Biology of parasitic protozoa
VI. Amoebae: Heterolobosea (Excavata), Amoebozoa (Amoebozoa)
Andrea Bardůnek Valigurová
andreav@sci.muni.cz
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Amoebae
• organisms which free-living alter its shape, primarily by extending and
retracting pseudopodia
• pseudopodia extend and contract by the reversible assembly of actin
monomers into microfilaments
• lobopodia, filopodia, reticulopodia, axopodia
• in older classification most amoebae were placed in the class/subphylum
Sarcodina
• not a single taxonomic group = supergroups comprising amoebae: Excavata,
Amoebozoa, SAR
• mostly free-living species - some are predatory and consume bacteria, others
are detritivores and feed on dead organic material
• amoebae typically ingest the food by phagocytosis
5 supergroups = megagroups
Pseudopodia (pseudopods) in Amoebae
Amoebozoa
(Amoebozoa)
Heterolobosea
(Excavata)
Rhizaria
(SAR)
lobopodia
filopodia
axopodia
reticulopodia
Phagocytosis in Amoebae
5 supergroups = megagroups
Excavata
• have a conspicuous ventral feeding groove that is “excavated” from one side,
and through which pass one or more recurrent flagella; the ventral groove has
characteristic ultrastructure and is supported by microtubules
• variety of free-living and symbiotic forms
• not a monophyletic group
• paraphyletic group with the ancestors of other living eukaryotes
• parasitic species in Discoba•: Heterolobosea•••
• Heterolobosea have lost some of Excavata structures
Heterolobosea
• about 140 described species
• amoebae with eruptive pseudopodia, alternating with flagellated phase flagellated
cells usually with 2 or 4 flagella
• amoeboid, flagellate and resting stage (cyst) = amoeboflagellates
• one or two stages are unknown and presumably have been reduced in many taxa
• remains unclear whether Heterolobosea represent sexual or asexual organisms
• representatives capable of feeding usually use a groove like cytostome
• flattened, often discoidal mitochondrial cristae
• most important heterolobosean taxon is the genus Naegleria comprising human
parasite Naegleria fowleri and model organism N. gruberi
amoebae
flagella permanently flagella temporarily no flagella
Percolomonas
flagellates
Psalteriomonas
amoeboflagellates
Vahlkampfia
Naegleria
Heterolobosea
Heterolobosea - amphizoic amoebae
• also called amphizoic amoebae for their ability to exist as free-living organisms
and only occasionally invade the host and live as parasites in its tissue
• important human pathogen: Naegleria fowleri
genus Naegleria
• about 300 cases of human primary amoebic meningoencephalitis (PAM), while
only 5 PAM patients survived
Life cycle of Naegleria gruberi
Schematic view of Naegleria amoeba and flagellate forms
Life cycle in Heterolobosea
https://www.youtube.com/watch?v=uibyrT3oQL8
• thermophilic free-living amoeba
• surface of vegetation and mud
• pear shaped motile stage with 2 flagella - in surface water
(usually not found in CSF)
• slug shaped amoebic trophozoite (10-25 μm) with rounded
pseudopodia (lobopodia) - infective for humans and observed in
CSF and brain tissue
• uninucleated cysts found on the surface of vegetation and in mud
Naegleria fowleri
Heterolobosea
Life cycle of Naegleria fowleri
https://www.youtube.com/watch?v=Thp5O-i7Sgc
https://www.youtube.com/watch?v=zFEXdnUbTZE
Naegleria fowleri
• water containing N. fowleri
amoeba stage inhaled
through the nose
• enters the nasal and olfactory
nerve tissue, travelling to the
brain - bulbus olfactorius
https://www.youtube.com/watch?v=7OPg-ksxZ4Y
• acute, fulminating haemorrhagic
meningoencephalitis in healthy children
and young adults - primary amoebic
meningoencephalitis (PAM)
