Parasitology - Intestinal Protozoa

Front 1

Four broad groups of intestinal protozoa

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amoebae, flagellates, ciliates, and coccidia

Front 2

Three genera of amoebae that may inhabit the human intestinal tract

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Entamoeba, Iodamoeba, and Endolimax (last two generally considered nonpathogenic)

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The only pathogenic amoeba for humans

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Entamoebae histolytica

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Entamoeba histolytica look-alikes include

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E. hartmanni and E. dispar

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E. histolytica is transmitted by___

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Fecal-oral route
Mature cysts (infective stage) are ingested w/ contaminated food or water

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E. histolytica
5-50% of people in endemic areas are carriers. What % will develop invasive, dysenteric disease and extraintestinal disease

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10% will develop amebic dysentery

0.5% will develop extraintestinal disease (hepatic abscess) w/ 2-10% mortality rate

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80% of E. histolytica infections are ___

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Asymptomatic

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E. histolytica

Typical colonic lesions are called __

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"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

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E. histolytica

Onset of extraintestinal amebiasis may be within __

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Days, or delayed months to years following an acute dysentery

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Amebic abscess in the liver is typically diagnosed by seeing __

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Defect in the right lobe of the liver on CT scan

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Characteristic feature used to identify an Entamoeba spp. in stool

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"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"

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Feature seen in stool trophozoites that is virtually diagnostic of E. histolytica

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Erythrophagocytosis

When seen in stool - is predictive of an invasive strain

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Entamoeba-type cysts with more than 4 nuclei rules out ___

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E. histolytica

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Serologic testing for invasive amebiasis is available, and is both ___ and ___

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Sensitive and specific for invasive disease

Detection of specific surface protein on pathogenic strians of E. histolytica

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Nonpathogenic E. histolytica is known as ___

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E. dispar

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Morphologic identification of E. histolytica/dispar in stool should be followed by ___

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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)

Front 17

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

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TechLab product is the only test that is specfic for E. histolytica

Front 18

Iodamoeba butschlii cysts can be distinguished from Entamoeba spp by __

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"Ball in socket" nucleus

large, iodine positive glycogen vacuole

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Entamoeba hartmanni is distinguished from E. histolytica base on __

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Size

It is smaller

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Endolimax nana is distinguished from E. histolytica based on ___

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"Ball in socket" nucleus
Small size

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Entamoeba coli is distinguished from E. histolytica by ___

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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

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Intestinal flagellates most commonly seen in human stool specimens include

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Giardia lamblia
Chilomastix mesnili
Dientamoeba fragilis
Trichomonas spp.

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Structures seen in flagellates include __

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Flagella!
Kinetoplast (flagella attach to)
Axostyle
Parabasal bodies

Front 24

Morphologic features of Giardia lamblia

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TROPHOZOITES:
"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

CYSTS:
- Mature cysts have double complement of strucutres (4 nuclei, four median bodies)

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Giardia lamblia cyst nuclei are distinguished from those of the Entamoebae by __

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No peripheral chromatin displacement

Front 26

G. lamblia
Triple fecal test has sensitivity of ___

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Three stool specimens on nonconsecutive days

95.7%

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If G. lamblia is highly suspected, and the fecal speciemns are not diagnostic, then ___

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1. Enterotest - string test; takes about 5 hours

More invasive procedures could be utilized:
- duodenal biopsy
- duodenal aspirate

Front 28

Direct immunofluorescence detection for G. lamblia has a reported sensitivity and specificity of

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100% and 100%

Not uncommonly, it can detect organisms not observed by rountine O&P examination

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The current test of choice for diagnosing Giardiasis is

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Antigen detection assays

- greater sensitivity over routine microscopy
- includes DFAs, EIAs, and three rapid immunochromatographic assays

Front 30

Chilomastix mesnili are intestinal flagellates that are considered ____, but ___

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Nonpathogenic, but are acquired by ingestion of feces-contaminated food and water

Front 31

Chilomastix mesnili

Morphologic features of the trophozoite and cyst forms

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TROPHOZOITES:
- Pear-shaped
- One nucleus located adjacent to the outer membrane

CYSTS:
- Pear to lemon-shaped
- One nucleus
- Shepards crook - curved cytstome is diagnositic when seen
- hyaline knob off to one side of cyst

Front 32

Dientamoeba fragilis is classified as a __

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Flagellate, despite the lack of flagella by light microscope

Typically appears as an amebic trophozoite

Front 33

Dientamoeba fragilis has fragile cytoplasm, therefore, identification in stool requires __

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Examination of fixed specimens. The organism is difficult to see in wet mounts

Front 34

What does the cyst stage of Dientamoeba fragilis look like?

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There is NO cyst stage!
Only trophozoites

Front 35

Morphologic features of Dientamoeba fragilis trohozoites

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- asymmetrical "ameboid" forms
- two nuclei, with prominent karyosomes that are fragmented into 4-8 granules (may be hard to see)
- broad-lobed, clear pseudopods

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Dientamoeba fragilis lacks a cyst stage, so it is not likely to be transmitted by food or waterborne transfer, instead ___

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Likely transmitted by infected Enterobius vermicularis eggs

There is a 9-fold higher incidence of D. fragilis infection in patients with pinworms

Front 37

Is it Trichimonis hominis or Trichimonis vaginalis in the stool wet mount?

