PARASITOLOGY

Topic: Parasitic Amoebas

Lecture by: Dr. Cabudoy

INTESTINAL AMOEBA Life Cycle

 7 species of amebae occur in humans. These include the following:  The life cycle of E. histolytica consists of two stages:
1. An infective cyst
Pathogenic Commensals
Entamoeba histolytica Entamoeba dispar
Entamoeba moshkovskii
Entamoeba hartmanni
Entamoeba coli
Endolimax nana
Iodamoeba buetschlii
 Entamoeba polecki is an intestinal ameba of pigs and monkeys that
has been occasionally detected in humans, and is a probable cause
of diarrhea 2. An invasive trophozoite form
 Intestinal amoebas are mainly differentiated on the basis of structure
and size
 Trophozoites divide by binary fission
 Most cyst-forming amebae go through nuclear division, and then
divide again after excystation in a new host

PATHOGENIC AMOEBA
Entamoeba histolytica
Taxonomy:
Kingdom: Protista  No host other than humans is implicated in the life cycle, although
Subkingdom: Protozoa natural infection of primates has been reported
Phylum: Sarcomastigophora  The quadrinucleate cyst is resistant to gastric acidity and desiccation,
Subphylum: Sarcodina and can survive in a moist environment for several weeks.
Superclass: Rhizopoda Morphology
Class: Lobosea  Trophozoite
Order: Amoebida o The E. histolytica trophozoites are highly motile and
Family: Entamoebidae possess pseudopodia
Genus: Entamoeba o They vary in size from 12 to 60 µm in diameter (about 20
Species: Entamoeba histolytica µm in average)
o Microscopic examination of fully-passed stool specimens
 The members of this genus are characterized by having a: reveals the characteristic progressive and directional
o Vesicular nucleus movement of trophozoites, with pseudopodia as
o A centrally (or near central) located small karyosome locomotory organelles
o Varying numbers of chromatin granules adhering to the o The hyaline pseudopodium is formed when the clear,
nuclear membrane glasslike ectoplasm, or outer layer is extruded, and the
These nuclear and other morphologic differences granular endoplasm flows into it
distinguish the species of Entamoeba EXCEPT: o Ingested red blood cells are observed as pale, greenish,
1. E. histolytica refractile bodies in the cytoplasm of the ameba
2. E. dispar o Active feeding stage
3. E. moshkovskii (previously known as the Laredo
o Growing stage
strain)
o It has blunt pseudopodia
The three said species are morphologically identical and
o Non-polar cytoplasm
of the same size
o Uninucleated
It was only recently that this E. histolytica species o Nucleus have 5 peripheral chromatin granules with a
complex was resolved. Through isoenzyme analysis central chromosome
polymerase chain reaction (PCR) restriction fragment
length polymorphism (RFLP), and typing with monoclonal
 Cyst
antibodies, these three species are now differentiated.
o Are usually spherical
E. hartmanni, formerly referred to as “small race” of E. o The size may vary from 10 to 20 µm
histolytica, is differentiated primarily on the basis of size o They are characterized by a highly refractile hyaline cyst
wall, 1 to 4 nuclei, and rod-shaped (or cigar-shaped)
Parasite Biology chromatoidal bars
 Entamoeba histolytica is a pseudopod-forming non-flagellated o Dormant resistant stage
protozoan parasite o For immature cysts: bluntly rounded chromatin bars
 It is the most invasive of the Entamoeba parasites (which includes E. o Resistant to acidic environment of the stomach
dispar, E. moshkovskii, E. hartmanni, E. polecki, E. coli, and E. o Undergoes development in the intestines
gingivalis), and the ONLY MEMBER of the family to cause colitis and
o It can be Uninucleated, Binucleated  immature
liver abscess
o If Quadrinucleated  mature
o Has amoeboid movement
o Susceptible to heat about 40oC
o Can be viable in moist environment for about 1 month

