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
Giardia lamblia trophozoites
Have 9-21um length, 5-15um width. Bilateral symmetry - Sucking disks (eyes) for attachment, 2 median parabasal bodies (mustache) associated with flagella. The central axostyle (face) is central attachment of flagella. On wet prep, they have a falling leaf motility
Giardia lamblia cysts
8-12um, oval shape. Mature cysts have 4 nuclei, a small karyosome that is centrally placed, no peripheral chromatin
Dientamoeba fragilis
Pathogenic, ameba-like intestinal flagellate, but is does not have a flagellum. Worldwide distribution. Has a high association with pinworm. The eggs of Nematode Enterobius
vermicularis are
infected with this flagellate. Patients are 9X more likely to have pinworm when have D.
fragilis
Dientamoeba fragilis life cycle
Dientamoeba fragilis symptoms
Symptoms that have been
associated with infection
include diarrhea, abdominal
pain, anorexia, nausea,
vomiting, fatigue, and weight
loss.
Dientamoeba fragilis trophozoite
5 to 12um, has an asymmetrical ameboid form. 80% contain 2 nuclei. Have prominent Karysomes that are fragmented into 4 to 8 granules. Have pseudopods for motility
Dientamoeba fragilis cysts
No stage identified to date. Food-borne or water transmission low/unlikely
Chilomastix mesnili
Nonpathogenic flagellated protozoan. Worldwide distribution. The presence of cysts and/or trophozoites in
stool specimens can
however be an indicator
of fecal contamination of
a food or water source,
and thus does not rule-
out other parasitic
infections.
Chilomastix mesnili life cycle
Chilomastix mesnili trophozoites
Pear-shaped, 6 to 24um length, 4 to 8um width. They have a single large nucleus, immediately beneath outer membrane. The flagella are difficult to visualize
Chilomastix mesnili cysts
Lemon-drop shaped, 6 to 10um length, 4 to 6um width. Have a distinct hyaline knob on one side. Single nucleus, small central Karyosome, cytostome = crook at end
Pentatrichomonas hominis
Nonpathogenic intestinal flagellate with worldwide distribution. Infection occurs after the ingestion of trophozoites in fecal contaminated food or water, or on fomites. The presence of trophozoites in stool specimens can however be an indicator of
fecal contamination of a food
or water source, and thus
does not rule-out other
parasitic infections.
Pentatrichomonas hominis life cycle
Pentatrichomonas hominis trophozoite
Teardrop-shaped, 7 to 15um length, 4 to7um width. Has a single nucleus, displaced from the outer membrane. There is an undulating membrane that covers the full length of organism
Pentatrichomonas hominis cysts
This organism does not have a cysts stage
Balantidium coli
Pathogenic intestinal ciliate- it is the only pathogenic ciliate. Worldwide, swine are animal
reservoir, human infections occur more frequently in these areas. Infrequent rodents, nonhuman primates. Causes Balantidiasis
Balantidium coli symptoms
Mostly asymptomatic. Symptoms when present include persistent diarrhea, occasionally dysentery, abdominal pain, and weight loss. Causes severe illness in
immunocompromised people
Balantidium coli life cycle
Balantidium coli trophozoites
Large size - 40 μm to 200 μm. Have cilia on the surface, bean-shaped macronucleus, smaller micronucleus
Balantidium coli cysts
Less frequently encountered. 50 μm to 70 μm, can invade tissue.
Intestinal Coccidia
Pathogenic, the life cycle of most requires an external intermediate host. Extra-intestinal life-cycle development is a cyst forming coccidia
Cryptosporidium species (2)
- Cryptosporidium parvum- cattle
- Cryptosporidium hominis
Cryptosporidium species
Intestinal pathogenic coccidia. The small intestine is the most common site, also including other digestive tract organs, the lungs, and the conjunctiva. Worldwide distribution, transmitted by infected food, water (chlorination does not kill), and report of aerosol inhalation. Asymptomatic infections to life-threatening illness. The incubation period is an average of 7 days (range 2 to 10 days)
Cryptosporidium species symptoms
Illness lasts 1-2 weeks. Symptoms- watery diarrhea, dehydration, weight loss, abdominal pain, fever, nausea and vomiting. Chronic and more severe in immunocompromised patients
Cryptosporidium species asexual multiplication
schizogony or merogony. Then sexual reproduction
– MALE = microgamonts
– FEMALE = macrogamonts
Cryptosporidium species sexual multiplication
Fertilization allows for oocyst to
develop & sporulation. Thin (autoinfect) and thick-walled
(excreted) oocysts
Cryptosporidium species life cycle
- Sporulated oocysts, containing 4 sporozoites, are excreted by the infected host in the stool
- Host consumes contaminated food/water, may be inhaled
- Excystation occurs after ingestion
- Sporozoites are released and parasitize the epithelial cells of the GI tract
- In these cells, parasites undergo asexual multiplication (schizogony/merogony)
- Then, they undergo sexual multiplication (gametogony) and produce microgamonts (male) and macrogamonts (female)
- Macrogamonts are fertilized by the microgametes- oocysts develop and sporulate in the infected host
- Zygotes give rise to 2 types of oocysts- thin walled and thick walled. Thick walled are excreted, thin walled are involved in the autoinfective cycle and are not excreted
- Oocysts are infectious upon excretion and allow for fecal-oral transmission
Cryptosporidium species infectious stage
Cryptosporidium species diagnostic stage
Cryptosporidium species oocysts
Rounded 4.2 to 5.4μm. Sporozoites are sometimes visible inside oocysts, indicating that sporulation has occurred. Oocysts staining is variable. Infections that are resolving see number of non-acid-fast oocysts
“ghosts.”