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T. hominis is a nonpathogenic flagellate found in stool specimens

T. vaginalis is from the vagina

But, T. vaginalis could contaminate a stool specimen

Front 38

The infective stage of G. lamblia is ___

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Cysts
Capable of long-term survival in the environment

Humans infected by consuming contaminated water or poorly washed fresh foods.

Front 39

Which stage(s) of Giardia lamblia are present in the stool

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Cysts and trophozoites

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G. lamblia cysts, once ingested, excysts in the ___

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Duodenum, where they live and divide by longitudinal binary fission

Front 41

Features that distinguish Trichimonis hominis from Chilomastix mesnili

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Both are nonpathogenic!
The nucleus of T.hominis is not adjacent to the outer membrane

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The only pathogenic ciliate

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Balantidium coli

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Key morphologic features of Balantidium coli trophozoite and cyst

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TROPHOZOITE:
- anterior cytostome
- circumferential cilia
- large rod- or horeshoe-shaped macronucleus

CYSTS:
- characteristic dumbbell shaped macronucleus
- cilia are within the cyst

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B. coli is transmitted by __ and is associated with ___

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Feca-oral route (Human Balantidiosis)

Pigs

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Human Balantidioisis is typically __

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Noninvasive, asymptomatic, and self-limited

In debilitated patients with a heavy load - bloody dysentery, severe dehydration, and rarely death

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Coccidia are __

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Obligate tissue parasites
Include:
Blood: Plasmodium spp.
Tissues: Toxoplasma gondii
Intestinal:
- Isospora belli
- Cyrptosporidium spp.
- Cyclospora spp.
- Sarcocystis spp.

Front 47

Isospora belli is unique among the coccidia in that it does not require __

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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,....)

Front 48

Cryptosporidia are ____ that infect domestic animals such as pigs, calves, and chickens

Humans are infected by __

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minute coccidian protozoa

contact with infected animals or ingesting fecally contaminated food or water

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Detection of Cryptosporidium or Isospora in any patient in whom AIDS is not suspected should lead to __

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HIV testing

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Cryptosporidium transmision by waterborne route is problematic because __

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it is not eliminated by chlorination

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All stages of development of Cyrptosporidium parvum are confined to ___

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the microvilli of the intestinal epithelium

tiny aggregates of oocysts attached to the epithelial surface of villi are seen on H&E biopsy tissue

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Oocysts of C. parvum efface the __ leading to __

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brush border of intestinal lining cells

loss of microvilli leads to impaired digestion, malabsorption, and diarrhea

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In immunocompetent persons, C. parvum causes ___

In immunocompromised it causes __

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Immunocompetent:
- cholera-like watery diarrhea or mucous diarrhea
- gastroenteritis +/- vomiting
- malabsorption
- low grade fever
- self-limited 7-14 days

AIDS:
- prolonged course with severe watery diarrhea
- may last months
- requires aggress treatment, especially if CD4 count <200

Front 54

Treatment of cryptosporidiosis in AIDS patients

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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

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Diagnosis of cyrptosporidiosis is made by __

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detection of oocysts in fecal specimens

oocysts are small (5-6 microns)

Front 56

C. parvum can be better detected in stool specimens using

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1. modified acid-fast stain: red-pink, homogenous, 5-6 micron oocysts
2. Immunoassays
3. Immunofluorescence techniques
4. PCR-based techniques

Front 57

Cyclospora cayetanensis is a ____ protozoan that causes ___

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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

Front 58

Cryptosporidium, Cyclospora, and Isospora are all mostly diseases of

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AIDS patients

Front 59

Seeing Isospora belli and Cryptosporidium in the same stool specimen suggests __

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Possible HIV infection

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Mature oocysts of Isospora contain ___ sporocysts

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Two

Front 61

Isospora is unique among the coccidian protozoa in that it does not require ___

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an intermediate host to complete its sexual reproductive cycle; both sexual and asexual stages occur in the human

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Sarcocystis is a ___ that infects ___ and ___

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Coccidian protozoan that infects humans and other mammals

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Sarcocystis is unique among the coccidian protozoan in that it can utilize humans as either a ___ or ___ host

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Intermediate or definitive host

The second host is another mammal

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Humans as an intermediate host for Sarcocystis infection is due to

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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

Front 65

Humans as the definitive host for Sarcocystis infection is due to

The organism undergos ____ reproduction, leading to the production of _____

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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

Front 66

Microsoprum is a separate phylum consisting of protozoa that __

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Produce tiny spores (2 micron) that possess a complex tubular structure used to inject infectious sporoplasm into host cells

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Microsporidium spp is a collective group of species that primarily infect nonhumans

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Only 4 genera, within the phylum, infect humans

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Microsporidia spores can be seen in histologic sections as __

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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

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Electron micrographs of microsporidia would demonstrate __

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The characterisitic polar tube seen in all genera

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In stool specimens, stained microsporidia exhibit a characteristic __

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Transverse pink-stained band midway in the cells

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Intestinal coccidian protoza cause signficiant disease primarily in __

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AIDS patients

Cryptosporidium
Isospora belli
Cyclospora

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Microsporidium spp are ____

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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