Question 1

Asexual amplification,called merogony,is associated with the life cycle of which organism?

Accepted Answer

Cryptosporidium infections begin with the ingestion of viable oocysts.Upon contact with gastric and duodenal fluids,four sporozoites are released from each oocyst.They invade the epithelial cells and develop to trophozoites,surrounded by a parasitophorous vacuole.Within the epithelial cells,trophozoites undergo two or three generations of asexual amplification,called merogony,leading to the formation of different types of meronts that contain four to eight merozoites.The latter differentiate into sexually distinct stages in a process called gametogony.

Question 2

Which of the following intestinal protozoa has no cyst stage,ranges from 9 to 12 µm in diameter,and has two nuclei in 60% of clinical specimens?

Accepted Answer

D.fragilis has no cyst stage and ranges from 9 to 12 µm.Two nuclei are observed in 60% of clinical specimens.

Question 3

When cooking meat,an internal temperature of ____°C must be reached to kill organisms such as Toxoplasma and Sarcocystis.

Accepted Answer

Cooking meat until an internal temperature of higher than 67°C is reached will kill Toxoplasma gondii tissue cysts in meat.This temperature should also kill tissue cysts of Sarcocystis in meat.

Question 4

The polar tubule,which is responsible for the entrance of infective sporoplasm into the host cell,is found in which of the following genera?

Accepted Answer

Enterocytozoon is classified as a microsporidia.Human microsporidial infections have been documented worldwide.Infection occurs with the ingestion or inhalation of the infective spores,from which the infective sporoplasm enters the host cell through the polar tubule.

Question 5

Outbreaks of infection with the organism Cyclospora are linked to contaminated raspberries,lettuce,and snow peas.The stain of choice to identify the oocysts in stool samples is:

Accepted Answer

Outbreaks of Cyclospora have been linked to contaminated water and various types of fresh produce (e.g. ,raspberries,basil,baby lettuce leaves,snow peas).Modified acid-fast stains result in the oocysts appearing light pink to deep red,and some will contain granules or have a bubbly appearance,which is described as wrinkled cellophane.

Question 6

An intestinal protozoan appeared 8 µm in diameter with a small,compact,centrally located karyosome.Four nuclei were observed in the mature cyst.The organism can be identified as:

Accepted Answer

The above characteristics describe the cyst stage of the intestinal protozoan E.hartmanni.

Question 7

A patient has amebic colitis.A microscopic examination reveals the following:
·18 µm in diameter
·Fine granules
·Centrally located karyosome
·Cytoplasm with a "ground-glass" appearance
·RBC inclusions
This protozoan can be identified as:

Accepted Answer

These characteristics are all associated with E.histolytica infections.

Question 8

Which of the following nonpathogenic protozoa has a very large glycogen vacuole in its cyst form and measures approximately 5 to 20 µm in diameter?

Accepted Answer

I.butschlii has a characteristically large glycogen vacuole in its cyst form.Although worldwide in distribution,it is a nonpathogenic amoeba.

Question 9

The drug of choice for the parasite Blastocystis hominis,which is believed to produce proteases and is considered a virulence factor responsible for its pathogenesis,is:

Accepted Answer

The organism B.hominis produces proteases,which have been suggested to add to its virulence.The drug of choice to treat B.hominis infections is metronidazole (Flagyl).

Question 10

This flagellate is pear-shaped with "falling leaf" motility.It contains variant-specific surface proteins (VSPs)on its surface,which provide a mechanism for the organism to survive in the small intestine as a result of its ability to resist intestinal proteases.The organism is:

Accepted Answer

The VSPs are a family of related,highly unusual proteins covering the surface of the organism.The VSPs are resistant to the effects of intestinal proteases,thus allowing the parasites to survive in the protease-rich small intestine.An antigenic variation of the surface antigen during human infections with G.duodenalis has been documented.