Cryptosporidium species diagnosis
Cryptosporidium species staining
Cyclospora cayetanensis
Intestinal coccidia, most common in tropical and subtropical areas. There have been 11 outbreaks in north America since 1990. The incubation period is 1 week
Cyclospora cayetanensis symptoms
Watery diarrhea, which can
be severe. Other symptoms
include anorexia, weight loss,
abdominal pain, nausea and
vomiting, myalgias, low-
grade fever, and fatigue. Untreated infections
typically last for 10-12 weeks
and may follow a relapsing
course. Infections, especially
in disease-endemic settings
can be asymptomatic.
Cyclospora cayetanensis life cycle
Cyclospora cayetanensis oocysts
Spherical, 7.5-10μm. Unsporulated when passed in
feces. Sporulation in the environment is temperature-dependent, taking several weeks for an infective oocyst to contain two sporocysts, each containing two sporozoites. They autofluoresce under ultraviolet
(UV) microscopy
Cyclospora cayetanensis diagnosis (2)
- Microscopy
- Molecular – qPCR for 18S rRNA, BioFire
Cystoisospora (Isospora) belli
Pathogenic intestinal coccidia with worldwide distribution, tropical and subtropical.
Cystoisospora (Isospora) belli symptoms (5)
- Acute, non-bloody
diarrhea - Abdominal pain, can
last for weeks - Malabsorption and
weight loss - Immunocompromised
diarrhea can be severe. - Eosinophilia may be
present
Cystoisospora (Isospora) belli life cycle
Cystoisospora (Isospora) belli oocysts
Ellipsoidal shape, oocysts are large (25 to 30μm). Excreted as immature oocysts
(sporoblast) and matures after excretion. A single sporoblast divides in two sporoblasts developing cyst walls,
becoming sporocysts, four
sporozoites. Autofluoresces ultraviolet (UV) microscopy (this is how the organism is diagnosed)
Sporozoa
Parasites that lack the ability to have locomotion
Microsporidia
Pathogenic intestinal coccidia, recently confirmed to have evolved from fungi- contain chitin and trehalose & similar
gene organization as fungi, also can detect using calcofluor white. They are unicellular, obligate intracellular parasites. Spores are 1.5 to 5um width, 2 to 7um length. Intestinal microsporidiosis is found in 30-50% of AIDS patients with chronic diarrhea. Domestic and wild animals are naturally
infected- swine, primates, cattle, cats, dogs. Characterization of geographic location and problematic genera is ongoing
Why are Microsporidia medically important?
They produce resistant spores- have a unique organelle, polar tube or polar filament. Ultra structure inside the spore, coiled
How many Microsporidia species are there?
1400 species are classified in 200 genera infecting vertebrates and invertebrates. 15 microsporidian species that have been identified as human pathogens
Microsporidia pathogens (4)
- Enterocytozoon bieneusi – small intestine, biliary tree
- Encephalitozoon cuniculi, hellem, intestinalis – systemic, eyes, small intestine
- Less frequent Anncaliia algerae, connori, vesicularum – eyes, muscle, systemic
- Microsporidium - eye
Microsporidia risk factors and symptoms
Diarrhea is most common - Enterocytozoon bieneusi-associated. Observed in severely immunocompromised persons, particularly among persons with AIDS. Identification of isolates causing infection in the immunocompetent
Balamuthia mandrillaris
Causes Granulomatous amebic encephalitis (GAE)- rare BUT fatal (90% rate). Transmitted by contaminated soil (free-living trophs) entering cuts, wounds, skin abrasions, and inhaled dust. Some reports of water contamination. Enters blood stream traveling to brain and infects the immunocompetent and immunocompromised
Granulomatous amebic encephalitis (GAE) symptoms (2)
Mild but becoming severe of weeks to months:
1. Fever, headache, vomiting, lethargy
2. Mental status changes, seizures, paralysis, difficulty speaking, walking
Granulomatous amebic encephalitis (GAE) diagnosis (4)
Most commonly occurs upon autopsy, need tissue biopsy
1. Trophozoites (12-60um) in brain, cysts (13-30um)
2. IFA for the isolate
3. Serology from serum
4. PCR of biopsied tissue
Balamuthia mandrillaris life cycle