Page 1 of 8
 PARASITOLOGY
Topic: Parasitic Amoebas
Lecture by: Dr. Cabudoy

Lecture Discussion: Trophozoites vs. Cysts Lecture Discussion: Life Cycle of Entamoeba histolytica
EXCYSTATION happens in the small intestines. It is the transformation of the
CYSTS into TROPHOZOITES
Why is there a need to become trophozoites? It’s because CYSTS cannot
cause disease. It is the TROPHOZOITES that can cause the manifestation
of disease  the trophozoite is the pathogenic stage

Once the cysts become trophozoites, it will go to the large intestine. The
trophozoites are toxic to the tissues of the colon causing ulcers  leads to
amebiasis

Amebiasis is a term referring to Entamoeba histolytica. This means that

if a person has an infection of Entamoeba coli, Iodamoeba buetschlii,
Endolimax nana, or Entamoeba hartmanni  It is NOT amebiasis
Amebiasis  presents with symptoms (which is only caused by E.
histolytica)

Some trophozoites will enter the ulcer, some will stay in the large intestine
to destroy more tissue, some will go into the blood vessels underneath the
submucosa  going to the blood stream, and some will go ENCYSTATION
Trophozoite  Encystation  from TROPHOZOITES turning into CYSTS
 With prominent pseudopods (mobile form)  used for  Cysts is more RESISTANT to the environment when it goes out in
locomotion the feces  survives better then trophozoites
 It is non-flagellated o If the trophozoites are the one that goes out in the
 Uninucleated feces  it gets easily killed by the environment
 Remember that the job of the CYSTS is to INFECT while the job of
Cyst the TROPHOZOITES is to INVADE & DESTROY tissues
 Can have 1-4 nuclei
o 1 or 2 nuclei  immature cyst The cysts will then later on find another host to infect by surviving an
o 4 nuclei  mature cyst environment (usually through water)
 What is the importance of knowing whether if the cyst is mature
or immature? We will be able to know whether the cyst is Other Information about Entamoeba histolytica
INFECTIVE or not. It is the MATURE cyst (having 4 nuclei) that is  E. histolytica is a eukaryotic organism but has several unusual
infective features, including the lack of organelles that morphologically
resemble mitochondria
Modes of Transmission  Because nuclear-encoded mitochondrial genes such as pyridine
 Infection with E. histolytica occurs when CYSTS are ingested from nucleotide transhydrogenase and hsp60 are present, E. histolytica,
fecally-contaminated material at one time may have contained mitochondria
 Other modes of transmission include venereal transmission through:  There is no rough endoplasmic reticulum or Golgi apparatus,
o Fecal-oral contact although cell surface and secreted proteins contain signal sequences,
o Direct colonic inoculation through contaminated enema and tunicamycin inhibits protein glycosylation
equipment  Ribosomes form aggregated crystalline arrays in the cytoplasm of the
trophozoite
1. Cysts and trophozoites are  Some differences in biochemical pathways from higher eukaryotes
passed in feces include:
2. Cysts are typically found in o Lack of glutathione metabolism
formed stool, whereas o Use of pyrophosphate instead of ATP at several steps in
trophozoites are typically glycolysis
found in diarrheal stool. o Inability to synthesize purine nucleotides de novo
Infeciton by E. histolytica
 Glucose is actively transported into the cytoplasm, where the end
occurs by ingestion of
products of carbohydrate metabolism are:
mature cysts in fecally
o Ethanol
contaminated food, water,
o Carbon dioxide
or hands
o Acetate (formed under aerobic conditions)
3. Excystation occurs in the
small intestine
Trophozoites have the ability to colonize and/or invade the large bowel,
4. Trophozoites are released,
while cysts are never found within invaded tissues
which migrate to the large
E. histolytica trophozoites multiply by binary fission. They encyst producing
intestine
uninucleate cysts, which then undergo two successive nuclear divisions to
5. The trophozoites multiply
form the characteristic quadrinucleate cysts
by binary fission and
produce cysts
Both stages are passed in the feces (going back to 1)

