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72 Cards in this Set

  • Front
  • Back
Four broad groups of intestinal protozoa
amoebae, flagellates, ciliates, and coccidia
Three genera of amoebae that may inhabit the human intestinal tract
Entamoeba, Iodamoeba, and Endolimax (last two generally considered nonpathogenic)
The only pathogenic amoeba for humans
Entamoebae histolytica
Entamoeba histolytica look-alikes include
E. hartmanni and E. dispar
E. histolytica is transmitted by___
Fecal-oral route
Mature cysts (infective stage) are ingested w/ contaminated food or water
E. histolytica
5-50% of people in endemic areas are carriers. What % will develop invasive, dysenteric disease and extraintestinal disease
10% will develop amebic dysentery

0.5% will develop extraintestinal disease (hepatic abscess) w/ 2-10% mortality rate
80% of E. histolytica infections are ___
E. histolytica

Typical colonic lesions are called __
"Button-hole" ulcers or flask-shaped ulcers

Once the organisms penetrate the mucosa, the lesions extend laterally within the submucosa because the organisms cannot penetrate the muscular wall
E. histolytica

Onset of extraintestinal amebiasis may be within __
Days, or delayed months to years following an acute dysentery
Amebic abscess in the liver is typically diagnosed by seeing __
Defect in the right lobe of the liver on CT scan
Characteristic feature used to identify an Entamoeba spp. in stool
"Entamoeba"-type nucleus with peripherally deposited chromatin

Not seen in Iodamoeba or Endolimax spp. These nuceli have a central karyosome with a clear halo, but no peripherally placed chromatin - "ball in socket"
Feature seen in stool trophozoites that is virtually diagnostic of E. histolytica

When seen in stool - is predictive of an invasive strain
Entamoeba-type cysts with more than 4 nuclei rules out ___
E. histolytica
Serologic testing for invasive amebiasis is available, and is both ___ and ___
Sensitive and specific for invasive disease

Detection of specific surface protein on pathogenic strians of E. histolytica
Nonpathogenic E. histolytica is known as ___
E. dispar
Morphologic identification of E. histolytica/dispar in stool should be followed by ___
Antigen-detection or PCR-based testing to differentiate the two

The majority of patients will NOT require treatment (E. dispar)

Only about 10% will be found to be pathogenic (E. histolytica)
Antigen-detection and PCR-based techniques are available for the identification of E. histolytica in preserved stool specimens

Which test is specific for E. histolytica
TechLab product is the only test that is specfic for E. histolytica
Iodamoeba butschlii cysts can be distinguished from Entamoeba spp by __
"Ball in socket" nucleus

large, iodine positive glycogen vacuole
Entamoeba hartmanni is distinguished from E. histolytica base on __

It is smaller
Endolimax nana is distinguished from E. histolytica based on ___
"Ball in socket" nucleus
Small size
Entamoeba coli is distinguished from E. histolytica by ___
Lack of erythrophagocytosis

Typically bigger cysts and trophozoites (but there is overlap)

The ring of chromatin is more blotchy in distribution instead of evenly dispersed and beadlike, as it is for E. histolytica
Intestinal flagellates most commonly seen in human stool specimens include
Giardia lamblia
Chilomastix mesnili
Dientamoeba fragilis
Trichomonas spp.
Structures seen in flagellates include __
Kinetoplast (flagella attach to)
Parabasal bodies
Morphologic features of Giardia lamblia
"Monkey face"
- Bilaterally symmetrical
- Two nuclei separate by a central axostyle
- Two median parabasal bodies located on either side of the axostyle "mustache"
- Graceful "falling leaf" motility
- Sucking disk on ventral surface

- Mature cysts have double complement of strucutres (4 nuclei, four median bodies)
Giardia lamblia cyst nuclei are distinguished from those of the Entamoebae by __
No peripheral chromatin displacement
G. lamblia
Triple fecal test has sensitivity of ___
Three stool specimens on nonconsecutive days

If G. lamblia is highly suspected, and the fecal speciemns are not diagnostic, then ___
1. Enterotest - string test; takes about 5 hours

