaminated water and food.

Question 10

A Gram stain from a gum lesion showed what appeared to be amoebae. A trichrome smear showed amoebae with a single nucleus and partially digested PMNs. The correct identification is:
A. Trichomonas tenax
B. Entamoeba histolytica/E. dispar
C. Entamoeba gingivalis
D. Entamoeba polecki

Answer 10

C. Entamoeba gingivalis

Note: E. gingivalis is known to be an inhabitant of the mouth and is characterized by morphology that resembles Entamoeba histolytica/E. dispar. However, E. gingivalis tends to ingest PMNs, whereas Entamoeba histolytica/E. dispar do not.

Question 11

An Entamoeba histolytica trophozoite has the following characteristics:
A. Central karyosome in the nucleus, ingested RBCs, and clear pseudopodia
B. Ingested RBCs, clear pseudopodia, and uneven chromatin on the nuclear membrane
C. Ingested RBCs, clear pseudopodia, and large glycogen vacuoles in cytoplasm
D. Large, blotlike karyosome, ingested white blood cells (WBCs), and granular pseudopods

Answer 11

A. Central karyosome in the nucleus, ingested RBCs, and clear pseudopodia

Note: The trophozoite of E. histolytica has evenly arranged chromatin on the nuclear membrane; a central, compact karyosome in the nucleus; clear pseudopodia; and ingested RBCs in the cytoplasm.

Question 12

A 12-year-old girl is brought to the emergency department with meningitis and a history of swimming in a warm-water spring. Motile amoebae that measure 10 μ in size are seen in the CSF and are most likely:
A. Iodamoeba bütschlii trophozoites
B. Endolimax nana trophozoites
C. Dientamoeba fragilis trophozoites
D. Naegleria fowleri trophozoites

Answer 12

D. Naegleria fowleri trophozoites

Note: N. fowleri are free-living soil and water amoebae that cause primary amoebic meningoencephalitis, or PAM. The number of cases reported is few; however, the infection is very acute and almost always fatal.

Question 13

Characteristics of the rhabditiform (noninfective) larvae of Strongyloides stercoralis include a:
A. Short buccal capsule and large genital primordium
B. Long buccal capsule and pointed tail
C. Short buccal capsule and small genital primordium
D. Small genital primordium and notch in tail

Answer 13

A. Short buccal capsule and large genital primordium

Note: The rhabditiform larvae of S. stercoralis are characterized by the short buccal capsule (mouth) and large genital primordium, whereas hookworm larvae have a long buccal capsule and very small genital primordium.

Question 14

Visceral larva migrans is associated with which of the following organisms?
A. Toxocara—serology
B. Onchocerca—skin snips
C. Dracunculus—skin biopsy
D. Angiostrongylus—CSF examination

Answer 14

A. Toxocara—serology

Note: Toxocara spp. are the cause of visceral larva migrans and occur when humans accidentally ingest the infective eggs of the dog or cat ascarid. The larvae migrate through the deep tissues, including the eye.
The test of choice is the serology.

Question 15

The following organisms are linked with specific, relevant information. The incorrect combination is:
A. Strongyloides stercoralis—internal autoinfection
B. Echinococcus granulosus—hydatid examination
C. Toxoplasma—serology
D. Balantidium coli—common within the United States

Answer 15

D. Balantidium coli—common within the United States

Note: B. coli is a ciliate that can cause watery diarrhea in humans and is associated with pigs; however, it is not
commonly found within the United States. It is the largest of the intestinal protozoa and can be found in
proficiency testing specimens. Therefore, although it is not common, laboratories must still be able to
identify these organisms.

Question 16

Examination of 24-hour unpreserved urine specimen is sometimes helpful in the recovery of:
A. Trichomonas vaginalis trophozoites
B. Schistosoma haematobium eggs
C. Enterobius vermicularis eggs
D. Strongyloides stercoralis larvae

Answer 16

B. Schistosoma haematobium eggs

Note: S. haematobium blood flukes reside in the veins over the bladder. When the eggs are passed from the
body, they are often found in urine; egg viability can also be determined in unpreserved urine.

Question 17

The examination of sputum may be necessary to diagnose infection with:
A. Paragonimus westermani
B. Trichinella spiralis
C. Wuchereria bancrofti
D. Fasciola hepatica

Answer 17

A. Paragonimus westermani

Note: P. westermani adult worms are found in the lung, and eggs may be coughed up in the sputum. Consequently, both sputum and stool (if the sputum containing the eggs is swallowed) are the recommended specimens for examination for the eggs.

Question 18

Two helminth eggs that may resemble one another are:
A. Diphyllobothrium latum and Paragonimus westermani
B. Opisthorchis sinensis and Fasciolopsis buski
C. Taenia saginata and Hymenolepis nana
D. Ascaris lumbricoides and Trichostrongylus

Answer 18

A. Diphyllobothrium latum and Paragonimus westermani

Note: Both D. latum and P. westermani eggs are operculated and approximately the same size. The
morphology is similar, although D. latum has a knob at the abopercular end and P. westermani has a thickened abopercular end and shoulders into which the operculum fits.