Page 2 of 8
 PARASITOLOGY
Topic: Parasitic Amoebas
Lecture by: Dr. Cabudoy

Pathogenesis  Ameboma
 The proposed mechanisms for virulence are: o Occurs in less than 1% of intestinal infections
1. Production of enzymes or other cytotoxic substances o It clinically presents as a mass-like lesion with abdominal
2. Contact-dependent cell killing pain and a history of dysentery
3. Cytophagocytosis o It can be mistaken for carcinoma
 In vitro, amebic killing of target cultivated mammalian cells involve: o Asymptomatic ameboma may also occur
1. Receptor-mediated adherence of ameba to target cells
2. Amebic cytolysis of target cells  Amebic liver abscess (ALA)
3. Amebic phagocytosis of killed or viable target cells o It is the most common extra-intestinal form of amebiasis
o The cardinal manifestations of ALA are:
 E. histolytica trophozoites adhere to the colonic mucosa through a
 Fever
galactose-inhibitable adherence lectin (Gal lectin). Then, the amebae
 Right upper quadrant (RUQ) pain
kill mucosal cells by activation of their caspase-3, leading to their
apoptotic death engulfment Several studies have shown these two as the most
 Recent studies have shown that susceptibility of humans to E. frequent complaints, particularly in acute cases (<2
histolytica infection is associated with specific alleles of the HLA weeks duration)
complex In a Philippine study involving 206 patients with
 Majority of cases present as asymptomatic infections with cysts probable ALA as diagnosed by ultrasound, the two
being passed out in the stools (cyst carrier state) most frequent manifestations were fever in 77% and
 The recent differentiation of E. dispar and E. histolytica by PCR has RUQ pain in 83%
confirmed the high prevalence of non-pathogenic E. dispar compared
to the pathogenic E. histolytica. However, studies also revealed that Chronic disease (>2 weeks duration) is found in older
most E. histolytica infections in endemic communities are patients and it involves wasting with significant weight
asymptomatic loss rather than fever. Only 30% of ALA cases have
concurrent diarrhea. However, daily stool cultures
revealed that 72% harbored trophozoites even in
Additional Information:
asymptomatic infections. Mortality in uncomplicated
 E. histolytica has surface enzmes capable of digesting epithelial cells
ALA is less than 1%
and hydrolysis of the host tissue
 E. histolytica causes flask-shaped ulcers to develop in the large o ALA may have all acute presentation of <2 weeks duration
intestine or a chronic one of >2 weeks duration
 It can also cause Amebic Liver Disease (ALA) by travelling through the o In ALA, the most serious complications are:
hepatic portal vein 1. Rupture into the pericardium with a mortality
 It can also migrate to the lungs and brain. It can cause Hepatic, rate of 70%
Pulmonary or Cerebral Amebiases 2. Rupture into the pleura with mortality of 15 to
 External ulcers cause by E. histolytica such as Ocular amebiasis and 30%
Genital amebiasis do not heal by themselves 3. Super infection
o Intraperitoneal rupture, which occurs in 2-7.5% of cases,
Lecture Discussion: Pathogenesis is the second most common complication
Trophozoites  are not only cytotoxic but also cytolytic, because upon However, it is NOT as serious as colonic perforation
contact with the epithelial cells of the mucosa of the colon, it can kill the cell because ALA is sterile
(columnar cells). Its proteinases can lyse the cells  leads to necrosis 
ulcer. Aside from this, patient can also be anemic due to the capability of the  Secondary amebic meningoencephalitis occurs in 1-2%, and it
trophozoites to cytophagocytose red cells should be considered in cases of amebiasis with abnormal mental
status
Clinical Manifestations  Renal involvement caused by extension of ALA or retroperitoneal
 Amebic colitis clinically presents as: colonic perforation is RARE
o Gradual onset of abdominal pain and diarrhea with or  Genital involvement is caused by fistulae from ALA and colitis or
without blood and mucus in the stools primary infection through sexual transmission
o Fever is not common and it occurs only in one third of
patients  Natural or innate immunity to E. histolytica in the intestines involves
o Although some patients may only have intermittent mucin inhibition of amebic attachment to the underlying mucosal
diarrhea alternating with constipation, children may cells
develop fulminant colitis with severe bloody diarrhea, In the systemic circulation, the mechanism is that of complement-
fever, and abdominal pain mediated killing of trophozoites
o The onset of amebic colitis may be sudden after an
incubation period of 8 to 10 days, or after a long period  Acquired immunity primarily involves cell-mediated responses,
of asymptomatic cyst carrier state although humoral responses may also contribute to anti-amebic
o The most serious complication of amebic colitis is: immunity
1. Perforation  Activated T-cells kill E. histolytica by:
2. Secondary bacterial peritonitis a) directly lysing trophozoites in a contact-dependent
Colonic perforation occurs in 60% of fulminant process
colitis cases b) producing cytokines which activate macrophages and
other effector cells (neutrophils and eosinophils)
c) providing helper effect for B-cell antibody production

