Evaluative Exam (Parasitology)

Question 1

Enterobius vermicularis infection is
usually diagnosed by finding

A. Eggs in perianal specimens
B. Larvae in perianal specimens
C. Larvae in feces
D. Eggs in the feces

Answer 1

A. Because the eggs of E. vermicularis are usually deposited on the perianal area, cellulose
tape slides are recommended for collecting the
eggs.

Question 2

The best direct diagnosis of Echinococcus
granulosus infection in humans is made
by identification of

A. Adult worms in the intestine
B. Adult worms in tissues
C. Eggs in feces
D. Hydatid cysts in tissues

Answer 2

D. When E. granulosus eggs are ingested by an
intermediate herbivorous host, including humans,
they usually develop into hydatid cysts in which
invaginated larval scolices are produced

Question 3

Which statement is correct for specimen
collection and processing?

A. Stool samples can contain urine.
B. Stools can be frozen without affecting
parasitic structure.
C. Liquid stools are best for detecting
ameba and flagellate trophozoites.
D. Unpreserved stools can remain at
room temperature for up to 72 hours.

Answer 3

C. Fresh liquid stools are more likely to contain
motile protozoan trophozoites that can be detected in saline wet mounts

Question 4

Cysts are the infective stage of this
intestinal flagellate.

A. Balantidium coli
B. Dientamoebafragilis
C. Entamoeba coli
D. Giardia lamblia

Answer 4

D. Cysts are the infective stage of most intestinal parasites. D. fragilis is currently classified
as a flagellate, even though it does not produce a
flagellum

Question 5

Eggs or larvae recovered in the stool are
not routinely used to diagnose infections
caused by which one of the following
helminths?

A. Trichinella spiralis
B. Strongyloides stercomlis
C. Necator americanus
D. Ascaris lumbricoides

Answer 5

A. Although T. spiralis adults live in the intestinal
mucosa, they are rarely seen.

Question 6

Many parasites have different stages of
growth within different hosts. The host
where the sexual reproductive stage of the
parasites exists is called the

A. Commensal
B. Definitive host
C. Intermediate host
D. Vector

Answer 6

B. In parasites with a sexual and asexual stage
of development, the definitive host is the host in
which the sexual stage of the parasite occurs

Question 7

Species identification of an immature
amebic cyst can be very difficult. The
presence of a large glycogen mass is
sometimes seen in

A. Dientamoebafragilis
B. Endolimax nana
C. Entamoeba coli
D. Entamoeba histolytica

Answer 7

C. Young cysts of E. coli can have a large
glycogen mass that pushes two nuclei to the
outer edge of the cell.

Question 8

Which of the following is typical in cysts
of lodamoeba biitschlii?

A. A glycogen mass
B. Blunt chromatoidal bars
C. Four nuclei with large karyosomes
D. Many ingested bacteria

Answer 8

A. Mature cysts of I. biitschlii are usually ovoid,
with a single nucleus with a large eccentric
karyosome.

Question 9

Which of the following is the most
important feature in differentiating cysts
of Entamoeba histolytica from E. dispar?

A. Number of nuclei
B. Size of the cyst
C. Shape of the karyosome
D. Distinguishing surface antigens by
immunologic assays

Answer 9

D. E. histolytica and E. dispar cannot be morphologically differentiated

Question 10

Which of the following findings in a
peripheral blood smear is especially
associated with tissue-invading helminths
but may also be found in a variety of
allergic conditions and other diseases?

A. Eosinophilia
B. Leukopenia
C. Lymphocytosis
D. Neutropenia

Answer 10

A. Although the condition may vary from patient
to patient, eosinophilia is often found in association with infections with tissue-invading nematodes.

Question 11

A 48-year-old man from Texas developed
fever and weakness 16 days after a
hunting trip in northwest Tanzania.
Several days after the onset of fever, he
noticed a raised, tender, erythematous
nodule (6-8 cm in diameter) on the
posterior aspect of his right arm. He was
hospitalized in Africa and treated for
5 days with a cephalosporin for presumed
cellulitis. After little improvement, he
returned to Texas. On arrival, the patient
had a temperature of 38.9°C (102°F), a
morbilliform rash of the trunk, and rightsided, anterior cervical lymphadenopathy.
Cerebrospinal fluid contained 12 red cells
and 18 mononuclear cells/uL and a normal
protein level (32 mg/dL). Laboratory tests
of peripheral blood revealed a hemoglobin
level of 107 g/L, a white cell count of
2.4 X 109/L, and a platelet count of
75 X 109/L. The diagnosis was made by
finding the extracellular flagellate parasite
in a peripheral blood smear. Which of the
following is the most probable etiologic
agent of this infection?