• worldwide distribution in fresh and warm
water (lakes, streams, spas, heated but
unchlorinated swimming pools, hot springs,
hydrotherapy and remedial pools, aquaria,
sewage,…)
• thermophilic, tolerates temperatures of up
to 45 °C (optimum 37 °C)
• abundant during summer
• reduction of osmotic pressure  formation
of flagellar stages
Naegleria fowleri
• amoebae enter the CNS following attachment to the
olfactory nerve and migrate to the olfactory bulb
(bulbus olfactorius) of the forebrain, invading the
brain  widespread infections, haemorrhages and
necrosis
Course and clinical symptoms of naegleriasis
• rapid onset of symptoms in 3-5 days after the exposure
• stage 1: severe frontal headache, fever, nausea, vomiting
• stage 2: stiff neck, seizures, altered mental, status, hallucinations, coma
• death in 1-18 days (median 5 days) after symptoms begin
• signs and symptoms of N. fowleri infection are similar to bacterial meningitis, which
lowers the chances of diagnosing PAM at first
• the outlook for patients is poor; early diagnosis and new treatments can increase their
chances for survival
Pathology of PAM
A section of the cerebral portion of the brain from a PAM patient showing
large clusters of N. fowleri trophozoites and the destruction of the normal
brain tissue architecture. Inset: Higher magnification of N. fowleri trophozoites
(arrows). HE.
Extensive haemorrhage and necrosis is present in the brain, mainly
in the frontal cortex.
Focal haemorrhage and necrosis in frontal cortex.
Pathology of PAM
Naegleria fowleri-associated disease in cattle. A) Brain positioned upside-down. Left olfactory bulb shows marked enlargement
and irregular surface. B) Cross-sectioned brain, Thalamus shows a focally extensive and poorly demarcated area of necrosis. C-D)
Histological sections of brain. Blood vessels show marked fibrinoid necrosis of their wall and thrombosis. Rarefaction of adjacent
neuropil (detail in D) with multiple N. fowleri trophozoites (arrows).
Pathogenesis of Naegleria fowleri
• forms sucker like appendages or amoebostomes
• nibbles away at the cells and tissues (trogocytosis)
• contact-dependent cytolysis of brain tissue by the amoeba
• secretion of cytolytic factors causing destruction of cell membrane, including a poreforming
protein similar to perforin
Diagnosis and treatment of naegleriasis
Microscopy
✓ wet mount examination of the CSF
(actively moving amoebae)
✓ Giemsa or trichrome stained CSF
smears
Cultivation
✓ at 37 °C on agar with killed bacteria
(Enterobacter, Escherichia)
Histology (trichrome staining)
✓ amoebae with typical nuclear
morphology
✓ located mostly perivascularly
Treatment
• only 5 PAM patients survived (permanent brain damage)
• amphotericin B i.v. + intrathecally
• rifampin p.o. + miconazol i.v. + intrathecally
Epidemy of PAM in Czech Republic
• 18 cases of PAM in Czechia
• 1962-1965: 16 cases (biggest PAM epidemy)
• 8-25 years old patients
• swimming pool Ústí nad Labem:
VIII.1962: 3 cases
VII. 1963: 6 cases
XI. 1964: 5 cases
IX. 1965: 2 cases
• 1968: 1 case: swimming poll in Most
• 1984: 1 case: stream with cooling water from
power station
Prevention of Naegleria fowleri infection
Prevention of Naegleria fowleri infection
Naegleria australiensis
• pathogenic to laboratory mice
Naegleria gruberi
• non-pathogenic, free-living amoeba
Heterolobosea
5 supergroups = megagroups
Amoebozoa
• taxonomic group containing about 2,400 described species of amoeboid protozoa
• monophyletic supergroup
• blunt, finger-like, lobose pseudopodia
• phagocytosis as a primary mode of nutrition
• if present mitochondria with tubular cristae; many species secondarily lost
mitochondria
• majority lack flagella