Question 19

Eating poorly cooked pork can lead to an infection with:
A. Taenia solium and Trichinella spiralis
B. Taenia saginata and Hymenolepis nana
C. Trichuris trichiura and Hymenolepis diminuta
D. Diphyllobothrium latum and Ascaris lumbricoides

Answer 19

A. Taenia solium and Trichinella spiralis

Note: Both T. solium (pork tapeworm) and T. spiralis can be acquired from the ingestion of raw or poorly cooked pork.

Question 20

An operculated cestode egg that can be recovered from human feces is:
A. Clonorchis sinensis
B. Diphyllobothrium latum
C. Paragonimus westermani
D. Dipylidium caninum

Answer 20

B. Diphyllobothrium latum

Note: D. latum is the only operculated cestode egg that is found in humans; the infection is acquired from the
ingestion of raw freshwater fish.

Question 21

The adult tapeworm of Echinococcus granulosus is found in the intestine of:
A. Dogs
B. Sheep
C. Humans
D. Cattle

Answer 21

A. Dogs

Note: Although the hydatid cysts are found in sheep or in humans (accidental intermediate host), the adult tapeworms of E. granulosus are found in the intestine of the dog.

Question 22

In infections with Taenia solium, humans can serve as the:
A. Definitive host
B. Intermediate host
C. Either the definitive or the intermediate host
D. None of these options

Answer 22

C. Either the definitive or the intermediate host

Note: If humans ingest T. solium cysticerci in uncooked or rare pork, the adult tapeworm will mature within the intestine (human will serve as definitive host); if eggs from the adult tapeworm are ingested, then the
cysticerci will develop in human tissues (accidental intermediate host), causing cysticercosis.

Question 23

Humans acquire infections with Diphyllobothrium latum adult worms by:
A. Ingestion of freshwater crabs
B. Skin penetration of cercariae
C. Ingestion of water chestnuts
D. Ingestion of raw freshwater fish

Answer 23

D. Ingestion of raw freshwater fish

Note: The ingestion of raw freshwater fish containing the encysted larvae of D. latum will result in the development of an adult tapeworm within the human intestine.

Question 24

Humans can serve as both the intermediate and definitive host in infections caused by:
A. Enterobius vermicularis
B. Hymenolepis nana
C. Schistosoma japonicum
D. Ascaris lumbricoides

Answer 24

B. Hymenolepis nana

Note: In infections with H. nana, humans serve as both intermediate and definitive hosts. When ingested,
the oncosphere penetrates the intestinal mucosa, develops into the mature cysticercoid (human is
intermediate host), and returns to the gut, where the adult tapeworm matures (human is definitive host).

Question 25

Babesia has been implicated in disease from both splenectomized and nonsplenectomized patients.
Morphologically, the parasites resemble:
A. Plasmodium falciparum rings
B. Leishmania donovani amastigotes
C. Trypanosoma cruzi trypomastigotes
D. Microsporidial spores

Answer 25

A. Plasmodium falciparum rings

Note: Babesia is an intracellular parasite that closely resembles the ring forms (early trophozoites) of
P. falciparum. Often in babesiosis, there are more rings per cell and the ring form is the only stage seen.

Question 26

Organisms (and infections) that under normal conditions cannot be transmitted in the laboratory are:
A. Cryptosporidium—cryptosporidiosis
B. Taenia solium—cysticercosis
C. Ascaris lumbricoides—ascariasis
D. Enterobius vermicularis—pinworm infections

Answer 26

C. Ascaris lumbricoides—ascariasis

Note: A. lumbricoides eggs require a period of development in the soil before they are infective for humans. The other organisms listed can be transmitted within the laboratory or in the hospital setting.

Question 27

Toxoplasma gondii is characterized by:
A. Possible congenital infection and ingestion of oocysts
B. Cosmopolitan distribution and possible difficulties with interpretation of serological results
C. Neither A nor B
D. Both A and B

Answer 27

D. Both A and B

Note: Infection with T. gondii is acquired through the ingestion of rare or raw meats, infective oocysts from cat feces, or as a congenital transmission. The organism has a cosmopolitan distribution and although serological testing is generally the test of choice, the results may be very difficult to interpret in
certain situations (e.g., congenital infection and immunocompromised patients).

Question 28

Oocysts of Cryptosporidium spp. can be detected in stool specimens using:
A. Modified Ziehl–Neelsen acid-fast stain
B. Gram stain
C. Methenamine silver stain
D. Trichrome stain

Answer 28

A. Modified Ziehl–Neelsen acid-fast stain

Note: The oocysts of Cryptosporidium spp. can be found and identified using microscopic examination of fecal
smears stained with modified acid-fast stains. They appear as purple-red-pink round objects, measuring
approximately 4–6 μ. Often, the four sporozoites and residual body can be seen within the oocyst wall.