A. Leishmania donovani
B. Trypanosoma brucei
C. Tiypanosoma cruzi
D. Toxoplasma gondii

Answer 11

B. The symptoms and history for this patient are
compatible with trypanosomiasis (African sleeping sickness) caused by T. brucei.

Question 12

Which species of malaria parasite usually
has ameboid trophozoites and produces
small reddish dots in the red blood cell
cytoplasm?

A. Plasmodium knowlesi
B. Plasmodium falciparum
C. Plasmodium malariae
D. Plasmodium vivax

Answer 12

D. The trophozoites of P. vivax often develop fine
pseudopodia and large vacuoles and are described
as ameboid; infected red blood cells (RBCs) contain clumps of malarial pigment called Shiiffner’s
dots. P. malariae cytoplasm is much more compact, and infected RBCs lack Shiiffner’s dots.

Question 13

With a fecal specimen, which one of the
following is the most dependable
procedure for the accurate, specific
diagnosis of an intestinal amebic
infection?

A. Direct saline wet mount
B. Direct iodine wet mount
C. Permanently stained smear
D. Formalin-ethyl acetate sedimentation
technique

Answer 13

C. The permanently stained smear is especially
recommended for identification of trophozoites,
for confirmation of species, and for keeping a permanent record of the organisms found.

Question 14

In an examination of stained blood films,
Babesia spp. are likely to resemble

A. Leishmania donovani
B. Plasmodiumfalciparum
C. Toxoplasma gondii
D. Trypanosoma cruzi

Answer 14

B. Babesia spp. are sporozoan parasites of
RBCs that have been recognized as causing
febrile illness in humans. The
parasites often appear as small rings within
infected RBCs, resembling P. falciparum trophozoites. The pathognomic form of Babesia is the
“Maltese cross,” four ring forms inside a single
RBC.

Question 15

Which of the following is a mercurycontaining fixative used to preserve
parasites in stool specimens?

A. Formalin
B. Sodium acetate
C. Buffered glycerol
D. Polyvinyl alcohol

Answer 15

D. Polyvinyl alcohol (PVA) is a commonly used
fixative for stool specimens. This preservative
contains mercury and is used to fix fecal samples
for making permanently stained smears.

Question 16

Examination of a fecal smear following
acid-fast stain reveals round acid-fast
positive structures 8-10 um in diameter.
You should suspect

A. Cryptosporidium
B. Cyclospom
C. Isospora
D. Microsporidia

Answer 16

B. Although all the organisms listed have some
degree of acid-fast positivity, only Cyclospora
forms oocysts in the size range of 8-10 um. The
oocysts of Cryptosporidium are generally 4—6 um
in diameter and are generally strongly acid-fast
positive.

Question 17

A 22-year-old male presents to his family
physician complaining of fatigue, muscle
pain, periorbital edema, and fever. He
denies travel outside the U.S. The
physician suspects infectious mononucleosis; however, serologic tests for infectious mononucleosis are negative. The
complete blood count revealed a slightly
elevated white blood count, and there were
10% eosinophils on the differential.
Which of the following should be
considered part of the differential
diagnosis?

A. Ascaris lumbricoides
B. Taenia solium
C. Trichinella spiralis
D. Trypanosoma cruzi

Answer 17

C. The early symptoms of trichinosis can
resemble infectious mononucleosis. The presence of periorbital edema (swelling around the
eyes) in this patient and hemorrhaging in the nail
beds is suggestive of trichinosis. Eosinophilia
also indicates a parasitic infection.

Question 18

Which Schistosoma species has a large
terminal spine?

A. S. haematobium
B. S.japonicum
C. S. mansoni
D. S. mekongi

Answer 18

A. The ova of Schistosoma contain a spine.
5. haematobium ova have a large prominent
spine on one end. S. mansoni has a prominent
lateral spine, whereas the spine of S. japonicurn
is small and inconspicuous. S. mekongi is a rare
human pathogen.

Question 19

Elephantiasis is a complication associated
with which of the following?

A. Cysticercosis
B. Guinea worm
C. Hydatid cyst disease
D. Filariae

Answer 19

D. Adult filarial helminths typically inhabit the
lymph vessels. They produce inflammation and
swelling of the lymph vessels, often in the legs
and sometimes the scrotum.