Page 3 of 8
 PARASITOLOGY
Topic: Parasitic Amoebas
Lecture by: Dr. Cabudoy

Clinical Manifestation continued…..  Another differential is inflammatory bowel disease. Amebic colitis
Additional Information: From Belizario & de Leon should be ruled out before steroid therapy for inflammatory bowel
In vitro studies using activated murine and human T-cells disease is started because of the risk of developing toxic megacolon
demonstrated significant killing of trophozoites in a contact-  The differential diagnoses of ALA include:
dependent and antibody independent manner o Pyogenic liver abscess
Cytokine studies revealed that interferon (IFN) and interleukin (IL- o Tuberculosis of the liver
2) may have a role in activating macrophages for amebicidal o Hepatic carcinoma
activity  On the other hand, genital amebiasis should be differentiated from:
More recent studies demonstrated that activated macrophages o Carcinoma
produce nitric oxide (NO) which was lethal to trophozoites. o Tuberculosis
Tumor necrosis factor (TNF) was shown to stimulate NO o Chancroid
production. Although it is known that antibodies are produced o Lymphogranuloma venereum
against amebic antigens, there has been no direct evidence of T-
cell help for B-cells Lecture Discussion: Clinical Manifestations

Studies have revealed that the principal antibody-dependent cell Amebic dysentery  this is an acute disease characterized by bloody
cytotoxicity (ADCC) did not work against amebae diarrhea and abdominal cramping. Most patients with amebiasis presents
this
Antibodies which were detected by seroepidemiologic studies
and secretory IgA isolated in the gut may merely be an indicator Viral diarrhea vs. Dysentery (Bloody diarrhea)
of current or recent invasive amebiasis Viral diarrhea Bloody diarrhea
Stool is watery Stool color is black
With abdominal cramping
 Amebic modulation of host immune responses exists
No abdominal cramping (secondary to destruction of the tissues
For instance, infected human subjects and animals have been of the colon)
shown to be in a state of immunosuppression during the acute
stage of amebiasis. This state, characterized by:
How would we be able to know if an ulcer is secondary to E. histolytica?
o T-cell hyporesponsiveness
Look for the presence of trophozoites. Since it can do cytophagocytosis 
o Suppressed proliferation
o Cytokine production there will be presence of red blood cells
o Depressed delayed-type hypersensitivity (DTH)
o Macrophage suppression

This is favorable for amebic survival. It is the reversal of these

modulatory effects, which is the key in controlling amebiasis

Differential Diagnosis
 Acute amebic colitis should be differentiated from bacillary
dysentery of the following etiology:
o Shigella, Salmonella, Campylobacter, Yersinia and
enteroinvasive Escherichia coli
Although stools may be grossly bloody or heme-positive in both
conditions, fever and significantly elevated leukocyte count are
LESS COMMON in amebic colitis