Question 29

Which microfilariae are usually not found circulating in the peripheral blood?
A. Brugia malayi
B. Wuchereria bancrofti
C. Onchocerca volvulus
D. Loa loa

Answer 29

C. Onchocerca volvulus

Note: The microfilariae of O. volvulus are normally found in the fluid right under the outer layer of skin. Therefore, the skin snip is the proper specimen to examine.

Question 30

Massive hemolysis, blackwater fever, and central nervous system involvement are most common with:
A. Plasmodium vivax
B. Plasmodium falciparum
C. Plasmodium ovale
D. Plasmodium malariae

Answer 30

B. Plasmodium falciparum

Note: The pathogenic sequelae of malarial infections with P. falciparum are the most severe of the five species of human malaria. They can include massive hemolysis, blackwater fever, and multiple organ involvement,
including the central nervous system (cerebral malaria).

Question 31

Organisms that should be considered in a nursery school outbreak of diarrhea include:
A. Endolimax nana, Giardia lamblia, and Entamoeba coli
B. Giardia lamblia, Dientamoeba fragilis, and Cryptosporidium spp.
C. Cryptosporidium spp., Trichomonas vaginalis, and Entamoeba coli
D. Pentatrichomonas hominis, Dientamoeba fragilis, and Endolimax nana

Answer 31

B. Giardia lamblia, Dientamoeba fragilis, and Cryptosporidium spp.

Note: G. lamblia, D. fragilis, and Cryptosporidium have been implicated in nursery school outbreaks. Among the many protozoa and coccidia found in the human,
these three organisms have become the most likely parasites in this type of setting.

Question 32

The incorrect match between disease and symptoms is:
A. Paragonimiasis—hemoptysis
B. Cryptosporidiosis—watery diarrhea
C. Toxoplasmosis in compromised host—central nervous system symptoms
D. Enterobiasis—dysentery

Answer 32

D. Enterobiasis—dysentery

Note: Infections with E. vermicularis (the pinworm) may cause anal itching, sleeplessness, and possibly some
vaginal irritation or discharge; however, dysentery (bloody diarrhea) has not been associated with this
infection.

Question 33

The formalin–ether (ethyl acetate) concentration procedure for feces is used to demonstrate:
A. Motility of helminth larvae
B. Protozoan cysts and helminth eggs
C. Formation of amoebic pseudopods
D. Trophozoites

Answer 33

B. Protozoan cysts and helminth eggs

Note: The ova and parasite examination contains three components: the direct wet film (demonstrates protozoan trophozoite motility), the formalin–ethyl acetate concentration (demonstrates protozoan cysts, coccidian oocysts, and helminth eggs), and the trichrome or iron hematoxylin–stained smear
(confirms protozoan cysts and trophozoites).

Question 34

Cysts of Iodamoeba bütschlii typically have:
A. Chromatoidal bars with rounded ends
B. A heavily vacuolated cytoplasm
C. A large glycogen vacuole
D. Many ingested bacteria and yeast cells

Answer 34

C. A large glycogen vacuole

Note: The cyst of I. bütschlii is characterized by a large glycogen vacuole that is seen on the wet smear
(stains brown with iodine) and on the permanent stained smear (vacuole will appear clear). Occasionally, the vacuole will be so large that the
organism will collapse on itself.

Question 35

The miracidial hatching test helps to demonstrate the viability of eggs of:
A. Taenia species
B. Schistosoma species
C. Hookworm species
D. Opisthorchis species

Answer 35

B. Schistosoma species

Note: The determination of egg viability is important in schistosomiasis; therefore, the miracidial hatching test is helpful in demonstrating the egg viability of
Schistosoma species. Once the eggs are hatched, the living miracidium larvae will be visible in the water.

Question 36

Organisms that should be considered in a waterborne outbreak of diarrheal disease include:
A. Giardia lamblia and Cryptosporidium spp.
B. Endolimax nana and Entamoeba histolytica
C. Blastocystis hominis and Trichomonas vaginalis
D. Toxoplasma gondii and Schistosoma mansoni

Answer 36

A. Giardia lamblia and Cryptosporidium spp.

Note: Both G. lamblia and Cryptosporidium have been implicated in waterborne outbreaks or diarrheal disease. These infections would result from the ingestion of G. lamblia cysts and/or Cryptosporidium
oocysts.

