Intestinal Amoeba

Protozoa

microscopic one celled organism that can be free living or parasitic in nature

• multiplies in humans which contributes to their survival

• permits serious infections to develop from just a single organism

identification criteria for intestinal amoeba species

• size

• number of nuclei

• nuclear structure

  • karyosome, peripheral chromatin, chromatoidal bar, life cycle stage

Protozoa

microscopic one celled organism that can be free living or parasitic in nature

• multiplies in humans which contributes to their survival

• permits serious infections to develop from just a single organism

identification criteria for intestinal amoeba species

• size

• number of nuclei

• nuclear structure

  • karyosome, peripheral chromatin, chromatoidal bar, life cycle stage

karyosome

(endosome) a mass of chromatin

peripheral chromatin

nuclear DNA not included in the karyosome

chromatoidal bar

a rod-like internal structure outside of the nucleus of an amoeba in its cyst phase usually comprised of ribonucleoproteins in crystalline form

trophozoite

motile stage that feeds, multiplies, and maintains colony within the host

cyst

immotile stage protected by a resistant cyst wall formed by the parasite and can be readily transmitted to a new host (infectious)

general life cycle of intestinal amoeba

• direct fecal oral transmission in food or water with no intermediate host

• infectious cyst stage is ingested

• organisms excyst in the intestinal tract

• multiplication through binary fission

• colonization of fecal area by trophozoites

intestinal amoeba treatment is only given in cases of

Entamoeba histolytica (most common pathogen)

intestinal amoeba carrier treatment

metronidazole (luminal amebicide)

invasive intestinal amebiases treatment

systemic drugs like lodoquinol and paromomycin

“cyst passers”

asymptomatic colonization with Entamoeba hisstolytica

Amebic dysentery

colitis caused by Entamoeba histolytica with flask shaped ulcers in the colon

Extraintestinal amebiases

caused by Entamoeba histolytica and can disseminate and cause disease to liver, lung, pleural abscesses, peritonitis, skin, and genital lesions

• lesions are described as “anchovy paste”

Entamoeba histolytica trophozoite

• 15-25 um

• single bull’s eye nucleus with central karyosome

• can contain ingested RBCs

Entamoeba histolytica cyst

• 10-20 um

• 4 nuclei

• when cyst matures, can have central chromatoidal body

Entamoeba dispar

• originally thought to be a secondary strain of Entamoeba histolytica but is a different, non-pathogenic species

Entamoeba dispar vs. Entamoeba histolytica

cannot distinguish between the two, unless RBCs are engulfed

• non-pathogenic Entamoeba dispar does not engulf RBCs

• pathogenic Entamoeba histolytica does engulf RBCs

Entamoeba hartmanni troph

• 4-12 um

• small, central karyonsome

• even, peripheral chromatin

Entmoeba hartmanni cyst

• 5-10 um

• small, central karyosome

• 1-4 nuclei

• cigar shaped chromatoidal bar (criss-cross)

• even distributed chromatin

Entamoeba coli troph

• 15-50 um

• large, eccentric karyosome

• uneven chromatin

• “dirty” vacuolated cytoplasm

• bacteria in cytoplasm

Entamoeba coli cyst

• 10-25 um

• 2-8 nuclei

• large, eccentric karyosome

• splinter shaped chromatoidal bars

Endolimax nana troph

• 5-12 um

• prominent “blot-like” karyosome

• no peripheral chromatin

Endolimax nana cyst

• 5-12 um

• usually oval shaped

• 4 nuclei

• prominent karyosome in nuclei

• granular, vacuolated cytoplasm

Iodamoeba butschlii troph

• 6-20 um

• no peripheral chromatin

• achromatic granules around large karyosome

• vacuolated cytoplasm

Iodamoeba butschlii cyst

• 6-15 um

• prominent glycogen vacuole

• vacuolated cytoplasm

• ONLY amoebic cyst with ONE nucleus

Blastocystis hominis cyst

• multiplies by binary fission

• 3-5 um

• large vacuole surrounded by several small nuclei

• can be confused with yeast

• no troph form, only spherical form seen