• some of them also called „amphizoic amoebae“
• two basic groups:
▪ Lobosa - non flagellated amoebae with blunt, lobose pseudopodia
▪ Conosa - both amoeboid and flagellated cells, characteristically with
more pointed or slightly branching pseudopodia
Smirnov et al. (2011): Prostist 162
https://doi.org/10.1016/j.protis.2011.04.004
Lobosa: Acanthamoebidae - amphizoic amoebae
• invade a host and live as parasites within host tissue
• important pathogens:
▪ Acanthamoeba spp. - about 130 cases of human granulomatous amebic
encephalitis (GAE) , more than 3000 cases of human amoebic keratitis (AK)
▪ Balamuthia mandrillaris - more than 100 cases of GAE
▪ Sappinia diploidea - 1 or more cases (?) of human amoebic encephalitis (AE)
Amoebozoa - amphizoic amoebae
genus Acanthamoeba
• thorn-like pseudopodial projections = acanthopodia
(„acanthus“ = spiny, thorny)
• trophozoites (15-30 μm) with slow movement, no
flagellate stages
• cosmopolitan, ubiquitous occurrence in soil and water (fresh, brackish, and sea water) commonly
found in lakes, swimming pools, tap water, heating and air conditioning units,
sewage, contact lens equipment
• can be also found in dental treatment units; dialysis machines; mammalian cell lines;
vegetables; human nostrils and throats; human and animal brain, skin, lung tissues
• more than 24 species  13 human species: Acanthamoeba culbertsoni, A. castelanii,
A. astronyxis, A. hatchetti, A. rhysodes, A. palestinensis, A. polyphaga, …
• 3 morphological groups based on size and character of trophozoites and cysts
• often harbouring pathogenic bacteria
• cyst with double-layered wall - outer wrinkled ectocyst and inner
endocyst (stellate, polygonal, oval or round), large nucleus with a
central dense nucleolus
https://www.youtube.com/watch?v=pi2bElfM7hA
https://www.youtube.com/watch?v=qBIdfJEJMK0
Life cycle of Acanthamoeba spp.
Trophozoites
Life stages of Acanthamoeba spp.
https://www.youtube.com/watch?v=08HqkXNNj_g&t=6s
https://doi.org/10.1038/s41598-019-41084-6Cysts
https://www.youtube.com/watch?v=yH4OrA7meio
Life stages of Acanthamoeba spp.
Active phagocytosis via amebostomes („food cups“)
SEM of trophozoites illustrating the presence of surface structures termed food cups. A) Food cups present on the surface
of a trophozoite of Acanthamoeba culbertsoni are temporary structures that form and reform for the intake of bacteria, yeast, or
cellular debris. B) Food cup present on the surface of A. astronyxis trophozoite used to ingest bacteria. C) Food cup present on
the surface of an A. castellanii trophozoite in the apparent process of ingesting a cultured nerve cell. D) Higher magnification of
trophozoite in C showing the food cup during putative ingestion. https://doi.org/10.1128/CMR.16.2.273-307.2003
The figure describes how Acanthamoeba and bacteria interact, which may lead to the amoebae acting as
predator, Trojan horse or reservoir. Left: Acanthamoeba in a bacteria-rich environment following which selected
bacteria are taken up by the amoeba. Middle section: Two main options following intake of bacteria are depicted,
namely, digestion or survival of the bacteria. Right: Bacteria surviving internalisation into Acanthamoeba, namely, using
the amoeba as a transmission vehicle or replication site. https://doi.org/10.1007/s12223-021-00889-7
Interaction of Acanthamoeba with bacteria
• Acanthamoeba can be spread to the eyes through contact lens use, cuts, or skin
wounds or by being inhaled into the lungs
• most people are exposed to Acanthamoeba during their lifetime, but very few will
become sick from this exposure
• forms of acanthamoebiasis:
✓ granulomatous amoebic encephalitis (GAE)
✓ Acanthamoeba keratitis (amoebic keratitis) (AK)