Question 37

Fecal immunoassays have become more commonly used to diagnose infections with:
A. Endolimax nana and Blastocystis hominis
B. Giardia lamblia and Cryptosporidium spp.
C. Ascaris lumbricoides and Trichuris trichiura
D. Strongyloides stercoralis and Trichomonas vaginalis

Answer 37

B. Giardia lamblia and Cryptosporidium spp.

Note: Rapid fecal immunoassays have become more widely used for the diagnosis of infections with G. lamblia
and Cryptosporidium. For these two organisms, the fecal immunoassays are more sensitive than the routine O&P examination.

Question 38

Primary infections with the microsporidia may originate in:
A. The lung
B. The nervous system
C. The gastrointestinal tract
D. Mucocutaneous lesions

Answer 38

C. The gastrointestinal tract

Note: With the possible exception of direct inoculation infection in the eye, the microsporidia are thought to
initially infect the gastrointestinal (GI) tract through ingestion of the infective spores; infections in other body sites are thought to disseminate from
the GI tract.

Question 39

Eye infections with Acanthamoeba spp. have most commonly been traced to:
A. Use of soft contact lenses
B. Use of hard contact lenses
C. Use of contaminated lens care solutions
D. Failure to remove lenses while swimming

Answer 39

C. Use of contaminated lens care solutions

Note: The majority of eye infections with Acanthamoeba spp. have resulted from the use of contaminated eye care solutions, primarily the use of homemade saline.
It is recommended that all solutions be discarded at the expiration date. Continued use may increase the
risk of environmental contamination of the fluids.

Question 40

Select the most sensitive recovery method for Acanthamoeba spp. from lens care solutions or corneal biopsies.
A. The trichrome staining method
B. The use of monoclonal reagents for the detection of antibody
C. The use of non-nutrient agar cultures seeded with Escherichia coli
D. The Giemsa’s stain method

Answer 40

C. The use of non-nutrient agar cultures seeded with Escherichia coli

Note: Currently, the most sensitive method for the recovery of Acanthamoeba spp. from clinical specimens is the non-nutrient agar culture seeded with E. coli. The
amoebae feed on the bacteria; both trophozoites and cysts can be recovered from the agar surface.

Question 41

The microsporidia are protozoans (now classified with the fungi) that have been implicated in human disease primarily in:
A. Immunocompromised patients
B. Pediatric patients under the age of 5 years
C. Adult patients with congenital
immunodeficiencies
D. Patients who have been traveling in the tropics

Answer 41

A. Immunocompromised patients

Note: Although the microsporidia have been known as pathogens in many groups of animals, their
involvement in humans has primarily been in immunocompromised patients, especially those with
AIDS. Microsporidia can be found in different tissues, and currently there are approximately 10 genera implicated in human disease.

Question 42

When staining Cystoisospora belli oocysts with modified acid-fast stains, the important difference between these methods and the acid-fast stains used for acid-fast bacilli (AFB) is:
A. The staining time is much longer with regular AFB acid-fast stains
B. The decolorizer is weaker than acid alcohol used for AFB decolorizing
C. A counterstain must be used for the modified methods
D. The stain is more concentrated when staining for AFB

Answer 42

B. The decolorizer is weaker than acid alcohol used for AFB decolorizing

Note: The decolorizer in modified acid-fast stains (Kinyoun’s cold method, modified hot method) is
usually 1% sulfuric acid rather than the stronger acid alcohol used in the routine AFB stains.

Question 43

The incorrect match between symptoms and disease is:
A. Dysentery—amebiasis
B. Malabsorption syndrome—giardiasis
C. Cardiac involvement—chronic Chagas disease
D. Myalgias—trichuriasis

Answer 43

D. Myalgias—trichuriasis

Note: T. trichiura (whipworm) may cause diarrhea and occasionally dysentery in very heavy infections;
however, the worms are confined to the intestine, and myalgias are not seen in this helminth infection.

Question 44

The incorrect match between organism and characteristic is:
A. Chilomastix mesnili—Shepherd’s crook and lemon shape
B. Plasmodium malariae—“band troph”
C. Hymenolepis nana—striated shell
D. Wuchereria bancrofti—sheathed microfilariae

Answer 44

C. Hymenolepis nana—striated shell

Note: H. nana has a thin eggshell containing a six-hooked
embryo (oncosphere) and polar filaments that lie between the eggshell and the embryo. The
striated eggshell is generally associated with Taenia spp. eggs.

Question 45

The incorrect match between method and method objective is:
A. Direct wet examination—detection of organism motility
B. Knott’s concentration—the recovery of operculated helminth eggs
C. Baermann’s concentration—the recovery of Strongyloides
D. Permanent stained fecal smear—confirmation of protozoa

Answer 45

B. Knott’s concentration—the recovery of operculated helminth eggs

Note: The Knott concentration is designed to allow the recovery of microfilariae from a blood specimen.
Dilute formalin (2%) is used; blood is introduced into the formalin, the red cells lyse, and the sediment can
be examined as a wet preparation or permanent stained smear (Giemsa’s or hematoxylin-based stain) for the presence of microfilariae.

