MODULE 2 UNIT 2 Flashcards
It includes the amoebas, which have no permanent locomotory organs, but move about with the aid of temporary prolongations of the body called
It includes those protozoa which possess whip-like structures called
Two groups of amoebae are of medical importance.
- Parasitic amoebae; 2. Pathogenic free-living amebae
three genera of Parasitic amoebae
Entamoeba, Endolimax, and Iodamoeba
Parasitic amoebae include
Entamoeba histolytica, Entamoeba dispar, Entamoeba coli, Entamoeba hartmanni, Endolimax nana, and Iodamoeba butschlii which are all found in the intestinal lumen, and Entamoeba gingivalis which is found in the mouth
is the only pathogenic species which causes intestinal and extraintestinal amoebiasis.
E. histolytica
All the other amaebae species are commensals. They all exist in two forms in the life cycle, trophozoites and cysts, EXCEPT {?} which occurs in the trophozoite stage only
E. gingivalis
Several species of free-living amoebae are found in soil and water.
Pathogenic free-living amebae
are of clinical interest because they can cause fatal meningoencephalitis and eye infections.
(1) Naegleria and (2) Acanthamoeba
Trophozoite Size
10-60 µm (ave: 15-20 µm)
Trophozoite Motility and
Pseudopodia
Progressive, rapid, unidirectional motility; with hyaline, fingerlike pseudopodia formed rapidly
Trophozoite Nucleus
Number
1
Trophozoite Peripheral
chromatin
Fine granules, uniform in size and usually evenly distributed; may have beaded appearance
Trophozoite Karyosome
Small, compact, centrally located
Trophozoite Linin network
The space between the karyosome and the nuclear membrane is traversed by fine thread of linin network giving a radial spokeswheel or cartwheel appearance.
Trophozoite Cytoplasm
Appearance
Finely granular, “ground-glass” appearance; clear differentiation into a clear ectoplasm and more granular endoplasm; if present, vacuoles are usually very small
Trophozoite Inclusions
RBCs are diagnostic; few ingested bacteria or debris in vacuoles
Cyst Size
10-20 µm (12-15 µm)
Cyst Shape
Usually spherical
Cyst Nucleus
Number
1-4; mature cyst contains 4 nuclei
Cyst Peripheral chromatin
Similar to that seen in trophozoite
Cyst Karyosome
Similar to that seen in trophozoite
Cyst Cytoplasm
Chromatoidal bodies
May be present; usually elongate with blunt, rounded, smooth ends (cigarshaped); may be round or oval.
Cyst Glycogen vacuole
May be present, usually diffuse, stains reddish brown with iodine.
is morphologically indistinguishable from E. histolytica and should be reported as E. histolytica/E. dispar unless ingested red blood cells are seen, suggesting E. histolytica infection.
Entamoeba dispar
The DNA and ribosomal RNA , and isoenzyme pattern of (?) is different from that of E. histolytica.
E. dispar
Unlike E. histolytica, E. dispar is (?).
nonpathogenic.
The ratio of E. dispar to E. histolytica in most developing countries can be as high as (?) in a community setting.
10:1
The ratio of E. dispar to E. histolytica in most developing countries can be as high as (?) in a community setting.
10:1
E. histolytica passes its life cycle in one host and has the following successive stages:
cyst, metacyst, metacystic trophozoite, trophozoite, and precyst.
are passed in feces
Cysts and trophozoites
Infection with Entamoeba histolytica (and E.dispar) occurs via (?) from fecally contaminated
food, water, or hands.
ingestion of quadrinucleated mature cysts
(?) occurs in the cecum or lower part of the ileum, under the influence of neutral or slightly acidic digestive juices.
Excystation
A quadrinucleated (?) is liberated from the cyst wall. The nuclei in the metacyst immediately undergo division to form eight nuclei, each of which gets surrounded by its own cytoplasm. The cytoplasm divides into as may parts as there are nuclei.
metacyst
(?) are released, which migrate to the large intestine (cecum), their normal habitat.
Eight (8) metacystic trophozoites (or amoebulae)
t. In the glandular crypts, they feed and grow and develop into normal (?)
trophozoites
The trophozoite discharges undigested food and condenses into a spherical mass, called the (?)
precyst
There are 2 types of inclusions in unripe and ripening cysts:
chromatoidal bodies and glycogen mass
s. Ripening of cysts of E. histolytica consists of (?) consecutive mitotic divisions of the nucleus to produce (?) nuclei .
2; 4
During this process,(?) is expended and the chromatoidal bodies become less conspicuous or completely disappear
glycogen
(?) are typically found in formed stool, whereas trophozoites are typically found in diarrheal stool.
Cysts
is used clinically to denote all conditions produced in human host by infection with E. histolytica at different areas of invasion.
Amoebiasis
E. hislolytica causes 2
(1) intestinal and (2) extraintestinal amoebiasis
Adapted by the WHO, intestinal amoebiasis is clinically classified into (a) asymptomatic, and (b) symptomatic infections.
