The Amoebas

1
The Amoebas
2
Order Amoebida

• Family Endamoebidae
• Parasitic or commensals of digestive system
• Includes Entamoeba, Endolimax and Iodamoeba

3
Entamoeba

• Have a nucleus that is vesicular with small
  endosome at or near the center (concentric)
• Chromatin is around the periphery of the membrane
• Cytoplasm is usually full of food vacuoles
• Golgi and mitochondria are absent
• Have helical bodies in some trophozoites
• 40 distinct ribonucleoproteins
• Crystalize into chromatoidal bodies or bars in
  the cyst forms
• Blunt or splintered ends based on the species

4
Entamoeba histolytica

• 3rd most common cause of parasitic deaths
• Causes severe diarrhea
• 2 sizes
• Smaller sizes trophozoites and cysts are not
  associated with disease
• E. hartmanni
• Larger sized trophozoites and cysts are
  pathogenic
• E. histolytica

5
Life Cycle

• Trophozoite
• Precyst
• Troph release undigested food, secretes a hyaline
  cyst wall to become cyst
• Cyst
• Metacyst
• Has 4 nuclei
• Metacystic trophozoite
• Metacyst divides into 8 small amebulas which are
  small trophs
• Precyst, Cyst and Metacyst forms as stool
  dehydrates and dries, not in diarrhea or in the
  tissues
• Trophozoite in large intestine ? cyst in feces ?
  ingested ? trophozoite in large intestine

6
E. histolytica Trophozoites

• Found in loose stools mainly
• Nucleus with a central endosome and a fine
  peripheral ring of chromatin distinguishes this
  parasite from E. coli
• Charcot-Leyden crystals, representing the
  crystallized contents of granules from eosinophil
  leukocytes may also be found in a fecal smear
• Capable of causing ulcerative colitis, resulting
  in severe dysentery, as well as extra-intestinal
  amebiasis, including fatal brain infections.

7
E. histolytica Trophs
8
E. histolytica Cysts

• Stool smear
• Cysts found mainly in formed stools
• Infective stage
• Chromatoidal bars (C), when present in immature
  cysts (precyst), usually have blunt ends, versus
  splintered ends in cysts of E. coli
• Disappear as cyst becomes older

9
E. histolytica Cysts

• Cysts have four or fewer nuclei
• Although all four nuclei may not be visible in
  the same plane, they can be counted by carefully
  adjusting the fine focus control (N1-N4, second
  row).

10
E. histolytica Biology

• Trophozoites
• Live and multiple indefinitely in the crypts of
  the mucosa of the large intestine, eating
  bacteria
• Can invade the tissue when proteolyze the mucosal
  cells pathogenic and non-pathogenic
• Uses filopodia for endocytosis, pinocystosis,
  attachment, penetration of tissue, release of
  cytotoxic substance and contact cytolysis of host
  cells
• Move in the blood to other organs such as liver,
  lung and skin once it penetrates the intestinal
  mucosa
• Trophs are NOT infective
• Cysts
• Leave in large numbers, host is usually
  asymptomatic or infected with small numbers
• Cysts are not resistant to drying and temperature
  fluctuations but can withstand the chlorine
  levels used in H2O purification
• Can withstand the stomach acid but in alkaline
  small intestine, the metacyst activates and can
  tear through the cyst wall, divides into amebulas
  and is moved into the cecum
• Metacystic troph needs to contact mucosa to
  survive and cause infection

11
Intestinal Lesions

• Usually develop in cecum, appendix or upper large
  intestine
• Connect to lumen but spread laterally
• Late infection may be complicated by bacteria,
  erode through wall and get in the blood
• Can form a granulomatous mass in the wall of the
  intestine called an Ameboma
• Result of cellular response
• Lesions in the liver may have necrosis but are
  bacterially sterile hepatic amebiasis
• Lung amebiasis is 2nd most common
• May be primary or metastatic from the liver by
  way of through the diaphragm

12
Symptoms

• Intermitent diarrhea, cramps, vomitting, general
  malaise slowly developing
• More severe infection with higher parasite load,
  pain in abdomen, fulminent diarrhea and
  dehydration chronic form that continues to get
  worse
• Acute amebic dysentary has headache, fever,
  severe abdominal cramping with prolonged
  straining at the stool
• Very liquid feces with bloody mucous
• Possible death from peritonitis, cardiac failure
  and exhaustion

13
Diagnosis and Treatment

• Diagnosis
• See troph or cyst in the stool sample
• May need to do several consecutive days
• Need to rule out E. dispar, a non-pathigenic
  parasite
• Treatment
• Metronidazole