Question 46

The incorrect match between organism and characteristic is:
A. Dientamoeba fragilis—tetrad karyosome in the nucleus
B. Toxoplasma gondii—diagnostic serology
C. Echinococcus granulosus—daughter cysts
D. Schistosoma mansoni—egg with terminal spine

Answer 46

D. Schistosoma mansoni—egg with terminal spine

Note: The egg of S. mansoni is characterized by a large lateral spine; S. haematobium has the characteristic
terminal spine.

Question 47

There are few procedures considered STAT in parasitology. The most obvious situation would be:
A. Ova and parasite examination for giardiasis
B. Baermann’s concentration for strongyloidiasis
C. Blood films for malaria
D. Culture of amoebic keratitis

Answer 47

C. Blood films for malaria

Note: The request for blood films for malaria should always be considered a stat request. Any laboratory
providing these services should be available 24 hours a day, 7 days a week. In cases of P. falciparum malaria, any delay in diagnosing the infection could be fatal for the patient.

Question 48

An immunosuppressed man has several episodes of pneumonia, intestinal pain, sepsis with gram-negative rods, and a history of military
service in Southeast Asia 20 years earlier. The most likely cause is infection with:
A. Trypanosoma cruzi
B. Strongyloides stercoralis
C. Naegleria fowleri
D. Paragonimus westermani

Answer 48

B. Strongyloides stercoralis

Note: A latent infection with S. stercoralis acquired years before may cause severe symptoms in the immunosuppressed patient (“autoinfective” capability of life cycle and migratory route of the larvae through the body).

Question 49

In a pediatric patient, the recommended clinical specimen for recovery of Enterobius vermicularis
is the:
A. Stool specimen
B. Sigmoidoscopy scrapings
C. Duodenal aspirates
D. Series of Scotch tape preparations

Answer 49

D. Series of Scotch tape preparations

Note: In a pediatric patient, the most appropriate diagnostic test for recovery of Enterobius vermicularis eggs is a series of Scotch tape preparations.

Question 50

Which parasite causes eosinophilic
meningoencephalitis, a form of larva
migrans causing fever, headache, stiff neck, and increased cells in the spinal fluid?
A. Necator americanus
B. Angiostrongylus cantonensis
C. Ancylostoma braziliense
D. Strongyloides stercoralis

Answer 50

B. Angiostrongylus cantonensis

Note: Eosinophilic meningoencephalitis is a form of larva
migrans and is caused by A. cantonensis, the rat lungworm. This Pacific area infection is associated
with CSF symptoms and sometimes eye involvement.

Question 51

“Cultures of parasites are different from bacterial cultures; no quality control is needed.” This statement is:
A. True, if two tubes of media are set up for each patient
B. True, if the media are checked every 24 hours
C. False, unless two different types of media are used
D. False, and organism and media controls need to be set up

Answer 51

D. False, and organism and media controls need to be set up

Note: Duplicate cultures should be set up, and specific American Type Culture Collection (ATCC) strains
should be cultured along with the patient specimens to confirm that the culture system is operating properly. This approach is somewhat different from that used in diagnostic bacteriology and mycology.

Question 52

Protozoan cysts were seen in a concentration sediment and tentatively identified as Entamoeba
coli. However, the organisms were barely visible on the permanent stained smear because:
A. The organisms were actually not present in the concentrate sediment
B. There were too few cysts to allow identification on the stained smear
C. E. coli cysts were present but poorly fixed
D. The concentrate and permanent stained smear were not from the same patient

Answer 52

C. E. coli cysts were present but poorly fixed

Note: As E. coli cysts mature, the cyst wall becomes more impenetrable to fixatives. Consequently, the cysts
may be visible in the concentrate sediment but appear very distorted or pale on the permanent stained smear.

Question 53

When humans have hydatid disease, the causative agent and host classification are:
A. Echinococcus granulosus—accidental intermediate host
B. Echinococcus granulosus—definitive host
C. Taenia solium—accidental intermediate host
D. Taenia solium—definitive host

Answer 53

A. Echinococcus granulosus—accidental intermediate host

Note: The cause of hydatid disease is E. granulosus, and the human is classified as the accidental intermediate host. Infection occurs when humans accidentally ingest the eggs of E. granulosus and the hydatid cysts develop in the liver, lung, and other organs of the human instead of sheep (normal cycle).

Question 54

A 45-year-old hunter developed fever, myalgia, and periorbital edema. He has a history of bear meat consumption. The most likely causative agent is:
A. Toxoplasma gondii
B. Taenia solium
C. Hymenolepis nana
D. Trichinella spiralis

Answer 54

D. Trichinella spiralis

Note: Bear meat is another excellent source of T. spiralis. In this case, the patient had evidently consumed poorly cooked bear meat, thus ingesting the encysted larvae of T. spiralis.