Comparison of Bacillary & Amebic dysentery

Bacillary Dysentery Amebic Dysentery
May be epidemic Seldom epidemic
Acute onset Gradual onset
Prodromal fever and malaise Amebic Liver Abscess (ALA)  happens when there is an ulcer, the
No prodromal features trophoziotes can go into the blood vessels  goes to the bloodstream 
common
Vomiting common No vomiting then it goes into the portal circulation (via hepatic portal vein)  it gets
Patient prostrate Patient usually ambulant trapped in the liver  the liver will get destroyed due to its virulence 
Watery, bloody diarrhea Bloody diarrhea abscess formation
Odorless stool Fishy odor stool o Symptoms: RUQ pain
Stool microscopy: High grade fever
Stool microscopy:
Few bacilli, red cells, Why is it Right Upper Quadrant? It’s because the right lobe of
Numerous bacilli, pus cells,
trophozoites with ingested red the liver is the most common area of abscess formation
macrophages, red cells, no
blood cells, Charcot-Leyden
Charcot-Leyden crystals
crystals How would we know if this liver abscess is NOT due to other
Abdominal cramps common and organisms? Aspiration of the abscess  smear & microscopy
Mild abdominal cramps
severe  look for the presence of trophozoites
Tenesmus common Tenesmus uncommon
Natural history: Why do we need to aspirate the abscess? If we do not aspirate
Natural history:
Lasts for weeks, dysentery the abscess, that abscess itself can be a good culture for group
Spontaneous recovery in a few
returns after remission;
days, weeks or more; no relapse of other organisms
infection persists for years

Page 4 of 8
 PARASITOLOGY
Topic: Parasitic Amoebas
Lecture by: Dr. Cabudoy

Lecture discussion on Clinical Manifestations continued…..  Concentration methods such as Formalin Ether/Ethyl Acetate
The liver is not the only organ affected by E. histolytica. It can also go to the Concentration Test (FECT) and Merthiolate Iodine Formalin
lungs and brain Concentration Test (MIFC) are more sensitive than the DFS for
detection of cysts
Signs & Symptoms  The following morphologic structures are noted:
of Amebiasis: Fever o size of the cyst
Abdominal pain o number of nuclei
Bloody diarrhea o location and appearance of the karyosome
o the characteristic appearance of chromatoid bodies
Fever  happens because trophozoites attract
o presence of cytoplasmic structures such as glycogen
cytokines (chemoattractant) and neutrophils. The
WBCs also release substances that can cause fever vacuole
E. histolytica can, thus, be differentiated from the non-pathogenic
species, E. hartmanni, E. coli, E. nana, and Iodameba büetschlii
Amebic colitis  there is flask-shaped ulcer