Question 11

The Cystoisospora belli organism,which contains two sporocysts with four sporozoites each,is recovered from fecal specimens and has also been implicated in traveler's diarrhea.The drug of choice to treat infection caused by C.belli is:

Accepted Answer

C.belli oocysts are passed in the feces unsporulated or partially sporulated.Oocysts complete sporulation within 72 hours,although it may take longer,depending on the temperature.Sporulated oocysts contain two sporocysts,each with four sporozoites.C.belli has also been implicated in traveler's diarrhea.The drug of choice to treat infection is a trimethoprim-sulfamethoxazole combination antibiotic,which is administered two to four times a day for 10 to 14 days.

Question 12

The organism Sarcocystis has an obligatory two-host life cycle-an intermediate host and definitive host.The sporocysts found in a stool specimen,which measure 9 to 16 µm,are broadly oval with slightly ___________ ends.

Accepted Answer

Sarcocystis has an obligatory two-host life cycle.Intermediate hosts,such as herbivores and omnivores,become infected through the ingestion of sporocysts excreted in the feces of definitive hosts,such as carnivores and omnivores.The sporocysts found in the stool are broadly oval,slightly tapered at the ends,measure 9 to 16 µm,and contain four mature sporozoites and the residual body.

Question 13

The cyst form of Balantidium coli is the infective stage.It has one large kidney-shaped macronucleus and one small,round micronucleus.The troph is quite large,measuring 50 to 150 µm in length and 40 to 70 µm in width.What single feature is associated with this organism?

Accepted Answer

B.coli trophs have one large kidney-shaped macronucleus and one small,round micronucleus,which is difficult to see,even in the stained smear.The macronucleus may be visible in an unstained preparation.The single feature associated with this organism is a body that is covered with cilia,which tend to be longer near the cytostome.Cytoplasm may be vacuolated.

Question 14

A patient is diagnosed with a severe intestinal disease caused by E.histolytica.Which of the following treatments should be administered?

Accepted Answer

In severe intestinal disease caused by E.histolytica,metronidazole plus one of the luminal drugs (e.g. ,iodoquinol,diloxanide furoate)should be used for therapy.

Question 15

Which of the following flagellates has a single nucleus in the cyst and the typical curved,cytostomal fibril,which is called a shepherd's crook?

Accepted Answer

C.mesnili contains a cytostome with supporting fibrils,which are usually visible in a stained preparation.A curved fibril along the side of the cytostome is usually referred to as a shepherd's crook.

Question 16

Highly active antiretroviral therapy (HAART)is the most effective prophylaxis and treatment in patients with acquired immunodeficiency syndrome (AIDS)with which type of infection?

Accepted Answer

In industrialized nations,the most effective prophylaxis and treatment for cryptosporidiosis in patients with AIDS is the use of HAART.The eradication and prevention of the infection are related to the replenishment of CD4+ cells in treated persons and the antiparasitic activities of the protease inhibitors used in HAART.A relapse of cryptosporidiosis is common in patients with AIDS who have stopped using HAART.

Question 17

E.coli,a protozoan that ranges from 15 to 25 µm in diameter,can contain up to eight nuclei in mature cysts.How would the karyosome expect to appear on a stained slide?

Accepted Answer

E.coli,which usually ranges from 15 to 25 µm in diameter,can contain eight nuclei in the mature cyst.The karyosome appears large,not compact,which may or may not be eccentric.

Question 18

The peripheral chromatin,which contains fine granules that are uniform in size and are evenly distributed,can be found in which one of the following protozoa?

Accepted Answer

The peripheral chromatin of the intestinal protozoan (amoeba),E.histolytica,contains fine granules that are uniform in size and are evenly distributed.It also possesses progressive fingerlike pseudopodia and rapid motility.

Question 19

A tissue sample is sent to the laboratory and microscopically examined for the presence of amebae.To differentiate between the host cells and the organism,_______ stain is used to allow the organisms to appear bright pink with a green-blue background.

Accepted Answer

A histologic diagnosis of amebiasis can be made when the trophozoites in the tissue are identified.Organisms must be differentiated from host cells,particularly histiocytes and ganglion cells.PAS staining is often used to help locate the organisms.The organisms will appear bright pink with a green-blue background,depending on the counterstain used.

Quiz 46: Intestinal Protozoa