Question 55

In a condition resulting from the accidental ingestion of eggs, the human becomes the intermediate rather than the definitive host. The correct answer is:
A. Trichinosis
B. Cysticercosis
C. Ascariasis
D. Strongyloidiasis

Answer 55

B. Cysticercosis

Note: The accidental ingestion of T. solium eggs can result in the disease called cysticercosis. The cysticerci will
develop in a number of different tissues, including the brain, and the human is the accidental intermediate host.

Question 56

A transplant patient on immunosuppressive drugs developed increasing diarrhea. The most
likely combination of disease and diagnostic procedure is:
A. Trichinosis and trichrome stain
B. Microsporidiosis and modified trichrome stain
C. Toxoplasmosis and Gram stain
D. Paragonimiasis and wet preparation

Answer 56

B. Microsporidiosis and modified trichrome stain

Note: The fact that the patient has received a transplant, is on immunosuppressive drugs, and has continuing diarrhea suggests microsporidiosis; the appropriate
diagnostic test would be modified trichrome staining of fecal material.

Question 57

After returning from a 2-year stay in India, a patient has eosinophilia, an enlarged left spermatic cord, and bilateral inguinal lymphadenopathy.
The most likely clinical specimen and organism match is:
A. Thin blood films—Leishmania
B. Urine—concentration for Trichomonas vaginalis
C. Thin blood films—Babesia
D. Thick blood films—microfilariae

Answer 57

D. Thick blood films—microfilariae

Note: Based on the history, the most relevant procedure to perform is the preparation and examination of thick
blood films for the recovery and identification of microfilariae. The symptoms suggest early filariasis.

Question 58

Patients with severe diarrhea should use “enteric precautions” to prevent nosocomial infections with:
A. Giardia lamblia
B. Ascaris lumbricoides
C. Cryptosporidium spp.
D. Cystoisospora belli

Answer 58

C. Cryptosporidium spp.

Note: Cryptosporidium oocysts (unlike those of C. belli) are immediately infective when passed in stool, and
nosocomial infections have been well documented with this coccidian.

Question 59

A 60-year-old Brazilian patient with cardiac irregularities and congestive heart failure suddenly dies. Examination of the myocardium revealed numerous amastigotes, an indication that the cause of death was most likely:
A. Leishmaniasis with Leishmania donovani
B. Leishmaniasis with Leishmania braziliense
C. Trypanosomiasis with Trypanosoma gambiense
D. Trypanosomiasis with Trypanosoma cruzi

Answer 59

D. Trypanosomiasis with Trypanosoma cruzi

Note: T. cruzi, the cause of Chagas disease, has two forms within the human: the trypomastigote in the blood and the amastigote in the striated muscle (usually cardiac muscle and intestinal tract muscle).

Question 60

When malaria smears are requested, what patient information should be obtained?
A. Diet, age, sex
B. Age, antimalarial medication, sex
C. Travel history, antimalarial medication, date of return to United States
D. Fever patterns, travel history, diet

Answer 60

C. Travel history, antimalarial medication, date of return to United States

Note: Travel history (areas of drug resistance), the date of return to the United States (primary versus relapse
case), and history of antimalarial medication and illness (severe illness, few organisms on smear) are very important questions to ask. Without this information, a malaria diagnosis can be missed or delayed with severe patient consequences.

Question 61

In an outbreak of diarrheal disease traced to a municipal water supply, the most likely causative agent is:
A. Cryptosporidium spp.
B. Cystoisospora belli
C. Entamoeba histolytica
D. Dientamoeba fragilis

Answer 61

A. Cryptosporidium spp.

Note: Cryptosporidium oocysts have been transmitted through contaminated municipal water supplies. Such outbreaks have been well documented.

Question 62

Within the United States, sporadic mini-outbreaks of diarrheal disease have been associated with the ingestion of strawberries, raspberries, fresh basil, mesclun (baby lettuce leaves), and snow peas. The most likely causative agent is:
A. Dientamoeba fragilis
B. Cyclospora cayetanensis
C. Schistosoma mansoni
D. Cystoisospora belli

Answer 62

B. Cyclospora cayetanensis

Note: The coccidian C. cayetanensis has been linked to mini-outbreaks of diarrheal disease. Epidemiological
evidence strongly implicates various berries, basil, mesclun, and snow peas as likely causes. These outbreaks are very sporadic and tend to occur
primarily in March through May.

Question 63

Which of the following statements is true regarding onchocerciasis?
A. The adult worm is present in the blood
B. The microfilariae are in the blood during the late evening hours
C. The diagnostic test of choice is the skin snip
D. The parasite resides in the deep lymphatics

Answer 63

C. The diagnostic test of choice is the skin snip

Note: The adult O. volvulus reside in subcutaneous nodules, and the microfilariae are found in the fluids right under the outer layers of skin; thus, the appropriate diagnostic test is the microscopic examination of skin
snips for the presence of microfilariae.

