SUCCESS In Clinical Laboratory Science
Parasitology
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 - answersA. Because the eggs of E. vermicularis are usually
deposited on the perianal area, cellulose tape slides are recommended for collecting the
eggs. Recovery is best if specimens are collected late in the evening or before bathing
or defecating in the morning. The gravid female worms usually migrate at night to the
perianal region to deposit eggs. Because their migration is sporadic, several
consecutive collections may be necessary to detect the infection.
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 - answersD. 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. These cysts are most often in
the liver or lung. Although clinical findings can provide a presumptive diagnosis, this is
best confirmed by the finding, at surgery, of encysted larval scolices. Each scolex is
capable of developing into an adult worm after ingestion by a dog or related animal, the
definitive host.
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. - answersC.
Fresh liquid stools are more likely to contain motile protozoan trophozoites that can be
detectedin saline wet mounts. Urine in stool specimens can damage parasite
morphology, as does freezing. Unpreserved stool specimens should only be left at room
temperature up to a couple of hours before examining or placing into a preservative.
Cysts are the infective stage of this intestinal flagellate.
A. Balantidium coli
B. Dientamoebafragilis
C. Entamoeba coli
,D. Giardia lamblia - answersD. 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. However, D. fragilis does not have a cyst stage. G. lamblia is the only
flagellate in the list of protozoa with a cyst stage. B. coli is a ciliate and E. coli is an
ameba.
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 - answersA. Although T. spiralis adults live in the intestinal
mucosa, they are rarely seen. The female deposits living larvae into the mucosa or
lymphatic vessels, from which they normally enter the bloodstream and are
disseminated throughout the body. They then burrow into muscle fibers. Although larvae
may occasionally be liberated into the intestinal lumen, the definitive diagnostic
procedure is the demonstration of larvae in skeletal muscle, not in feces.
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 - answersB. 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. The
intermediate host is the host in which the asexual stage of the parasite is found. Vectors
are arthropods, like mosquitoes and ticks that transmit infectious agents. A commensal
is an organism that benefits from an existence with a host but does not damage the
host.
Species identification of an immature amebic cyst can be very difficult. The presence of
a large glycogen mass is sometimes seen in
A. Dientamoeba fragilis
B. Endolimax nana
C. Entamoeba coli
D. Entamoeba histolytica - answersC. Young cysts of E. coli can have a large glycogen
mass that pushes two nuclei to the outer edge of the cell. No cyst stage is known for D.
fragilis. The cysts of E. nana and E. histolytica do not contain glycogen.
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 - answersA. Mature cysts of I. biitschlii are usually ovoid, with
a single nucleus with a large eccentric karyosome. The cytoplasm contains a compact
, mass of glycogen, which appears as a clear area in unstained or permanently stained
preparations but stains dark brown with iodine. Chromatoid bodies are not present.
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 - answersD. E. histolytica
and E. dispar cannot be morphologically differentiated. The cyst stage of both
organisms has four nuclei with a centrally located karyosome. E. histolytica is a
wellrecognized intestinal parasite, whereas E. dispar is considered nonpathogenic.
Immunologic assays to detect antigens or molecular biology assays are necessary to
differentiate these two species.
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 - answersA. Although the condition may vary from patient to patient,
eosinophilia is often found in association with infections with tissue invading nematodes.
Eosinophilia of 40-80% is not unusual in trichinosis and in visceral larva migrans. It may
also be present in strongyloidiasis, early in Ascaris and hookworm infections, and in
filariasis, which may also cause pulmonary eosinophilia.
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 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 follow -
answersB. The symptoms and history for this patient are compatible with
trypanosomiasis (African sleeping sickness) caused by T. brucei. The trypomastigote
form of the parasite was found in peripheral blood smears from this patient. Another key
clinical sign is the presence of swollen lymph nodes at the posterior base of the neck;
this is called Winterbottom's sign
Which species of malaria parasite usually has ameboid trophozoites and produces
small reddish dots in the red blood cell cytoplasm?
