Flashcards in Protozoan Parasites Deck (45)
Trophozoite v. cyst forms of intestinal protozoa: which cause disease in host and which transmit the infection?
Trophozoite - causes disease, replicates, motile
Cyst - infective following ingestion, does not replicate, resists environmental stresses, lack motility
Which of the pathogenic intestinal protozoa inhabit the colon?
What do Giardia and the Coccidia (Cryptosporidium, Cyclospora, Isospora) have in common?
Inhabit small bowel
Cause watery diarrhea, dysentery
How are intestinal protozoa detected?
Microscopic examination of stool
Antigen detection assays, nucleic acid probes, PCR based assays in developed countries
What are the two species of Entamoeba and which is pathogenic (invasive)?
Entamoeba histolytica (invasive) and Entamoeba dispar (non-invasive)
What is the life cycle of Entamoeba histolytica?
- Mature cyst ingested
- Excystation to trophozoite form in colon, colonizes
- Can invade outside lumen
- Excrete cysts
What is the name for the disorder caused by Entamoeba histolytica?
How can you differentiate Entamoeba histolytica from dispar histologically?
Histolytica ingests red blood cells and you can see it in trophozoite form on slide
How does Entamoeba histolytica invade the colonic wall?
- Amoebas adhere to epithelial cells (using Gal/GalNac lectin)
- Secretes cysteine proteases to degrade the extracellular matrix
- Form pores (amebapores) in target cells that depolarizes and kills cell
What is the characteristic intestinal lesions caused by amebae?
Which of the intestinal parasites presents with blood in the stool?
What is an amoeboma?
Ameba perforate wall of colon and cause large inflammatory mass with fibrous granulation tissue
Resembles a tumor so called amoeboma
How do most people with E. histolytica infection present?
Asymptomatic cyst passer
What is a significant complication of E. histolytica infection?
Could rupture and spread to lung, pericardium
How is amebiasis diagnosed?
Intestinal disease - stool microscopy, stool antigen detection, PCR
Liver abscess - ultrasound, CT, serology, needle aspirate (anchovy paste abscess fluid)
What is the treatment for an asymptomatic cyst carrier of E. histolytica?
- Diloxanide furoate
What is the treatment for someone with invasive disease due to E. histolytica?
Metronidazole AND a luminal agent
What organism causes Giardia?
Giardia intestinalis (lamblia, duodenalis)
What is the mode of transmission of E. histolytica?
Fecal-oral, but usually from ingesting contaminated water or food
What is the mode of transmission of Giardia?
Person to person, or water-borne/food-borne outbreak
What are clinical features of Giardiasis?
Watery, foul smelling diarrhea
Abdominal distension, flatulence, cramps, anorexia
Chills, low-grade fever, weight loss
Blood and mucus not found in stool
Can be asymptomatic cyst passer
How is giardiasis diagnosed?
Stool microscopic examination, tests for stool antigen
Treatment for Giardiasis?
How can you differentiated Cryptosporidium from Cyclospora microscopically?
Cyclospora autofluoresces under UV light
What is the life cycle of Cryptosporidium?
- Cyst is ingested
- Excystation in small bowel
- Replicates intracellularly but extracytoplasmically (creates own environment in tip of cells of brush border)
- Cysts excreted
Is there an animal host of cryptosporidium?
NO, disease only in human
What is the mode of transmission of cryptosporidium?
Usually from treated water (recreational pools, parks, sometimes drinking water, not streams/ponds)
Why can't an immunocompomised host clear cryptosporidium?
Since organism replicates intracellularly, requires cellular immunity to interrupt replication
What is the clinical presentation of cryptosporidium in an immunocompetent host?
Less common: cramps, nausea, anorexia, fever