 Stool culture using Robinson’s and Inoki medium is more sensitive

Epidemiology
than stool microscopy, but is not routinely available
 More common in tropical and subtropical countries
 Differentiation between E. histolytica and E. dispar is not possible by
 Prevalence  1-5% worldwide
microscopy. This can only be done by:
 There are 50 million E. histolytica infection cases worldwide
o PCR
 40,000 to 100,000 deaths due to amebiasis in the world per year
o Enzyme-linked immunosorbent assay (ELISA)
 Amebiasis is the 3rd most important parasitic disease, after malaria o Isoenzyme analysis  primarily a research technique
and schistosomiasis
 It is 2nd to malaria as the top cause of mortality among parasitic  Detection of antibodies in the serum (Serologic Testing) is still the
protozoans key in the diagnosis of ALA
 Humans are the major reservoirs of infection with E. histolytica It must be noted that in ALA, microscopic detection cannot be
 Ingestion of food and drink contaminated with E. histolytica cysts done because aspiration is an invasive procedure, and
from human feces, and direct fecal-oral contact are the most trophozoites are missed because they are located in the periphery
common means of infection of the abscess
Amebic infection is prevalent in the Indian subcontinent, Africa,
East Asia, and South & Central America
 To date, serological tests for amebic disease include:
o Indirect hemagglutination (IHAT)
 In developing countries, prevalence depends on the level of
o Counter immunoelectrophoresis (CIE)
sanitation, crowding, socio-economic status, cultural habits, and age
o Agar gel diffusion (AGD)
 In developed countries, infection is usually caused by E. dispar, and
o Indirect fluorescent antibody test (IFAT)
is prevalent in certain groups:
o ELISA
o Immigrants
o Travelers from endemic countries The IHAT can detect antibodies of a past infection even as
o Homosexual males (men having sex with men) long as 10 years ago
o HIV patients In contrast, the antibodies detected by ELISA, AGD, and CIE
o Institutionalized people are of short duration, lasting for a few months
Antibodies have been demonstrated in asymptomatic
Diagnosis intestinal infections so that serology can be used in the
 The standard method of parasitologic diagnosis is microscopic monitoring of a cyst carrier
detection of the trophozoites and cysts in stool specimens
o Ideally, a minimum of three stool specimens collected on
different days should be examined  Ultrasound, computerized tomography (CT scan), and magnetic
o For detection of trophozoites, fresh stool specimens resonance imaging (MRI)  non-invasive and sensitive methods in
should be examined within 30 minutes from defecation early detection of ALA
o Using the direct fecal smear (DFS) with saline solution Ultrasound typically shows a round or oval hypoechoic area with
alone, the microscopist can observe trophozoite motility wall echoes
Unidirectional movement is characteristic of E.
histolytica

o Using saline and methylene blue, Entamoeba species will

stain blue, thus, differentiating them from white blood
cells
o Using saline and iodine, the nucleus and karyosome can
be observed to differentiate E. histolytica from the non-
pathogenic amebae (E. hartmanni, E. coli, Endolimax
nana)
o The detection of E. histolytica trophozoites with In 80% of cases, this finding is seen in the right lobe of the liver.
ingested red blood cells is diagnostic of amebiasis. Multiple lesions occur in 50% of acute cases, and aspiration may
Charcot-Leyden crystals can also be seen in the be required to differentiate amebic from pyogenic abscess
stool

Page 5 of 8
 PARASITOLOGY
Topic: Parasitic Amoebas
Lecture by: Dr. Cabudoy

Lecture Discussion: Diagnosis  Vaccines can be a cost-effective and potent strategy for amebiasis
prevention and eradication
Specimens used in the diagnosis of Entamoeba histolytica: Unlike in other protozoan infections, amebic vaccine
1. Stool development has fewer problems. The ameba life cycle is simple,
2. Blood and no intermediate hosts are involved
Amebae are extracellularly located, and do not undergo
Since patients with amebiasis, most of the time, presents with diarrhea  antigenic variation. All these characteristics are supportive of an
the #1 sample is stool. This is examined for the presence of parasite achievable amebic vaccine
(trophozoites)
For asymptomatic patients  what is seen are cysts COMMENSAL or NON-PATHOGENIC AMOEBAS
Parasite Biology
Serologic testing is most commonly used in the diagnosis of ALA. Why?  Commensal amebae must be differentiated from pathogenic E.
Because patients with ALA do not have amoebas in the intestines. It is already histolytica to avoid unnecessary treatment of patients infected with
in the liver. Serologic testing  sample of blood is examined for the presence non-pathogenic species
of antibody-antigen reaction from E. histolytica
The three genera of intestinal amebae can be differentiated through the
If upon microscopic examination you see that the CYST has more than 4 morphological features of their nuclei:
nuclei, then it is NOT E. histolytica. It is already Entamoeba coli  The genus Entamoeba has a spherical nucleus with a distinct nuclear
o Entamoeba coli chromatoidal body has sharp and splintered ends membrane lined with chromatin granules and a small karyosome
o Entamoeba histolytica chromatoidal body has rounded end found near the center of the nucleus
 Trophozoites usually have only one nucleus
Treatment and Prognosis
 The treatment of amebiasis has two objectives:  The genus Endolimax has a vesicular nucleus with a relatively large,
a) To cure invasive disease at both intestinal and irregularly-shaped karyosome anchored to the nucleus by
extraintestinal sites achromatic fibrils
b) To eliminate the passage of cysts from the intestinal
lumen  The genus Iodamoeba is characterized by a large, chromatin-rich
 Metronidazole is the drug of choice for the treatment of invasive karyosome surrounded by a layer of achromatic globules and
amebiasis (kills the trophozoites) anchored to the nuclear membrane by achromatic fibrils
o Other 5-nitroimidazole derivatives such as tinidazole and
secnidazole are also effective
 Diloxanide furoate is the drug of choice for asymptomatic cyst
passers
o It is also given after a course of metronidazole for invasive
amebiasis