Question 20

A patient with history of human immunodeficiency virus infection presents with a
5-day history of diarrhea and weight loss.
A series of stool specimens is collected
and examined for the presence of ova and
parasites. An acid-fast stain on direct
smear reveals pink-stained round
structures approximately 4 (am in
diameter. The most likely pathogen is

A. Blastocystis hominis
B. Cryptosporidium sp.
C. Isospora sp.
D. Microsporidium

Answer 20

B. Although all these organisms are potential
pathogens of immunocompromised patients, only
Cryptosporidium produces acid-fast positive
oocysts about 4-6 um in diameter.

Question 21

A 55-year-old female presents to her
physician complaining of a fever that
“comes and goes” and fatigue. A complete
blood count reveals decreased red blood
cell count and hemoglobin. History
reveals the patient recently traveled
through Europe and Africa. You should
suspect

A. Cutaneous larval migrans
B. Filariasis
C. Malaria
D. Trichinella

Answer 21

C. One of the classic signs of malaria is a fever
that occurs in cycles. As the infection is developing, all the parasites are in approximately the same
stage of development.

Question 22

The disease most commonly associated
with Acanthamoeba sp. is

A. Diarrhea
B. Keratitis
C. Liver abscess
D. Meningoencephalitis

Answer 22

B. Acanthamoeba is a free-living ameba rarely
causing human infections

Question 23

A modified trichrome stain of a fecal
smear can be used to detect microsporidia.
Which of the following would describe the
appearance of this parasite in this stain?

A. Purple circles, 10-15 um in diameter
B. Pink ovals, 1-3 urn in diameter
C. Blue ovals, 4-6 urn in diameter
D. Fluorescent circles, 8-12 um in
diameter

Answer 23

B. The small size and variable staining of the
microsporidia make their detection difficult.
Tissue examination by electron microscopy is
the most specific diagnostic method.

Question 24

Hydatid cysts in humans are due to
ingestion of a tapeworm stage normally
found in canines. This stage is the

A. Cercaria
B. Cercocystis
C. Cysticercus
D. Embryonated egg

Answer 24

D. Echinococcus granulosus is a tapeworm that
lives as an adult in the small intestines of carnivores, primarily dogs, wolves, and other canines.

Question 25

Oocysts, the infective stage of Toxoplasma
gondii, is found in

A. Cat feces
B. Human feces
C. Undercooked pork
D. Undercooked beef

Answer 25

A. T. gondii is a protozoan parasite of humans
and a variety of lower animals. Human infections can be congenital or can result from ingestion of material containing oocysts from cat
feces or from eating undercooked beef, lamb, or
pork containing toxoplasma cysts.

Question 26

A 15-um pear-shaped flagellate with a
visible parabasal body and “falling leaf”
motility in a direct saline mount of a
diarrheal stool specimen is most probably

A. Balantidium coli
B. Chilomastix mesnili
C. Giardia lamblia
D. Trichomonas hominis

Answer 26

C. All the flagellates listed are pear shaped, but
only C. mesnili and G. lamblia are usually as
large as 15 jam. B. coli is a ciliate.

Question 27

This parasitic infection may result in
vitamin B]2 deficiency, and individuals
with pernicious anemia are predisposed
to more severe symptoms.

A. Diphyllobothrium latum
B. Echinococcus granidosus
C. Hymenolepis diminuta
D. Taenia saginata

Answer 27

A. D. latum is a tapeworm that has been linked
to vitamin B]2 deficiencies in individuals of
Scandinavian descent

Question 28

Knowledge of nocturnal periodicity is
especially important in the diagnosis of
certain infections caused by

A. Babesia
B. Plasmodium
C. Microfilariae
D. Trypanosoma

Answer 28

C. Transmission of filariasis depends on the
presence of microfilariae in the bloodstream at the
time the vector bites, and the periodicity of microfilariae in the peripheral blood varies with the
species and sometimes with the geographic area.

Question 29

For which of the following diseases is
close contact with an infected human host
the most important mechanism of
transmission?

A. Schistosomiasis
B. Toxoplasmosis
C. Trichinosis
D. Trichomoniasis

Answer 29

D. Sexual intercourse with infected men is
thought to be the most important mode of transmission of Trichomonas vaginalis to women.

Question 30

Which of the following helminths
produces an elongate, barrel-shaped egg
(50 X 22 |xm) with a colorless polar plug
at each end?

A. Ascaris lumbricoides
B. Hymenolepis nana
C. Necator americanus
D. Trichuris trichiura

Answer 30

D. Typical eggs of T. trichiura are yellow to
brown, with colorless polar plugs

Question 31

Which species of Plasmodium may
readily be identified when crescent-shaped
gametocytes are found in stained blood
films?