More invasive procedures could be utilized:
- duodenal biopsy
- duodenal aspirate
Direct immunofluorescence detection for G. lamblia has a reported sensitivity and specificity of
100% and 100%

Not uncommonly, it can detect organisms not observed by rountine O&P examination
The current test of choice for diagnosing Giardiasis is
Antigen detection assays

- greater sensitivity over routine microscopy
- includes DFAs, EIAs, and three rapid immunochromatographic assays
Chilomastix mesnili are intestinal flagellates that are considered ____, but ___
Nonpathogenic, but are acquired by ingestion of feces-contaminated food and water
Chilomastix mesnili

Morphologic features of the trophozoite and cyst forms
- Pear-shaped
- One nucleus located adjacent to the outer membrane

- Pear to lemon-shaped
- One nucleus
- Shepards crook - curved cytstome is diagnositic when seen
- hyaline knob off to one side of cyst
Dientamoeba fragilis is classified as a __
Flagellate, despite the lack of flagella by light microscope

Typically appears as an amebic trophozoite
Dientamoeba fragilis has fragile cytoplasm, therefore, identification in stool requires __
Examination of fixed specimens. The organism is difficult to see in wet mounts
What does the cyst stage of Dientamoeba fragilis look like?
There is NO cyst stage!
Only trophozoites
Morphologic features of Dientamoeba fragilis trohozoites
- asymmetrical "ameboid" forms
- two nuclei, with prominent karyosomes that are fragmented into 4-8 granules (may be hard to see)
- broad-lobed, clear pseudopods
Dientamoeba fragilis lacks a cyst stage, so it is not likely to be transmitted by food or waterborne transfer, instead ___
Likely transmitted by infected Enterobius vermicularis eggs

There is a 9-fold higher incidence of D. fragilis infection in patients with pinworms
Is it Trichimonis hominis or Trichimonis vaginalis in the stool wet mount?
T. hominis is a nonpathogenic flagellate found in stool specimens

T. vaginalis is from the vagina

But, T. vaginalis could contaminate a stool specimen
The infective stage of G. lamblia is ___
Capable of long-term survival in the environment

Humans infected by consuming contaminated water or poorly washed fresh foods.
Which stage(s) of Giardia lamblia are present in the stool
Cysts and trophozoites
G. lamblia cysts, once ingested, excysts in the ___
Duodenum, where they live and divide by longitudinal binary fission
Features that distinguish Trichimonis hominis from Chilomastix mesnili
Both are nonpathogenic!
The nucleus of T.hominis is not adjacent to the outer membrane
The only pathogenic ciliate
Balantidium coli
Key morphologic features of Balantidium coli trophozoite and cyst
- anterior cytostome
- circumferential cilia
- large rod- or horeshoe-shaped macronucleus

- characteristic dumbbell shaped macronucleus
- cilia are within the cyst
B. coli is transmitted by __ and is associated with ___
Feca-oral route (Human Balantidiosis)

Human Balantidioisis is typically __
Noninvasive, asymptomatic, and self-limited

In debilitated patients with a heavy load - bloody dysentery, severe dehydration, and rarely death
Coccidia are __
Obligate tissue parasites
Blood: Plasmodium spp.
Tissues: Toxoplasma gondii
- Isospora belli
- Cyrptosporidium spp.
- Cyclospora spp.
- Sarcocystis spp.
Isospora belli is unique among the coccidia in that it does not require __
an intermediate host for sexual reproduction, both the sexual and asexual stages can occur in the human

the other coccidia require an intermediate host (cat, calf,....)
Cryptosporidia are ____ that infect domestic animals such as pigs, calves, and chickens