 Percutaneous drainage of liver abscess is indicated for patients who

do not respond to metronidazole and who need prompt symptomatic
relief of severe pain
It is also done for those who have left lobe abscess that may
rupture into the pericardium, large abscesses in danger of rupture,
and multiple abscesses with a probable associated pyogenic
etiology

Prevention and Control

 The prevention and control of amebiasis depends on integrated and
community-based efforts to improve environmental sanitation, and
to provide for sanitary disposal of human feces, safe drinking water,
and safe food
 These efforts become more sustainable through health education
and promotion
 The proper use of latrines and practice of proper hygiene, such as
washing of hands, should be emphasized
 In communities where potable water is not available, drinking water
should be boiled or filtered
 Vegetables and fruits which are eaten raw should be thoroughly
washed
 The use of night soil for fertilizer should be avoided
 Prompt diagnosis and treatment of amebiasis cases should be done
 Food handlers should be screened for cyst carriage, and
asymptomatic cyst carriers should be treated

Page 6 of 8
 PARASITOLOGY
Topic: Parasitic Amoebas
Lecture by: Dr. Cabudoy

Parasite Biology continued….. Entamoeba moshkovskii

 Entamoeba moshkovskii isolates, although first detected in sewage,
have been reported in some areas, such as North America, Italy,
South Africa, Bangladesh, India, Iran, and Australia
 It is a non-pathogenic species that is morphologically
indistinguishable from E. histolytica and E. dispar, but differs from
them biochemically and genetically
 It is also physiologically unique—it being osmotolerant, able to grow
at room temperature (25-30°C optimum), able to survive at
temperatures ranging from 0 to 41°C
 All human isolates have been found to belong to one group
“ribodeme 2”

Entamoeba hartmanni
 The appearance of E. hartmanni is relatively similar to that of E.
histolytica apart from its smaller size
 Its trophozoites of the measure from 3 to 12 µm in diameter
 Mature cysts measure 4 to 10 µm, are quadrinucleated like E.
histolytica, and have rod-shaped chromatoid material with rounded
or squared ends
 Unlike E. histolytica, E. hartmanni does not ingest red blood cells