Intestinal amoebiasis
intestinal amoebiasis is clinically classified into (?)
(a) asymptomatic, and (b) symptomatic infections.
The majority of infections with E. histolytica are
Asymptomatic infection
This occurs in approximately 90% of cases especially in endemic communities
Asymptomatic infection
There is NO evidence of tissue invasion.
Asymptomatic infection
Infected individual passes formed stool with cyst forms. But, there is concern that an infection with E. histolytica may become symptomatic in the intestinal tract or with subsequent extraintestinal invasion.
Asymptomatic infection
Only about 10% of amoebiasis are symptomatic
Symptomatic infection
(?) is defined as an intestinal infection caused by the presence of E. histolytica exhibiting symptoms occurs when the mucosa is invaded.
Amoebic colitis
(?) is defined as an intestinal infection caused by the presence of E. histolytica exhibiting symptoms occurs when the mucosa is invaded.
Amoebic colitis
(?) is characterized by gradual or sudden onset, dysentery with 6-10 or more bloodtinged, mucoid, foul-smelling stools per day.
Acute amoebic colitis or amoebic dysentery
(?) may resemble bacillary dysentery, but can be differentiated on clinical and laboratory grounds.
Amoebic dysentery
(?) does not always result in dysentery.
Intestinal amebiasis
(?) is uncommon (only if rectum is involved), low-grade fever or none at all, and mild leukocytosis.
Tenesmus
(?), aka nondysenteric amoebic colitis, is characterized by intermittent diarrhea and constipation. i.e., alternating diarrhea and constipation, or abdominal pain.
Chronic amoebic colitis
Cysts are found in formed stool while trophozoites are seen during times of diarrhea. This may last for years.
Chronic amoebic colitis
(?) got its name through its ability to lyze tissues, initiated by invasion of the colonic mucosa.
E. histolytica
There are three pathogenic processes, each of which is facilitated by the expression of virulence factor.
Cytoadherence; Cytolysis; Proteolysis
Trophozoite lectins, a group of proteins, bind to specific carbohydrate-containing receptors on host luminal surfaces and mediate adherence.
Cytoadherence
Amoebapores are proteins of amoeba capable of inserting into the host cell membrane and form pores causing lysis of the host cells. Trophozoites’ amoeboid movement also contributes to the lysis of mucosal cells.
Cytolysis.
Amoebapores are proteins of amoeba capable of inserting into the host cell membrane and form pores causing lysis of the host cells. Trophozoites’ amoeboid movement also contributes to the lysis of mucosal cells.
Cytolysis.
Cysteine proteinase enzymes are responsible for further tissue lysis
Proteolysis.
(?) by the trophozoites produces discrete ulcers with pinhead center and raised edges. Sometimes, the invasion remains superficial and heals spontaneously.
Mucosal penetration
More often, the trophozoites penetrate to submucosal layer and multiplies rapidly, and spread by lateral and downward extension producing a typical (?) in cross section, with mouth and neck being narrow and base large and rounded.
flask shaped (or tear drop-shaped) ulcer
The (?) are multiple and are confined to the colon, being most numerous in the cecum and next in the sigmoidorectal region.
ulcers
The ulcers generally do not extend deeper than submucosal layer.
Colonic perforation.
Occasionally, the ulcers may involve
the muscular and serous coats of the colon, causing perforation
and peritonitis. This occurs in about 60% of fulminant cases.
Blood vessel erosion may cause hemorrhage.
Colonic perforation.
Occasionally, a granulomatous mass may develop on the intestinal wall.
Amoeboma.
It is the result of cellular responses to a chronic ulcer and often still contains active trophozoites, usually in the cecum or rectosigmoid.
Amoeboma.
It produces wall thickening and or constriction of the lumen, the so-called “napkin ring” lesion and may obstruct the bowel.
Amoeboma.
This may be mistaken for colon cancer
Amoeboma.
Secondary amoebic infection occurs as a result of trophozoites entering portal circulation or by direct extension from the intestinal tissues and becoming lodged in the liver, and other extraintestinal organs such as the lungs, brain, spleen and cutaneous sites.
Extraintestinal amoebiasis
Hepatic involvement is the most common extraintestinal complication of amebiasis.
Hepatic amoebiasis
The dissemination from the primary site in the colon is primarily by the blood stream.
Hepatic amoebiasis
he trophozoites reach the liver through the portal vein.
Hepatic amoebiasis
At times, it may also occur through direct extension from the intestinal ulcer.
Hepatic amoebiasis
It covers both amoebic hepatitis and amoebic liver abscess (ALA).
Hepatic amoebiasis
In ALA, the trophozoites lyze liver cells and forms abscess filled with necrotic debris described as anchovy sauce or chocolate pus.
Hepatic amoebiasis
lt is bacteriologically sterile and free of amoeba.
Hepatic amoebiasis
At the periphery, there is almost normal liver tissue, which contains invading trophozoites.