A. P. falciparum
B. P. malariae
C. P. ovale
D. P. vivax

Answer 31

A. The gametocytes of P. vivax, P. malariae,
and P. ovale are round and somewhat similar in
appearance.

Question 32

Cysts of Giardia lamblia

A. Contain four nuclei
B. Are motile by flagella
C. Have an undulating membrane
D. Are rarely found in stool specimens

Answer 32

A. The cysts of G. lamblia contain four nuclei
and are passed in the stool of infected animals.

Question 33

Migration of larva through the skin can
sometimes produce allergic reactions called
larva migrans; this is associated with

A. Strongyloides stercoralis
B. Dracunculus medinensis
C. Onchocerca volvulus
D. Loa loa

Answer 33

A. The life cycle of a number of human nematodes includes migration through the skin and
peripheral bloodstream. I

Question 34

A free-living ameba that causes primary
amebic meningoencephalitis is

A. Dientamoeba fragilis
B. Entamoeba coli
C. Entamoeba histolytica
D. Naegleria fowleri

Answer 34

D. Naegleria fowleri is found in freshwater
ponds and lakes, especially those with disturbed
or suspended soil.

Question 35

Decontamination of drinking water, fruits,
and vegetables before consumption is
necessary in countries without welldeveloped public sanitation. Which of the
following diseases would probably be
least affected by that kind of precaution?

A. Amebiasis
B. Ascariasis
C. Filariasis
D. Giardiasis

Answer 35

C. Infectious cysts of amebae and Giardia lamblia and eggs of Ascaris lumbricoides may all be
ingested in fecally contaminated water and/or on
fecally contaminated plants.

Question 36

Which stage of Taenia saginata is usually
infective for humans?

A. Cysticercus larva
B. Embryonated egg
C. Filariform larva
D. Rhabditiform larva

Answer 36

A. Humans are infected with T. saginata by eating beef containing live cysticerci, the infectious
larval stage of this parasite.

Question 37

This amebic cyst has an average size of
6-8 um and is usually spherical. When
mature, it has four nuclei, but immature
cysts with one or two nuclei are often
seen. The nuclei have fine uniform
granules of peripheral chromatin and
small, discrete, usually central
karyosomes. Chromatoidal bars with
bluntly rounded ends are sometimes
present. Name the species.

A. Endolimax nana
B. Entamoeba coli
C. Entamoeba hartmanni
D. Entamoeba histolytica

Answer 37

C. Cysts of E. hartmanni are differentiated from
cysts of E. histolytica by their small size; they are
otherwise morphologically identical. E. hartmanni, which was formerly called “small race
ameba,” is considered to be nonpathogenic.

Question 38

Which stage of Trichuris trichiura is
infective for humans?

A. Proglottid
B. Filariform larva
C. Rhabditiform larva
D. Embryonated ovum

Answer 38

D. The fertilized ova of T. trichiura are unsegmented when released, and embryonic development occurs outside of the host. In moist, warm,
shaded soil, the first-stage larva develops within
the egg in about 2 weeks.

Question 39

An intestinal parasite is seen in an iodinestained fecal wet mount that is described
as being 25 (Jim in diameter with a
homogenously stained central body
surrounded by a thin ring of cytoplasm
containing a number of nuclei. This best
describes

A. Blastocystis hominis
B. Endolimax nana
C. Entamoeba dispar
D. lodamoeba btitschlii

Answer 39

A. The most common form of B. hominis seen
in human feces is called the “classic form.” This
form contains a central body that was previously
thought to be a vacuole.

Question 40

Sanitary disposal of human feces is the
most important factor in decreasing the
incidence of most infections caused by
intestinal parasites. Which of the
following diseases would not be affected
by that kind of sanitation?

A. Ascariasis
B. Taeniasis
C. Trichinosis
D. Hookworm infection

Answer 40

C. Excretion in human feces of the eggs of the
hookworms, Taenia solium, T. saginata, and
Ascaris lumbricoid.es, is an essential or important factor in perpetuating the cycle of infection
with these parasites.

Question 41

Which species of Plasmodium is characterized by the presence of Schiiffner’s dots
in the infected erythrocytes?

A. Plasmodiumfalciparum
B. Plasmodium knowlesi
C. Plasmodium malariae
D. Plasmodium ovale

Answer 41

D. Typically, RBCs infected with P. ovale are larger than uninfected cells, pale and often misshapen, and frequently contain Schiiffner’s dots or stippling in any stage from young ring forms
onward.