 All species have the following stages: Entamoeba coli

o Trophozoite
 Entamoeba coli is cosmopolitan in distribution, and is considerably
o Precyst
more common than other human amebae
o Cyst
 Trophozoites of E. coli measure 15 to 50 µm in diameter
o Metacystic trophozoite
 It can be differentiated from E. histolytica trophozoite by the
EXCEPTION: following features:
Entamoeba gingivalis, which has no cyst stage, and does 1. A more vacuolated or granular endoplasm with bacteria
not inhabit the intestines and debris, but no red blood cells
2. A narrower, less-differentiated ectoplasm
 Humans are infected by commensal intestinal amebae through 3. Broader and blunter pseudopodia used more for feeding
ingestion of viable cysts in food or water than locomotion
4. More sluggish, undirected movements
 Cysts pass through the acidic stomach and remain viable because of
5. Thicker, irregular peripheral chromatin with a large,
protective cyst walls
eccentric karyosome in the nucleus
 Excystation occurs in the alkaline environment of the lower small
 An E. coli cyst may be differentiated from E. histolytica by:
intestines
1. Its larger size (10 to 35 µm in diameter)
 Metacystic trophozoites colonize the large intestines and live on the
2. More nuclei (eight vs. four in E. histolytica)
mucus coat covering the intestinal mucosa
3. More granular cytoplasm,
 These amebae are non-invasive and do not cause disease
4. Splinter-like chromatoidal bodies
 Reproduction is by binary fission of the trophozoites
 Iodine staining reveals dark-staining, perinuclear masses, which are
 Encystation occurs as amebae pass through the lower colon where
actually glycogen
colonic contents are more dehydrated
 Its location, surrounding the nucleus, is more characteristic of E. coli
Entamoeba dispar compared to E. histolytica
 Entamoeba dispar is morphologically similar to E. histolytica, but
their DNA and ribosomal RNA are different and does not invade the
tissue
 Indistinguishable by microscopy
 It can be differentiated by PCR, ELISA, and isoenzyme analysis

Page 7 of 8
 PARASITOLOGY
Topic: Parasitic Amoebas
Lecture by: Dr. Cabudoy

Entamoeba polecki Iodamoeba buetschlii

 Entamoeba polecki is a parasite found in the intestines of pigs and  The trophozoite averages 9 to 14 µm in diameter (ranging from 4-20
monkeys µm)
 Like E. coli, motility of trophozoites of E. polecki is sluggish  It is identified by its characteristic large, vesicular nucleus with a
 A small karyosome is centrally located in the nucleus large, central karyosome, surrounded by achromatic granules
 E. polecki can be distinguished from E. histolytica in that the former’s There are no peripheral chromatin granules on the nuclear
cyst is: membrane
o Consistently uninucleated
o Chromatoidal bars are frequently angular or pointed  The cyst is about 9 to 10 µm in diameter (ranging from 6-16 µm), is
 In stained fecal smears, the nuclear membrane and karyosome are uninucleated, and has a large glycogen body which stains dark brown
very prominent with iodine

Entamoeba chattoni
 Entamoeba chattoni, which is found in apes and monkeys, is Diagnosis
morphologically identical to E. polecki  Diagnosis is done through stool examination
 More recently, it has been detected in eight human infections  Formalin ether/ethyl acetate concentration technique (FECT) and
 Identification of E. chattoni was done via isoenzyme analysis iodine stain are useful to differentiate the species
 For E. gingivalis, a swab between the gums and teeth is examined for
Entamoeba gingivalis trophozoites
 Entamoeba gingivalis can be found in the mouth  Cysts are recovered from formed stools
 The trophozoite measures 10 to 20 µm  Trophozoites are recovered from watery or semi-formed stools
 It moves quickly, and has numerous blunt pseudopodia  Trophozoites are best demonstrated by direct fecal smear
 Food vacuoles that contain cellular debris (mostly leukocytes, which  In recovering cysts, the use of concentration techniques like FECT and
is characteristic of this species) and bacteria are numerous zinc sulfate flotation is useful
 E. gingivalis lives on the surface of gum and teeth, in gum pockets,
Treatment
and sometimes in the tonsillar crypts
 No treatment is necessary because these amebae do not cause
 They are abundant in cases of oral disease
disease
 This species has no cyst stage
 Transmission is most probably direct:
o through kissing
o droplet spray References:
o by sharing utensils  Medical Parasitology in the Philippines by
Belizario & de Leon (3rd Ed.)
Endolimax nana  Lecture Notes
 Endolimax nana occurs with the same frequency as Entamoeba coli
 Trophozoites are small, with a diameter of 5 to 12 µm, and exhibit
sluggish movement
 They have blunt, hyaline pseudopodia
 The nucleus has a large, irregular karyosome
 Food vacuoles found in the cytoplasm may contain bacteria
 Cysts measure about the same size as trophozoites, and are
quadrinucleated when mature

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