Humans are infected by __
minute coccidian protozoa

contact with infected animals or ingesting fecally contaminated food or water
Detection of Cryptosporidium or Isospora in any patient in whom AIDS is not suspected should lead to __
HIV testing
Cryptosporidium transmision by waterborne route is problematic because __
it is not eliminated by chlorination
All stages of development of Cyrptosporidium parvum are confined to ___
the microvilli of the intestinal epithelium

tiny aggregates of oocysts attached to the epithelial surface of villi are seen on H&E biopsy tissue
Oocysts of C. parvum efface the __ leading to __
brush border of intestinal lining cells

loss of microvilli leads to impaired digestion, malabsorption, and diarrhea
In immunocompetent persons, C. parvum causes ___

In immunocompromised it causes __
- cholera-like watery diarrhea or mucous diarrhea
- gastroenteritis +/- vomiting
- malabsorption
- low grade fever
- self-limited 7-14 days

- prolonged course with severe watery diarrhea
- may last months
- requires aggress treatment, especially if CD4 count <200
Treatment of cryptosporidiosis in AIDS patients
No good treatment regimens

Organisms may be sheltered from the effects of antimicrobials by parasitophorous vacuoles that are formed within the host cells

Treatment includes attempts to partially restore immune function with antiretroviral therapy
Diagnosis of cyrptosporidiosis is made by __
detection of oocysts in fecal specimens

oocysts are small (5-6 microns)
C. parvum can be better detected in stool specimens using
1. modified acid-fast stain: red-pink, homogenous, 5-6 micron oocysts
2. Immunoassays
3. Immunofluorescence techniques
4. PCR-based techniques
Cyclospora cayetanensis is a ____ protozoan that causes ___
Coccidian protozoan (obligate intracellular parasite)

Immunocompentent - causes a self-limited diarrheal illness

Immunocompromised - causes prolonged noninvasive diarrheal disease (4-6 weeks), may mimic sprue, may be associated with biliary disease
Cryptosporidium, Cyclospora, and Isospora are all mostly diseases of
AIDS patients
Seeing Isospora belli and Cryptosporidium in the same stool specimen suggests __
Possible HIV infection
Mature oocysts of Isospora contain ___ sporocysts
Isospora is unique among the coccidian protozoa in that it does not require ___
an intermediate host to complete its sexual reproductive cycle; both sexual and asexual stages occur in the human
Sarcocystis is a ___ that infects ___ and ___
Coccidian protozoan that infects humans and other mammals
Sarcocystis is unique among the coccidian protozoan in that it can utilize humans as either a ___ or ___ host
Intermediate or definitive host

The second host is another mammal
Humans as an intermediate host for Sarcocystis infection is due to
Ingestion of oocysts from animal stool sources (contaminated food or water)

Sarcocysts develop in the human host skeletal muscle (usually asymptomatic)
Sarcocysts seen in muscle tissue are 100 x 300 microns and contain numerous inactive spherical bradyzoites
Humans as the definitive host for Sarcocystis infection is due to

The organism undergos ____ reproduction, leading to the production of _____
Ingestion of undercooked beef or pork

The sexual cycle of the organism takes place in the subepithelium of the small bowel mucosa

Often asymptomatic

Diagnostic oval oocysts are seen in stool, and they resemble those of Isospora but are smaller
Microsoprum is a separate phylum consisting of protozoa that __
Produce tiny spores (2 micron) that possess a complex tubular structure used to inject infectious sporoplasm into host cells
Microsporidium spp is a collective group of species that primarily infect nonhumans
Only 4 genera, within the phylum, infect humans
Microsporidia spores can be seen in histologic sections as __
Tiny (2 micron) spores located within enterocytes between the nucleus and the luminal surface

They are better visualized with PAS, GMS, acid-fast, modified trichrome or Giemsa stains
Electron micrographs of microsporidia would demonstrate __
The characterisitic polar tube seen in all genera
In stool specimens, stained microsporidia exhibit a characteristic __
Transverse pink-stained band midway in the cells
Intestinal coccidian protoza cause signficiant disease primarily in __
AIDS patients

Isospora belli
Microsporidium spp are ____
Obligate intracellular parasites

Protozoa that use a polar tube to inject the infectious sporoplasm into host cells, such as enteroctyes

They can cause disseminated disease as well, involving multiple organ systems