✓ disseminated form = systemic opportunistic infection that can occur both with
and without GAE (hematogenous dissemination, can affect the skin, sinuses,
lungs, and other organs independently or in combination)
✓ cutaneous form = skin infection
• GAE and disseminated forms are very rare and primarily affect immunocompromised
humans, but disseminated infection can also affect healthy children and adults
Diseases caused by Acanthamoeba infection
Acanthamoeba granulomatous amoebic encephalitis (GAE)
Clinical symptoms
• neurological manifestations and behavioural changes:
✓ mental status changes
✓ loss of coordination
✓ fever
✓ muscular weakness or partial paralysis affecting one side of the body
✓ double vision, sensitivity to light
✓ other neurologic problems
• rare form of Acanthamoeba infection (about 200
cases)
• chronic infection of brain and spinal cord
• spanning from several weeks to months
• humans with compromised metabolic, physiologic
or immunologic functions
A) Large coalescing necrotizing hemorrhagic lesions involving the insular cortex and putamen with extensive
perilesional oedema with compression of ipsilateral ventricle; B) dense vasculitis and inflammation; C) large
trophozoites aggregating around vessels D) in addition to thick-walled cysts.
https://doi:10.4103/0972-2327.128571
Pathology of Acanthamoeba GAE
https://doi.org/10.1186/s13000-018-0706-z
Histopathological findings of brain
biopsy. A-B) Necrotic tissue with
inflammatory cell infiltration and vessel
hyalinization. HE. C) Amoebic cysts. HE.
D) Trophozoites. HE. Both forms were
observed in necrotic tissues. E-F) Cysts
were also observed around blood
vessels. G) Cysts showed faint positive in
Periodic acid-Schiff stain (PAS) (arrows).
H-I) Immunohistochemical staining of
cysts – positive staining with antiserum
against Acanthamoeba (H), but negative
for Balamuthia (I).
Pathology of Acanthamoeba GAE
Diagnosis of Acanthamoeba GAE
✓ localised necrotic foci of infection in brain
tissue by neuroimaging
✓ definitive identification of amoebae upon
brain biopsy or at autopsy and microscopic
visualisation of trophozoites or cysts in
tissue sections, cultivation of amoebae
✓ molecular methods
Cytological findings of Acanthamoeba in CSF. Giemsa staining
of a trophozoite (arrow), lymphocyte (arrowhead).
IFA of Acanthamoeba
Pathology of disseminate acanthamoebiasis
Histopathological findings of the
right lung. A-B) Gross appearance of
coronal section of lung. Greyish lesion
with clear boundary was observed in the
upper lobe of the right lung. C) Very lowpower
field of the lung. Necrotic lesion
with clear boundary was observed. D-E)
High-power field of necrotic lesion in the
right lung. Amoebic cysts were observed
in a part of necrotic lesion (D) and
showed faint positive in PAS (E).
https://doi.org/10.1186/s13000-018-0706-z
• acute localised infection of cornea
• in immunocompetent individuals following corneal trauma
or as the result of poor hygiene in the care of contact
lenses or contact lens cases
• typically, 1 eye infected
• 1974 UK and USA: 3 cases
• 2004 > 3000 cases
• 1995: first case in the Czech Republic
• therapy with variety of drugs
Acanthamoeba keratitis (AK)
corneal ring infiltrate
• 3 per 100,000 and around 85 % of cases
occur in people who wear contact lenses
• exposure of the eye to contaminated water
• tap water should not be used to rinse
contact contact lenses
• corneal abrasion
• clinical symptoms: watering of eyes, eye
pain with photophobia, blurred vision and
irritation are common
• cysts in cornea
Acanthamoeba keratitis (AK)
A) Recent mention of Acanthamoeba keratitis (AK) in leading news media and news outlets after an outbreak of AK in the UK.