Parasitology
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 - answersA. Because the eggs of E. vermicularis are usually
deposited on the perianal area, cellulose tape slides are recommended for collecting the
eggs. Recovery is best if specimens are collected late in the evening or before bathing
or defecating in the morning. The gravid female worms usually migrate at night to the
perianal region to deposit eggs. Because their migration is sporadic, several
consecutive collections may be necessary to detect the infection.
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 - answersD. 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. These cysts are most often in
the liver or lung. Although clinical findings can provide a presumptive diagnosis, this is
best confirmed by the finding, at surgery, of encysted larval scolices. Each scolex is
capable of developing into an adult worm after ingestion by a dog or related animal, the
definitive host.
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. - answersC.
Fresh liquid stools are more likely to contain motile protozoan trophozoites that can be
detectedin saline wet mounts. Urine in stool specimens can damage parasite
morphology, as does freezing. Unpreserved stool specimens should only be left at room
temperature up to a couple of hours before examining or placing into a preservative.
Cysts are the infective stage of this intestinal flagellate.
A. Balantidium coli
B. Dientamoebafragilis
C. Entamoeba coli
,D. Giardia lamblia - answersD. 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. However, D. fragilis does not have a cyst stage. G. lamblia is the only
flagellate in the list of protozoa with a cyst stage. B. coli is a ciliate and E. coli is an
ameba.
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 - answersA. Although T. spiralis adults live in the intestinal
mucosa, they are rarely seen. The female deposits living larvae into the mucosa or
lymphatic vessels, from which they normally enter the bloodstream and are
disseminated throughout the body. They then burrow into muscle fibers. Although larvae
may occasionally be liberated into the intestinal lumen, the definitive diagnostic
procedure is the demonstration of larvae in skeletal muscle, not in feces.
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 - answersB. 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. The
intermediate host is the host in which the asexual stage of the parasite is found. Vectors
are arthropods, like mosquitoes and ticks that transmit infectious agents. A commensal
is an organism that benefits from an existence with a host but does not damage the
host.
Species identification of an immature amebic cyst can be very difficult. The presence of
a large glycogen mass is sometimes seen in
A. Dientamoeba fragilis
B. Endolimax nana
C. Entamoeba coli
D. Entamoeba histolytica - answersC. Young cysts of E. coli can have a large glycogen
mass that pushes two nuclei to the outer edge of the cell. No cyst stage is known for D.
fragilis. The cysts of E. nana and E. histolytica do not contain glycogen.
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 - answersA. Mature cysts of I. biitschlii are usually ovoid, with
a single nucleus with a large eccentric karyosome. The cytoplasm contains a compact
, mass of glycogen, which appears as a clear area in unstained or permanently stained
preparations but stains dark brown with iodine. Chromatoid bodies are not present.
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 - answersD. E. histolytica
and E. dispar cannot be morphologically differentiated. The cyst stage of both
organisms has four nuclei with a centrally located karyosome. E. histolytica is a
wellrecognized intestinal parasite, whereas E. dispar is considered nonpathogenic.
Immunologic assays to detect antigens or molecular biology assays are necessary to
differentiate these two species.
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 - answersA. Although the condition may vary from patient to patient,
eosinophilia is often found in association with infections with tissue invading nematodes.
Eosinophilia of 40-80% is not unusual in trichinosis and in visceral larva migrans. It may
also be present in strongyloidiasis, early in Ascaris and hookworm infections, and in
filariasis, which may also cause pulmonary eosinophilia.
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 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 follow -
answersB. The symptoms and history for this patient are compatible with
trypanosomiasis (African sleeping sickness) caused by T. brucei. The trypomastigote
form of the parasite was found in peripheral blood smears from this patient. Another key
clinical sign is the presence of swollen lymph nodes at the posterior base of the neck;
this is called Winterbottom's sign
Which species of malaria parasite usually has ameboid trophozoites and produces
small reddish dots in the red blood cell cytoplasm?
