Protozoa

Protozoa

Protozoa: Amoebae

Subphylum Sarcodina

Single celled eukaryotes

Feed by engulfing particle

Move by Pseudopodia

Definitions

Trophozoite form

  • Motile, reproductive, feeding stage

Cyst form

  • nonmotile , resting stage that is resistant to environmental effects

Chromatoidal bars or bodies

  • Dark-staining cytoplasmic inclusion of chromatin

Endosome or Karyosome

  • Mass of organelles or mass of chromatin in the nucleus

Amoebae Diagnosis:

Motile trophozoites in fresh, warm, liquid stool

  • Wet mounts and iodine preps

Trophozoites &/or cysts in fixed smears

  • Trichrome stain

Trophozoites or cysts in other body tissues or fluids; serologic tests; ELISA

Pathogenic intestinal amoeba

  • Entamoeba histolytica

Nonpathogenic intestinal amoebae

  • Entamoeba coli
  • Endolimax nana
  • Iodamoeba butschlii
  • Entamoeba hartmanni

Free-living pathogenic amoebas

  • Acanthamoaba castellani
  • Naegleria fowleri

Differentiating the Amoebas

Shape of nucleus

Number of nuclei

Size

Shape

Inclusions

Entamoeba Histolytica

Amebiasis

Transmission by ingestion of cysts

  • Fecal-oral route of contaminated food

Intestinal disease

  • Asymptomatic or amoebic dysentery
  • diarrhea, cramping, abdominal pain

Disseminated

  • hematogenous spread to liver, spleen, lung, or brain

Microscopic Characteristics E. Histolytica

Trophozoite

  • 10-20 um
  • Irregular shape
  • Single nucleus with central karyosome
  • Ingested RBCs

Cyst

  • 10-20 um
  • Contain one, two or four nuclei with central karyosome
  • Rounded chromatoidal bars

*Side Note

Entamoeba hartmanni

  • Morphologically same as E. histolytica
  • Much smaller size (less than 10 um)

Entamoeba dispar & E. moshkovskii

  • Morphologically similar to E. histolytica

Non Pathogenic Amoebae

Entamoeba Coli

Very common commensal

Cysts

  • >10 um
  • Up to 8 nuclei with an eccentric karyosome
  • Pointed, sharp chromatoid bars

Trophozoite

  • Ingested bacteria
  • NO ingested RBCs

*Blastocystis Hominis*

Some source consider Blastocystis hominis to belong to the genus Stramenopiles

Brown algae, water molds, and diatom also members of this group

The exact life cycle is not completely known and as such changes continue to occur

Status of being a “true pathogen” remains controversial.

Potential pathogen

  • Recurrent diarrhea, abdominal cramping, anorexia, flatulence

Four forms

  • Ameboid
  • Granular
  • Vacuolar

Most commonly Identified

  • Cyst

Recovery of the vacuolar form

  • Morphologic characteristics
  • 5 to 15 um
  • Empty central body (green on trichrome)
  • Nuclear material in ring pattern between the central body and outer membrane

Comparison of Amebae

Free-Living Pathogenic Amoebas

Fresh and saltwater, soil, and decaying vegetation

Naegleria fowleri

  • Gains entry through nasal mucosa
  • Primary amebic meningoencephalitis (PAM)
  • Ameboid form found in CSF and tissues

Acanthamoeba

  • Inhalation of contaminated dust
  • Granulomatous amebic encephalitis (GAE)
  • Brain abscesses, keratitis, sinuses

Balamuthia mandrillaris

  • Found in soil, inhaling cysts or direct inoculation and organ transplant
  • GAE

Flagellates (Mastigaphora)

Flagella – provides locomotion

Axoneme – intracellular portion of a flagellum

Axostyle – rod that provides support in flagellates

Pathogenic Flagellates

Intestinal flagellates

  • Giardia lamblia
  • Dientamoeba fragilis

Vaginal flagellate

  • Trichomonas vaginalis

Blood & tissue flagellates

  • Trypanosoma sp.
  • Leishmania sp.

Non pathogenic Flagellates

Ganstointenitnal flagellates

  • Chilomastix mesnili
  • Trichomonas hominis

Giardia Lamblia

Most common diarrheal disease transmitted by contaminated water in U.S.

Transmission: contaminated water, fecal-oral route, oral-anal sex, etc.

Only human protozoa that reside in the duodenum

Giardiasis: “Travelers diarrhea,” beaver fever,” backpacker’s diarrhea”

Symptoms: Mild to severe diarrhea

Diagnosis: trophozoites or cysts in stool and biopsies, ELISA

Microscopic Characteristics

Trophozoites

  • Bilateral symmetry
  • Two nuclei
  • Eight flagella

Cysts

  • Oval
  • Two to four nuclei

Dientamoeba Fragilis

Assoc. With cases of diarrhea

No cyst form, only trophozoite

Trophozoite

  • Two nuclei (very dense central chromatin)

Trichomonas Vaginalis

Trophs live in vagina, urethra, epididymis, and prostate

No cysts stage

Transmission via sexual intercourse

Method of diagnosis

  • Wet mount
    • Urethral discharge, vaginal smear, or urine.
    • Observe “jerky” pattern of motility

Non Pathogenic Intestinal Flagellates

Intestinal & Urogenital Flagellates

Blood & Tissue Flagellates

Trypanosoma (tsetse fly)

  • T. brucei rhodesience
    • East African sleeping sickness
  • T. brucei gambiense
    • West African sleeping sickness

*Trypomastigote the diagnostic from observed in the blood

Trypanosoma cruzi

Central, South America, Cuba, Mexico, and now Florida, TX, California

Vector is the Triatoma or reduviid bug

Amastigote form observed in the tissues (heart)

Trypomastigote (characteristics “C” shape) may be found in the blood

Chagas’ disease

The disease can be mild, causing swelling and fever, or it can be long lasting. LEft untreated, it can cause congestive heart failure

Treatment for Chagas disease focuses on taking medications that kill the parasite and on managing symptoms

Blood & Tissue Flagellates

Leishmania

Vector sandfly (Phlebotomus spp.)

L. tropica

  • “Old world disease” boils

L. mexicana

  • “New world disease” or espundia

L. braziliensis

*all three produce cutaneous lesions, amastigote forms found in tissues

Leishmania Donovani

Spread beyond the cutaneous lesions to the internal organs

  • Spleen, liver, bone marrow

Amastigote forms (LD bodies) observed in tissues

Kala-azar

Ciliates: Ciliophora

Movement by cilia

Macronucleus & several micronuclei

Only pathogenic human ciliate

  • Balatidium coli (commonly infects hogs)
  • Largest human intestinal protozoa

Symptoms: asymptomatic or diarrhea with alternating constipation

Diagnosis

  • trophozoites or cysts in feces

B. coli Trophozoite (A) & Cyst (B)