A similar epidemic of AK has occurred in the USA in the past. B) Superiority of FDA-approved drugs that have proven to kill
amoeba trophozoites and cysts over novel chemicals and biocides (B1). The FDA-approved drugs would need to be tested only
in human eye, as their safety studies have been completed in the past (B2). Note the effects of one of the FDA-approved drugs
on Acanthamoeba trophozoites as compared to control. DOI: 10.1038/s41433-018-0306-x
Cutaneous form of acanthamoebiasis
• nodular skin lesions
• HIV / AIDS patients
• disseminated skin form during GAE
Balamuthia mandrillaris
• free-living amoeba naturally found in the environment
• 1986 first isolation from brain of a mandrill baboon that died in
San Diego Wildlife Park
• larger than Acanthamoeba or Naegleria
• causing GAE (BAE) in humans and animals
• infection reports primarily originate from America, limited cases
from Asia, Australia, and Europe
• pleomorphic trophozoite (30-120 μm) with lobopodia and a single nucleus
• cyst - wall formed by a thin, wavy ectocyst, fibrous mesocyst and a thick round
endocyst; cytoplasm is filled with numerous pinocytotic vacuoles and/or vesicles
https://www.youtube.com/watch?v=B-GfKM759p0
Life cycle of Balamuthia mandrillaris
https://www.youtube.com/watch?v=lwgZ_wECJ_4
• immunocompromised people, including AIDS patients and intravenous drug users,
but also immunocompetent patients
• chronic disease - weeks to as long 2 years, more than 200 cases worldwide
• can infect the skin, brain and other organs of the body
• disease can begin with a skin wound and can progress to the brain 
granulomatous amoebic encephalitis (GAE)
• early symptoms of GAE: fever, headache, vomiting, lethargy, nausea
• other signs of GAE: mental health changes, seizures, weakness, confusion, partial
paralysis, difficulty speaking or walking
• disease might appear mild at first but can become more severe over weeks to
several months - often fatal, with a 90% death rate
Symptoms of balamuthiasis
✓ lesions in neuroimaging
✓ cultivation
✓ histology
✓ immunological detection
✓ molecular methods
Diagnosis of balamuthiasis
Balamuthia GAE diagnosis can be difficult
because symptoms are not specific to GAE
Pathology of Balamuthia GAE
Balamuthia mandrillaris in brain of
Bornean orangutan. A-B) Right dorsomedial
cerebral hemisphere is enlarged and distorted
by oedema, haemorrhage, malacia and
meningoencephalitis. that compresses the
right lateral ventricle and abuts the corpus
callosum. C) Intralesional, often perivascular,
trophozoites (*) admixed with haemorrhage
and oedema. D) Trophozoites have nuclei
with up to four nucleoli (arrow), and there are
rare amoeba cysts (circled). HE.
https://doi.org/10.1007/s10329-020-00860-z
Pathology and tretatment of Balamuthia GAE
A) Cutaneous lesion on the right knee observed in February
2006 showing an indurated and violaceous plaque covering the
entire knee with 2 papular lesions. B) Skin biopsy specimen
showing a dense inflammatory infiltrate of the dermis with
granulomas. An amoebic trophozoite is observed, with a nucleus
that has a large, central nucleolus and vacuolated cytoplasm.