14
Epidemiology

• Can be found everywhere
• Clinical amebiasis is mostly tropical and
  subtropical
• Transmitterd from anal to oral contact
• Bas bathroom and handwashing techniques

15
Entamoeba coli

• Co-exists with E histolytica
• Troph hard to distinguish from E histolytica
• Commensal with no tissue lysis must identify
  because presence indicates fecal-oral
  contamination
• Important to make the correct diagnosis
• This requires no treatment
• Life cycle identical to histolytica

16
E. coli Trophs

• Stool smear
• Distinguish from E. histolytica by the usually
  eccentric location of the endosome and the
  relatively coarser, larger granules in the ring
  of peripheral chromatin
• Found mainly in loose stools.

17
E. coli Cysts

• Stool smear
• Presence of more than four nuclei (actually,
  eight are present in mature cysts)
• Chromatoidal bars (C) in immature cysts have
  splintered ends, versus blunt ends in cysts of E.
  histolytica
• Found mainly in formed stools
• Infective stage.

18
E. gingivalis

• Found in human, dog, cat and monkey
• Dwells only in the mouth
• Found on the surface of teeth, gums and gingival
  packets, may also be in the tonsil crypts
• 95 with unhealthy mouth and 50 with healthy
  mouth
• Present in all populations and is a commensal
• Found only as a troph, have blunt pseudopodia for
  rapid movement, small nucleus, nearly central
  endosome and chromatin on the inner surface of
  the membrane

19
Endolimax nana

• Found in the large intestine near the cecum
• Commensal must identify because presence
  indicates fecal-oral contamination
• Has a thin layer of ectoplasm around the
  endoplasm, short blunt pseudopodia very slow
• Small nucleus the a large endosome, centrally to
  eccentrally located
• Often have large glycogen vacuoles
• Life cycle is similar to other Entamoeba

20
E. nana Trophs

• Stool smear
• Small nuclear size and prominent endosome
• Infection occurs when the cyst is ingested
• Found mainly in loose stools

21
E. nana Cysts

• Stool smear
• Small size and presence of up to 4 nuclei with
  prominent endosomes
• Found mainly in formed stools
• Infective stage

22
Iodamoeba buetschlii

• Only a single species
• Infects humans, other primates and pigs
• Life cycle is same as other amoebas
• Nucleus has light staining granules between
  endosome and nuclear membrane as well as
  achromatic strands

23
I. buetschlii Troph

• Stool smear
• Prominent endosome and numerous cytoplasmic
  vacuoles
• Considered to be harmless
• Important to identify because it is an indicator
  of fecal-oral contamination
• Found mainly in loose stools. Infection occurs
  when the cyst is ingested.

24
I. buetschlii Cysts

• Stool smear
• Found mainly in formed stools
• Oval shape nucleus, prominent endosome and large,
  single, glycogen-filled vacuole
• Cell is retracted from the cyst wall in one
  specimen (arrow)
• Infection occurs when the cyst is ingested

25
Acanthamoeba culbertsoni Troph

• Culture smear
• Spike-like rhizopods near the apex of the
  organism
• Some are found as opportunistic parasites of
  immunosuppressed individuals and in
  immunocompetent persons suffering trauma to the
  conjunctiva of the eye or using contaminated
  contact lens cleaning solutions
• In immunosuppressed individuals, it forms slowly
  spreading granulomas in the visceral organs
• Eye infection may require surgical removal of the
  eye
• Cyst is the infective stage
• Life cycle
• trophozoite in soil?cyst in soil ?introduced into
  the eye ? trophozoite in tissues ?cyst in tissues

26
Nalgeria fowleri

• Causes primary amebic meningoencephalitis (PAM)
• Has a flagellate and amoeba form and it rapidly
  switches from one to the other
• Flagellate stage 2 flagella, no pseudopodia,
  vesicular nucleus with large endosome and
  peripheral granules
• Ameboid stage single blunt pseudopodium
• PAM is gotten when swimming in infected water and
  is usually diagnosed at autopsy

27
N. fowleri Life Cycle

• cyst in bottom mud ? trophozoite in bottom mud ?
  biflagellated cell ? inhaled into nasal cavity ?
  trophozoite in nasal cavity ? migrates along
  olfactory nerve ? trophozoite in brain

28
Brain Section
500 mm
10 mm

• Individual trophozoites within necrotic zone,
  each with a prominent endosome