Hepatic amoebiasis
(?) ranks next to liver abscess in rate of occurrence.
pulmonary amoebiasis
Primary amoebiasis of the lung occurs independently without the presence of hepatic involvement by (?) from the colon wall via the pulmonary circulation into the pulmonary arteries.
direct hematogenous spread
But most often it is secondary to hepatic abscess by direct extension through the diaphragm and therefore, the (?) is the usual area affected. The patient presents with pneumonia with
expectoration of anchovy sauce or chocolate sputum.
lower part of the right lung
Involvement of distant organs is by hematogenous spread and through lymphatics.
Metastatic amoebiasis
Abscesses in kidney, brain, spleen and adrenals have been noticed
Metastatic amoebiasis
Spread to brain leads to severe destruction of brain tissue and is fatal.
Metastatic amoebiasis
This is a result of damaged skin frequently brought in contact with trophozoites.
Cutaneous amoebiasis
It occurs commonly around the perineum or perianal region secondary to amoebic dysentery, also on the skin over the region adjoining the visceral lesion - as in hepatic abscess.
Cutaneous amoebiasis
The prepuce and glans are affected in penile amoebiasis which is acquired through anal intercourse.
Genitourinary amoebiasis
Similar lesions in females may occur on vulva, vagina, or cervix by spread from perineum.
Genitourinary amoebiasis
It is performed for diagnosis of intestinal amoebiasis.
Stool examination
It is not of value in the diagnosis of extraintestinal amoebiasis.
Stool examination
E. histolytica cyst can be detected in stool in less than 15% cases of amoebic hepatitis.
Stool examination
: This is a standard method for routine O & P exam. Trophozoites are primarily recovered from stools that are of soft, liquid, or loose consistency.
Direct fecal smear (DFS)
Formed stool specimens are more likely to contain cysts.
Direct fecal smear (DFS)
Saline mount of fresh unfixed stool demonstrates motile trophozoites, or cysts while iodine preparation primarily demonstrates the cysts only.
Direct fecal smear (DFS)
When patient is suspected of having intestinal amoebiasis, 6 specimens is recommended (however, is rarely requested) and collected on separate days within 14-day period: 3 specimens collected from normal bowel movement and 3 specimens collected after catharsis/purge.
Direct fecal smear (DFS)
Bacteria
Few, Numerous
Pus cells
Scanty, well-preserved; Numerous, degenerated
RBC
Often in rouleaux; Unaltered, scattered
Macrophage
NOT a feature; May be numerous (may have RBC)
Charcot-Leyden crystals
May be present; Absent
Trophozoite
Present; Absent
There are two types of concentration procedures:
flotation and sedimentation
Cysts may be seen and identified, but trophozoites are not likely to be seen. Therefore, this is recommended for isolation and identification of amoebae in non-diarrheic stool.
Stool concentration
It is considered the best practice in the diagnosis of protozoa because it allows examination and recognition of the detailed morphology of the trophozoites or cysts.
Permanent staining
It provides contrasting colors for the parasites and the background. The parasite is examined under high magnification by oil-immersion technique.
Permanent staining
The parasite is examined under high magnification by (?) technique.
oil-immersion
Blue-green, sometimes light pink or with a tinge of purple; Slightly more purple
TRICHROME
Blue-gray; Blue-gray
IRON HEMATOXYLIN
Red, sometimes with a tinge of purple
TRICHROME
Darker than cytoplasm, bluegray to black
IRON HEMATOXYLIN
Green, provides nice contrast with the protozoa
TRICHROME
Lighter shade of blue-gray
IRON HEMATOXYLIN
Scraping obtained by sigmoidoscopy is often contributory.
Examination of sigmoidoscopy specimen
Examination method includes a direct wet mount and permanent staining.
Examination of tissue aspirates/biopsy
Liver abscess material, may be processed and examined in the same manner. Microscopic examination of pus aspirated from liver abscess may demonstrate trophozoite of E. histolytica in less than 20% cases.
Examination of tissue aspirates/biopsy
In case of liver abscess, when diagnostic aspiration is done, the pus obtained from the center of the abscess may not contain amoeba as they are confined to the periphery.
Examination of tissue aspirates/biopsy
The fluid draining after a day or two is more likely to contain the trophozoite. Aspirates from the margins of the abscess would also show the trophozoites.
Examination of tissue aspirates/biopsy
Cysts are never seen in extraintestinal lesions. Trophozoite of E. histolytica may be demonstrated in liver biopsy specimen, in case of hepatic amoebiasis or amoebic hepatitis.
Examination of tissue aspirates/biopsy
It is a more sensitive method in diagnosing chronic and asymptomatic intestinal amoebiasis.
Stool Culture
(?) yields higher positivity for E. histolytica as compared to direct examination.
Culture of stools
Media used for polyxenic culture include:
- Boeck and Drbohlav’s biphasic medium - NIH polygenic medium - Craig’s medium - Nelson’s medium - Robinson’s medium - Balamuth’s medium.
Medium for axenic culture:
- Diamond’s medium