HE. C) MRI obtained 7 days after the onset of neurologic
symptoms (June 2007) showing hypersignal in the left temporal
lobe. D) MRI (June 2007) showing a ring-enhancing lesion in the
left temporal lobe. E) Follow-up of the left knee lesion 1 week
after the patient had commenced treatment with miltefosine,
albendazole, and fluconazole. Lesions abruptly changed,
developing a scaly and crusty surface. F) MRI obtained 5
months after the start of treatment, showing significant
improvement on the neurological lesions without evidence of
contrast enhancing. G) MRI image 4 months after completion of
treatment, showing the disappearance of the brain lesions. H)
Follow-up of the healed left knee lesions (May 2008).
https://doi.org/10.1086/653609
Cutaneous and neurological
involvement !!!
https://doi.org/10.1111/j.1574-695X.2007.00232.x
Comparative characteristics of free-living amoebae as etiological agents of amoebic encephalitis and keratitis
genus Entamoeba
• small amoebae, with a single nucleus and typically a single lobose pseudopodium
• flagella and centrioles absent
• reduced Golgi
• mitosomes instead of classical mitochondria
• uninucleated trophozoites convert into cysts = encystation
• number of nuclei in the cyst varies from 1 to 8 among species
• one of the characteristics used to distinguish species
• several species are found in humans and animals
Conosa: Archamoebidae
morphology of nuclei in cysts
peripherally distributed chromatin
karyosom = endosom
Morphological characteristics of Entamoeba cyst
E. coli Homo 8 nuclei
E. dispar
E. histolytica Homo
E. hartmani
E. moshkovskii free-living, Homo
E. invadens reptiles
E. ranarum frogs
E. gingivalis Homo no cyst, originally 4 nuclei
E. chattoni apes 1 nucleus
E. polecki Homo, Sus
4 nuclei
group „histolytica“ - nucleolus centrally
E. histolytica
E. dispar
E. moshkovskii
E. hartmani
E. invadens
E. ranarum
group „coli“ - nucleolus eccentric
E. coli
E. muris
E. gallinarum
E. cuniculi
group „gingivalis“
• nucleus „histolytica“
• no cysts
• originally 4 nuclei
group „bovis“
E. bovis
E. ovis
E. polecki
E. chattoni
Morphological characteristics of Entamoeba cyst
genus Entamoeba – group „histolytica“
• intestinal trophozoites (10-60 μm vs. 4-12 μm in E. hartmanni)
✓ eruptive lobopodia
✓ ring of peripheral granules at inner surface of nuclear membrane
• cysts (10-20 μm) with 4 nuclei
E. dispar
• non-pathogenic
• formerly "non-pathogenic strains
of E. histolytica"
E. moshkovskii
• non-pathogenic
E. hartmanni
• non-pathogenic
E. histolytica
• potentially pathogenic
https://www.youtube.com/watch?v=d5b4eNhIhgQ
https://www.gettyimages.ae/detail/video/entamoeba-histolytica-parasites-stock-video-footage/618597219
Amoebic dysentery due to Entamoeba histolytica
• infecting humans (about 50 million people worldwide) and other primates
• mammals such as dogs and cats can become infected transiently
• previously, 10 % of the world's population was thought to be infected, but these estimates
preceded the discovery that at least 90% of these infections were caused by E. dispar
• about 10-20 % of infection with E. histolytica causes disease - in response to unknown
stimuli, trophozoites move through the mucus layer and start the pathological process
• trophozoites - forma minuta x forma magna (erythrophagocystosis)
✓ heat stress, physical exertion
✓ constriction of visceral vessels
✓ abnormal function of intestinal
mucosal cells
✓ disruption of intestinal biocenosis
✓ hypoxia
✓ change in the redox potential of
the intestinal mucosa
Amoebic dysentery due to Entamoeba histolytica
Transmission via ingestion of
food and water contaminated
with cysts, which excyst in small
intestine to the trophozoites that
colonise the large intestine
https://www.youtube.com/watch?v=EEFkIQjt8hw
New concept of amoebic dysentery due to E. histolytica
• Entamoeba histolytica, is the causative
agent of amoebic dysentery and amoebic
liver abscess (entamoebiasis)
• one of the leading causes of death from
parasitic diseases
• closely related E. dispar is morphologically
indistinguishable
• E. dispar is a commensal - not causing
disease in humans, even in
immunocompromised individuals
• highly prevalent in areas of poor sanitation
Morphologically-identical species of
Entamoeba, including E. dispar, E.
moshkovskii and E. bangladeshi,
are generally not associated with
disease although investigations into
pathogenic potential are ongoing.
