Intestinal protozoa Flashcards
4 classes of intestinal protozoa
- Amoebae
- Ciliates
- Flagellates
- Coccidia
Amoebae
Naked, loose, pseudopod-forming. They are abundant soil dwellers, rich organic debris.
Ciliates
Microscopic appendages extending from the surface of the cell. Only one pathogenic ciliate
Flagellates
Free-living, whip-like appendages, pathogenic for humans and animals
Coccidia
Subclass of protozoa, epithelia cells of intestinal tract, liver, and other organs
Entamoeba histolytica
Pathogenic amoeba, associated with intestinal and extra-intestinal infections. Worldwide distribution, the highest rate of amebiasis is in developing countries (lack of appropriate sanitation, sewage contamination in water). Infection occurs through ingested of mature cysts from fecally contaminated food, water, or hands. In developed countries, male homosexuals, travelers and recent immigrants, and institutionalized populations. This species is indistinguishable from many non-pathogenic amoeba species
Entamoeba histolytica clinical presentation
Clinical presentation. 90% of infection is asymptomatic. Patients almost never become symptomatic, they excrete cysts for a short time, you do not find trophozoites within the RBCs. Patients have negative occult blood, weak negative antibody titers. When symptomatic, patients have have intestinal or extraintestinal disease
Intestinal disease in E. histolytica
With intestinal amebiasis, there is a 1-4 week incubation, invades the tissues causing fever, ulceration, and pain. Patients can develop invasive disease- dysentery or fulminating colitis= 90% of disease. Possible bloody stools or tenesmus. Also find amebic appendicitis or ameboma of the colon
Extraintestinal infection- E. histolytica
2-8% of cases disseminate, the most common is the liver with abscess formation. Rare brain abscess (from the liver), cutaneous disease= amebiasis cutis, pleuropulmonary abscess (from the liver) and genital amebic lesions
E. histolytica life cycle
- Cysts and trophozoites are passed in feces
- Mature cysts are ingested by the human host
- Excystation occurs in the small intestine
- Trophozites are released, can invade the intestinal mucosa and move to the liver, brain, or lungs
- Trophozoites multiply by binary fission, producing trophozoites and cysts.
- Both stages are released in the stool, but only cysts survive and are ingested
Trophozoites
Trophozoites are found in intestinal amebae and measure between 10-60 micrometers. They are elongated in diarrheal stool and have finger-like pseudopodia. Have a single nucleus that must be stained to visualize. Peripheral chromatin is uniform in size, fine, and may be beaded. A karysome is small, compact, and centrally located, may be eccentric. The cytoplasm has a clear, ground glass appearance
Cysts
Found in intestinal amebae, measure 10-20 micrometers. Immature cysts have 1 to 2 nuclei while mature cysts have 4 nuclei (E. coli has 8). Peripheral chromatin is fine and uniformly distributed, and the karysome is small, compact, and centrally located. Cytoplasm and chromatoidal bodies have long blunt ends and are round to oval. Glycogen vacuoles can be diffuse or even absent
E. histolytica vs nonpathogenic E. coli
Main differences- in E. histolytica trophozoites ingest RBCs (this is very rare in the nonpathogenic form). This is the only morphologic characteristic that can be used to differentiate E. histolytica from the nonpathogenic entamoeba. However, this doesn’t happen in every patient. E. histolytica cysts contain only 4 nuclei while cysts from the nonpathogenic form contain 8 nuclei. For E. histolytica, chromatin is beadlike, for E. coli, it is chunky/blotchy
E. histolytica vs. E. dispar
E. dispar is nonpathogenic. We are unable to differentiate based on morphology, but they are different species. There are some PCR-based and DNA sequence assays to differentiate. Very few differences have been identified
E. moshkovskii
Non pathogenic, only difference with histo/dispar is physiological, identified only by molecular methods
E. bangladeshi
Non pathogenic, can only differentiate from histo/dispar by a small subunit rRNA gene sequence. It has been found in asymptomatic and symptomatic individuals
E. polecki
Non pathogenic, can be identified only by molecular methods, troph morphology is similar to that of other species. Originally isolated from the intestines of pigs and monkeys
E. hartmanni
Can differentiate from histo/dispar based upon size, as cysts are 5-10 micrometers, trophs are 4-12 micrometers. A calibrated microscope must be used for measurement since there is slight overlap. First thought of as an animal pathogen and could transform from non pathogenic to the pathogenic form
Endolimax nana trophozoites
A nonpathogenic amoeba. Trophozoites are 6-12 micrometers. They have a single nucleus, irregularly shaped, with a large karysome. The nucleus has no peripheral chromatin. The cytoplasm is often highly vacuolated, containing bacteria. Difficult to distinguish from those of Iodamobea buetschlii
Endolimax nana cysts
Cysts can be spherical to ellipsoidal. They are 5-10 micrometers, mature cysts have 4 nuclei. They have large karysomes and no peripheral chromatin. The cytoplasm may contain glycogen but lacks chromatid bodies
Iodamoeba buetschlii trophozoites
8 to 20 μm, single nucleus with a large, central karyosome. Refractile, achromatic granules around karyosome. Cytoplasm is coarsely granular, vacuolated with bacteria, yeasts or
other materials.