Question 64

The most prevalent helminth to infect humans is:
A. Enterobius vermicularis, the pinworm
B. Ascaris lumbricoides, the large intestinal roundworm
C. Taenia saginata, the beef tapeworm
D. Schistosoma mansoni, one of the blood flukes

Answer 64

A. Enterobius vermicularis, the pinworm

Note: The pinworm, E. vermicularis, is the most common parasitic helminth infection throughout the world, and the eggs are infective within just a few hours. Some have said, “You either had the infection as a child, have it now, or will have it again when you
have children.”

Question 65

A helminth egg is described as having terminal polar plugs. The most likely helminth is:
A. Hookworm
B. Trichuris trichiura
C. Fasciola hepatica
D. Diphyllobothrium latum

Answer 65

B. Trichuris trichiura

Note: The eggs of T. trichiura (the whipworm) have been described as being barrel shaped with a thick shell
and two polar plugs.

Question 66

Ingestion of which of the following eggs will result in infection?
A. Strongyloides stercoralis
B. Schistosoma japonicum
C. Toxocara canis
D. Opisthorchis sinensis

Answer 66

C. Toxocara canis

Note: The eggs of T. canis are infectious for humans and cause visceral larva migrans. These ascarid eggs of the dog can infect humans; the eggs hatch and the larvae wander through the deep tissues, occasionally the eye. In this case, the human becomes the accidental intermediate host.

Question 67

Plasmodium vivax and Plasmodium ovale are similar because they:
A. Exhibit Schüffner’s dots and have a true relapse in the life cycle
B. Have no malarial pigment and multiple rings
C. Commonly have appliqué forms in the red cells
D. Have true stippling, do not have a relapse stage, and infect old red cells

Answer 67

A. Exhibit Schüffner’s dots and have a true relapse in the life cycle

Note: Both P. vivax and P. ovale infect young red cells, have true stippling (Schüffner’s dots), contain malarial
pigment, and have a true relapse stage in the life cycle.

Question 68

The term internal autoinfection can be associated with the following parasites:
A. Cryptosporidium spp. and Giardia lamblia
B. Cystoisospora belli and Strongyloides stercoralis
C. Cryptosporidium spp. and Strongyloides stercoralis
D. Giardia lamblia and Cystoisospora belli

Answer 68

C. Cryptosporidium spp. and Strongyloides stercoralis

Note: Both Cryptosporidium and S. stercoralis have an internal autoinfection capability in their life cycles.This means that the cycle and infection can continue even after the patient has left the endemic area. In
the case of Cryptosporidium, the cycle continues in patients who are immunocompromised and unable
to self-cure.

Question 69

Microsporidia have been identified as causing severe diarrhea, disseminated disease in other body sites, and ocular infections. Routes of infection have been identified as:
A. Ingestion
B. Inhalation
C. Direct contamination from the environment
D. Ingestion, inhalation, and direct contamination

Answer 69

D. Ingestion, inhalation, and direct contamination

Note: Infectious routes for microsporidial infections have
been confirmed as ingestion and inhalation of the spores; direct transfer of infectious spores from
environmental surfaces to the eyes has also been reported.

Question 70

An immunocompromised patient continues to have diarrhea after repeated ova and parasites (O&P) examinations (sedimentation
concentration, trichrome permanent stained smear) were reported as negative; organisms that might be responsible for the diarrhea
include:
A. Cryptosporidium spp., Giardia lamblia, and Cystoisospora belli
B. Giardia lamblia, microsporidia, and
Endolimax nana
C. Taenia solium and Endolimax nana
D. Cryptosporidium spp. and microsporidia

Answer 70

D. Cryptosporidium spp. and microsporidia

Note: Routine O&P examinations usually do not allow the detection of Cryptosporidium spp. oocysts and
microsporidial spores; special stains are required. Modified acid-fast stains for coccidia and modified trichrome stains for the microsporidial spores are recommended.

Question 71

Confirmation of an infection with microsporidia can be achieved by seeing:
A. The oocyst wall
B. Sporozoites within the spore
C. Evidence of the polar tubule
D. Organisms stained with modified acid-fast stains

Answer 71

C. Evidence of the polar tubule

Note: Confirmation of an infection with microsporidial spores can be achieved by seeing evidence of the
polar tubule within the spores (horizontal or diagonal line across/within the spore).

Question 72

Early ring stages of the fifth human malaria, Plasmodium knowlesi, resemble those of:
A. Plasmodium malariae
B. Plasmodium ovale
C. Plasmodium falciparum
D. Plasmodium vivax

Answer 72

C. Plasmodium falciparum

Note: The early ring stages of Plasmodium knowlesi resemble those of P. falciparum.