Amoebic dysentery due to Entamoeba histolytica
• about 10-20 % of people infected with E. histolytica become sick from infection
• majority of infections restricted to intestinal lumen (“luminal amebiasis”) are asymptomatic
Clinical symptoms
• severe dysentery, stomach pain and cramping, bloody stools, fever
• amoebic colitis, or invasive intestinal amebiasis, occurs when the mucosa is invaded
• severe chronic infections may lead to further complications - peritonitis, perforations,
formation of amoebic granulomas (ameboma)
• rarely, E. histolytica invades other organs - liver abscesses are the most common
manifestation of extraintestinal amebiasis
• pleuropulmonary abscess, brain abscess, and necrotic lesions on the perianal skin and
genitalia have also been observed
flask ulcer
Amoebas (blue) in the intestinal tissue of mice (green).
Amoebas destroy the intestinal cells in order to penetrate
further into the body. If they get into the bloodstream, they
attack other organs. If left untreated, the infection is fatal. The
parasites can be fought with antibiotics.
submucosa
muscularis mucosae
mucosa
Mucosa invasion by Entamoeba histolytica
Invasion of the colonic and caecal mucosa by E. histolytica
SEM of intestinal amebiasis in a guinea pig. A)
Trophozoites of E. histolytica adhere preferentially to the
elevated interglandular epithelium. B) Note the small
interglandular region of microinvasion in the early
invasive lesion with superficial ulceration. C) In a more
advanced stage of invasion, numerous trophozoites
penetrate a colonic ulcer.
Experimental intestinal amebiasis in a guinea pig. An
invading E. histolytica trophozoite proceeds through the
interglandular epithelium. A large pseudopod is extended
by the parasite during penetration to the lamina propria. A
semithin section stained with toluidine blue is shown.
https://doi.org/10.1128/CMR.13.2.318
Pathology of intestinal amoebiasis due to E. histolytica
Human intestine with acute
amoebic colitis.
Histologic analysis of amoebic colitis. A) Trophozoites of E. histolytica ingesting
erythrocytes (arrows). HE. B) Numerous amoebic trophozoites on the mucosal surface. PAS.
Endoscopic features of amoebic colitis. A) Ulcers in the rectum. B) Multiple erosions
with exudates surrounded by oedematous mucosa in the sigmoid colon.
Patient with amoebic colitis. A) Intestinal ulcers. B) Amoebas within the lamina propria (arrows) surrounded by
inflammatory infiltrate of neutrophils. C) Invasion of intestinal mucosa by trophozoites. IHC of trophozoites (brown) using
anti–E. histolytica macrophage migration inhibitory factor antibodies.
Pathogenesis of intestinal amoebiasis due to E. histolytica
https://doi.org/10.1007/s40588-019-0113-6
1. Secreted E. histolytica macrophage migration inhibitory
factor (EhMIF) promotes mucosal inflammation.
2. E. histolytica–induced inflammation results in increased
production in matrix metalloproteinases (MMPs) which
break down extracellular matrix (ECM) in gut to promote
cell migration.
3. Infiltrating inflammatory cells generate oxygen free
radicals (ROS) which are capable of killing parasites. ROS
are also responsible for collateral tissue damage during the
inflammatory period.
4. Amoeba invades the intestinal mucosa by evading and
exploiting the host immune system.