Iodamoeba buetschlii cysts
Spherical to ellipsoidal, and measure 5-20 μm. Single nucleus that is not visible in either unstained or iodine-
stained wet mounts. Nucleus contains a large, usually eccentric karyosome. Achromatic
granules may or may not be present around the karyosome.
Iodamoeba buetschlii diagnosis
Large glycogen vacuole (iodine stained). Glycogen vacuole does not stain with trichrome, but still visible.
Blastocystis hominis
There is a question regarding the true pathogenic nature of this organism. It is the causative agent of intestinal disease when no other pathogen present. Increased in immunocompromised patients. It was previously considered a yeast but is now considered a multicellular protist. In absence of other pathogens with symptoms, symptoms include diarrhea, abdominal pain, nausea, fever, vomiting
Why is Blastocystis hominis considered a protist? (3)
- Only grows in presence of bacteria
- Produces pseudopods and ingests bacteria
- No growth on fungal media
Blastocystis hominis diagnosis
Molecular methods – sequence of SSUrRNA gene. Serology – high titers suggest pathogenicity
Blastocystis hominis cysts
Forms cyst-like structures- they are spherical cells, vary in size (5 to 15μm). They have a central body, or “vacuole,” about 70% of cell, surrounded by a thin
rim of cytoplasm, as well as up to 6 nuclei
Staining of Blastocystis hominis
Vacuoles stain variably from red to blue in trichrome stain. You can quantitate the number of cyst in stool (rare, few, moderate, many). This method is controversial, but some physicians find a correlation with number and disease
Pathogenic intestinal flagellates (2)
- Giardia lamblia
- Dientamoeba fragilis
Nonpathogenic intestinal flagellates (2)
- Chilomastix mesnili
- Pentatrichomonas hominis
Giardia lamblia
Pathogenic, also known as G. intestinalis or G. duodenalis. Found worldwide, specifically in warm climates and in children. Infections can be asymptomatic or cause severe diarrhea/malabsorption. With acute giardiasis, the incubation period is 1 to 14 days (average of 7 days), illness lasts 1 to 3 weeks.
Giardia lamblia symptoms
Diarrhea, abdominal pain, bloating, nausea, and vomiting. With chronic giardiasis, the symptoms are recurrent and malabsorption and
debilitation may occur
Giardia lamblia diagnosis (3 methods)
- Fecal sample - ELISA for antigen most common
- Duodenal aspirate – motile trophozoite
- Trichromes, wet preps, newer molecular methods, DFA
Giardia lamblia life cycle
- Host swallows giardia cysts
- Giardia cysts are swallowed and enter the small intestine. Excystation occurs- each cyst releases 2 trophozoites, which feed off the host
- Trophozoites multiply by binary fission, split into 2 in the small intestine
- Trophozoites move into the colon. They undergo encystation and transform into cysts
- Cysts and trophozoites are found in the stool. Cysts are immediately infectious and can survive for months