Question 73

Parasite stages that are immediately infective for humans on passage from the gastrointestinal tract include:
A. Schistosoma spp. eggs
B. Toxoplasma gondii bradyzoites
C. Giardia lamblia trophozoites
D. Cryptosporidium spp. oocysts

Answer 73

D. Cryptosporidium spp. oocysts

Note: Cryptosporidium spp. oocysts are immediately infectious when passed in the stool, regardless
of the stool consistency (formed—liquid).

Question 74

Older developing stages (trophs, schizonts) of the fifth human malaria, Plasmodium knowlesi, resemble those of:
A. Plasmodium malariae
B. Plasmodium ovale
C. Plasmodium falciparum
D. Plasmodium vivax

Answer 74

A. Plasmodium malariae

Note: The older developmental stages of Plasmodium knowlesi (trophs, schizonts) resemble those seen in
infections with P. malariae (band forms, rosette schizonts).

Question 75

Autofluorescence requires no stain and is recommended for the identification of:
A. Entamoeba histolytica cysts
B. Toxoplasma gondii tachyzoites
C. Dientamoeba fragilis trophozoites
D. Cyclospora cayetanensis oocysts

Answer 75

D. Cyclospora cayetanensis oocysts

Note: Autofluorescence requires no stain and is often recommended for confirmation of Cyclospora
cayetanensis oocysts.

Question 76

Key characteristics of infection with Plasmodium knowlesi include:
A. Rapid erythrocytic cycle (24 hr), will infect all ages of RBCs, and can cause serious disease
B. Erythrocytic cycle limited to young RBCs and causes a relatively benign disease
C. The possibility of a true relapse from the liver, infection in older RBCs, and causes serious disease
D. Extended life cycle (72 hr), will infect all ages of RBCs, and disease is similar to that caused by P. ovale

Answer 76

A. Rapid erythrocytic cycle (24 hr), will infect all ages of RBCs, and can cause serious disease

Note: Key characteristics of an infection with Plasmodium knowlesi include a rapid life cycle (24 hr), the potential to infect all ages of RBCs, and the possibility of serious symptoms similar to those seen with P. falciparum infections. There is no relapse from the liver with this species.

Question 77

Microsporidial infections can be confirmed using:
A. Light microscopy and modified trichrome stains
B. Phase contrast microscopy and routine trichrome stains
C. Electron microscopy and modified acid-fast stains
D. Fluorescence microscopy and hematoxylin stains

Answer 77

A. Light microscopy and modified trichrome stains

Note: An infection with microsporidia can be confirmed using modified trichrome stains (10X the normal dye
content found in routine trichrome stains) and light microscopy. The internal polar tubule will be visible
within some of the spores; this will serve as confirmation of the infection.

Question 78

Although the pathogenicity of Blastocystis hominis remains controversial, newer information
suggests that:
A. Most organisms are misdiagnosed as artifacts
B. Numerous strains/species are included in the name, some of which are pathogenic and some are nonpathogenic
C. The immune status of the host is solely responsible for symptomatic infections
D. The number of organisms present determines pathogenicity

Answer 78

B. Numerous strains/species are included in the name, some of which are pathogenic and some are nonpathogenic

Note: The name Blastocystis hominis contains approximately 10 different strains/species that are morphologically identical; some are pathogenic and some are nonpathogenic. Because we cannot separate these organisms by morphology, this probably explains
why some patients are symptomatic and some remain asymptomatic with this infection.

Question 79

Potential problems using EDTA anticoagulant and holding the blood too long prior to preparation of
thick and thin blood films include:
A. Changes in parasite morphology, loss of organisms within several hours, and poor staining
B. Loss of Schüffner’s dots, poor adherence of the blood to the glass slide, and parasites beginning
the vector cycle within the tube of blood
C. Neither A nor B
D. All of these options

Answer 79

D. All of these options

Note: There are many changes that occur if blood is held longer than 1–2 hours prior to thick and thin blood
film preparation. These include changes in parasite morphology, loss of parasites, poor staining, poor
adherence of the blood to the slide, and the parasites beginning that portion of the life cycle that normally
occurs within the vector. These changes are merely one reason that the ordering, specimen collection,
processing, examination, and reporting for thick/thin blood films are considered STAT procedures.

Question 80

Which of the following is a key characteristic of the thick blood film?
A. The ability to see the parasite within the RBCs
B. The ability to identify the parasites to the species level
C. The examination of less blood than the thin blood film
D. The necessity to lake the RBCs during or prior to staining

Answer 80

D. The necessity to lake the RBCs during or prior to staining

Note: With the thick blood film, there is more blood per slide than on the thin film, resulting in greater sensitivity. It is difficult to identify the parasite to the species level from the thick blood film. The RBCs are “laked” while drying or during staining, making it impossible to observe the parasites within the RBCs.