5. Contact-dependent cell killing by E. histolytica.
6. Elevated levels of Prevotella copri (associated with gut
inflammation) increases the risk of colitis.
https://doi.org/10.1016/j.pt.2004.10.009
• adherence - lectin binding to galactose and N-acetylgalactosamine sugars on the
surface of the epithelial cells
• loosening of the epithelial layer - several enzymes such as pore forming proteins,
lipases, and cysteine proteases
• normally used to digest bacteria in food vacuoles
• causing lysis of epithelial cells by inducing cellular necrosis and apoptosis
• phagocytosis via amoebostome
Pathogenesis of intestinal amoebiasis due to E. histolytica
http://dx.doi.org/10.1136/thx.2004.021014
https://doi.org/10.1016/S0272-5231(01)00008-9
https://doi.org/10.1186/s40249-018-0419-2
Primary pulmonary amoebic abscess in a patient with pulmonary
adenocarcinoma. Pathological examination of the lung showing
trophozoites (arrows) of E. histolytica. A-B) HE. C-D) PAS.
Thoracic entamoebiasis
Primary plmonary amoebiasis presenting as superior vena cava
syndrome due to large mass in superior lobe of the right lung.
A-B) Postero-anterior radiographs and C-D) high resolution
computed tomographic scans of the thorax showing significant
enlargement of the mass in one day (B, D compared to A, C). E-F)
Lung section showing necrotic tissue which reacted with anti-E
histolytica antibodies (IFA). Note a small number of amoebae with
green fluorescence. F shows a single amoeba.
Pleuropulmonary amebiasis is common, while
pericardial amebiasis the rare form of thoracic
form. Malnutrition, chronic alcoholism and atrial
septal defect with left to right shunt contribute to
development of pulmonary amoebiasis.
https://doi.org/10.1016/j.jhep.2021.03.018
Trogocytosis in Entamoeba histolytica
A) Previous model for cell killing, in which human cell attachment
is followed by human cell killing and ingestion.
B) Model for amoebic trogocytosis in cell killing, in which
attachment is followed by ingestion of fragments of human cell
material, leading to human cell death. Following cell killing,
amoebae dissociate from the dead cells.
C) Model for phagocytosis of pre-killed human cells, which are
ingested whole.
https://doi.org/10.1038/nature13242
Trogocytosis in Entamoeba histolytica
https://www.youtube.com/watch?v=wT5xqFm359I
https://www.youtube.com/watch?v=2JGKGXrja5o&t=11s
Amoebic dysentery due to Entamoeba histolytica
Diagnosis
✓ differential diagnostic
✓ clinical signs, imaging methods
✓ direct faecal smear (DFS) and staining (but
does not allow identification to species level
✓ enzyme immunoassay (EIA)
✓ indirect hemagglutination (IHA)
✓ antigen detection - monoclonal antibody
✓ PCR for species identification
✓ cultivation
Therapy
✓ metronidazole, paramomycin, diloxanide
fluroate
Entamoeba coli
• most common human amoeba,
also in primates and dogs
• about 15 % of Czech population
Entamoeba gingivalis
• non-pathogenic, inhabiting human oral cavity
• common in individuals with poor oral hygiene or periodontal disease
• occasionally other sites (female genital tract with use of intrauterine device)
• often found in conjunction with periodontal disease, but no causative association so far
identified
Trophozoites of E. gingivalis. Note the
ingested host material - epithelial cells and
leukocytes (arrow). Papanicolaou’s stain
Thank you for your attention ☺
Lectures
✓ Introduction: BPP 2022 I
✓ Euglenozoa (Excavata): BPP 2022 II
✓ Fornicata / Preaxostyla / Parabasala (Excavata): BPP 2022 III
✓ Apicomplexa I (SAR): BPP 2022 IV
✓ Apicomplexa II (SAR): BPP 2022 V
✓ Amoebae (Excavata, Amoebozoa): BPP 2022 VI
 Ciliophora, Opalinata (SAR): BPP 2022 VII
• Pneumocystis (Opisthokonta, Fungi): BPP 2022 VIII
• Microsporidia (Opisthokonta, Fungi): BPP 2022 IX
• Myxozoa (Opisthokonta, Animalia): BPP 2022 X