Question 42

Which of the following is the largest
intestinal protozoa infecting humans?

A. Balantidium coli
B. Dientamoeba frag His
C. Entamoeba histolytica
D. Giardia lamblia

Answer 42

A. Balantidium coli is the largest intestinal protozoan infecting humans. Cysts range in size
from 43 to 65 jam, and the trophozoites are typically 50-100 jam in length and 40-70 jam in
width. Pigs seem to be the most important reservoir for B. coli.

Question 43

The rhabditiform larvae of Strongyloides
stercoralis

A. Mate and produce ova
B. Are infective for humans
C. Are the diagnostic form found in feces
D. Are found in the blood of infected
humans

Answer 43

C. The rhabditiform larvae of S. stercoralis are
the diagnostic stage typically passed in the feces
of infected persons. The larvae measure up to
380 um long X 20 urn wide.

Question 44

Which species of Plasmodium can have
exoerythrocytic stages capable of causing
relapses months or years after initial
infection?

A. P. falciparum
B. P. ovale
C. P. malariae
D. P. cynomolgi

Answer 44

B. A malaria relapse is parasitemia developing
from exoerythrocytic stages in the liver. These
persistent stages are found in P ovale and
P. vivax infections, and they may cause relapses
up to 4 or 5 years after the primary infection

Question 45

A Giemsa-stained thick blood film showed
many ring forms with no older stages, and
a number of the rings had double
chromatin dots. These findings are
characteristic of

A. Plasmodium falciparum
B. Plasmodium vivax
C. Plasmodium malariae
D. Plasmodium ovale

Answer 45

A. P falciparum infections tend to produce a
large number of rings that frequently have
double chromatin, which is only occasionally
found in other species. P. falciparum differs
from other plasmodia of humans in that only
early trophozoites (ring forms) and gametocytes
are found in peripheral blood except in severe
cases.

Question 46

Which of the following nematode
parasites is acquired from eating inadequately cooked, infected pork?

A. Strongyloides stercoralis
B. Taenia saginata
C. Taenia solium
D. Trichinella spiralis

Answer 46

D. T. spiralis is a nematode parasite whose
infectious larvae may be found encysted in the
muscles of flesh-eating mammals.

Question 47

Which of the following pairs of helminths
cannot be reliably differentiated by the
appearance of their eggs?

A. Ascaris lumbricoides and Necator
americanus
B. Hymenolepis nana and H. diminuta
C. Necator americanus and Ancylostoma
duodenale
D. Diphyllobothrium latum and Fasciola
hepatica

Answer 47

C. N. americanus and A. duodenale are two
species of hookworms infecting humans

Question 48

Which of the following forms of
Toxoplasma gondii are produced in
infected humans?

A. Bradyzoites
B. Macrogametes
C. Sporoblasts
D. Oocysts

Answer 48

A. The life cycle of T. gondii includes five forms or stages, but only bradyzoites and tachyzoites
appear in the tissue phase during human infections.

Question 49

Hematuria is a typical sign of human
infection caused by

A. Trypanosoma cruzi
B. Trichinella spiralis
C. Trichomonas vaginalis
D. Schistosoma haematobium

Answer 49

D. A common sign of S. haematobium infection
is the presence of blood in the urine. This is due
to the damage caused when the eggs break out of
the blood vessels of the vesicular plexus into the
bladder.

Question 50

Which of the following is the vector for
Babesia?

A. Fleas
B. Lice
C. Ticks
D. Mosquitoes

Answer 50

D. A common sign of S. haematobium infection
is the presence of blood in the urine. This is due
to the damage caused when the eggs break out of
the blood vessels of the vesicular plexus into the
bladder.

Question 51

Chagas disease (American trypanosomiasis) is caused by

A. Tiypanosoma brucei
B. Trypanosoma cruzi
C. Leishmania braziliensis
D. Dracunculus medinensis

Answer 51

B. Chagas disease is found throughout the
American continents. The infectious agent,
T. cruzi, is transmitted to humans by reduviid
bugs, primarily the triatomids. Chagas disease
can be acute or chronic.

Question 52

Which of the following is the preferred
anticoagulant for preparing blood smears
for diagnosing malaria?

A. EDTA
B. Heparin
C. Sodium citrate
D. Sodium fluoride

Answer 52

A. Collection of blood by finger stick is preferred for preparing blood smears for the detection
of malaria. When a venipuncture is performed, the preferred anticoagulant for malarial blood smears is EDTA (ethylenediaminetetraacetic
acid). Heparin can be used, but it may cause distortion of some parasite forms.