M- Protozoal Infections of the Gut Flashcards
What are the most common protozoa associated with complicated infections?
- Entamoeba histolytical
- Giardia lamblia
- Balantidium Coli
- Microsporidia
- Cystosospora belli
- Dientameoba fragilis
What do forms does E. histolytica exist in?
Which is the infective form?
Describe the structure of each.
- Cysts- ***infective form. The cyst is 12-15microns, spherical with a halo, and can have up to 4 nuclei with central karysome and fine, uniformly distributed peripheral chromatin
- Trophozoite- 15 to 20 microns. It has a single nucleus with central karysome and uniformly distributed chromatin.
How can E. histolytica be differentiated from E. dispar?
How can histolytica be differentiated from Entamoeba coli?
In trophozoite form, E. histolytica can ingest RBCs and dispar cannot.
In cyst form, E. histolytica has 4 or fewer nuclei and E. coli can have up to 8
What is the clinical presentation of the patient has :
- luminal amebiasis
- intestinal amebiasis
- extraintestinal amebiasis
Luminal = asymptomatic
Intestinal (primary illness) =
- dysentery
- colitis
- appendicitis
- toxic megacolon
- ameboma (mass lesion or colonic wall thickening)
Extraintestinal =
- liver abscesses
- pericardial amebiasis
- pleuropulmonary amebiasis
- cerebral amebiasis
A patient presents with a history of weeks of abdominal pain, diarrhea and bloody stool. Due to the gradual onset, the patient has lost weight and seems to be volume depleted.
What is the likely protozoal cause? What would be the most serious manifestation associated with this?
It is likely to be E. histolytica causing :
Amebic colitis.
The most serious manifestation of primary disease is fulminant, necrotizing colitis
How does the presentation of amebic colitis and amebic liver abscess differ in terms of fever?
Amebic colitis is RARELY associated with fever.
Amebic liver abscess is associated with a long duration fever (1-2 wks)
What is the natural reservoir for entamoeba?
humans
What is the infectious part of E. histolytica life cyle?
Cyst:
Cysts are passed in feces and are able to live in the environment for wks because of their wall protection.
Ingestion of mature cyst in fecally contaminated water and food is the infectious step
What is the pathogenesis of E. histolytica?
What is the infectious form?
Where does the organism reside in the body?
How do they replicate?
- Ingestion of cysts in fecally contaminated H20 or food
- Cysts go to small intestine where they go through excystation to trophozoites
- Trophozoites go to large intestine and adhere to intestinal walls via lectin-binding receptors.
- Trophozoites multiply via binary fission –> cysts
- Cysts are released in feces to start the cycle again
What virulence factors allow e. histolytica trophozoites to invade intestinal mucosa?
- cytotoxins- lyse colonic epithelial cells AND lyse PMNs which release hydrolytic enzymes that further damage colonic mucosa
- cysteine proteinase- degrades collagen and elastin
Trophozoites feed on epithelium, RBC, neutrophils, monocytes, lymphocytes etc leading to:
amebic colitis
You are examining a lesion in the colon and note non-specific colitis with inflammation and flask-shaped ulcers. What protozoa are you likely to see?
E. histolytica
What is the lab diagnosis for E. histolytica? How is it differentiated from E. dispar and E. moshkovskii?
Ova and Parasite examination of the stool
Light microscopy can differentiate E.histolytica from the others because of erythrophagocytosis - it is the only entamoeba that ingests RBC
What is the only other intestinal parasite in the entamoeba family besides E. histolytica that can cause diarrhea?
Dientamoeba fragilis
What is the presence of nonpathogenic amebas in the stool of a patient strongly indicative of?
- exposure to poor sanitation/fecal contamination
- possible exposure to E. histolytica
- pre-AIDs immunodeficient state
Why are anti-motility drugs NOT recommended for patients with dysentery?
It creates the possibility of an invasive pathogen