Protozoan Parasites Flashcards
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?
Entamoeba histolytic
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?
Amebiasis
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?
Flask-shaped ulcer
Which of the intestinal parasites presents with blood in the stool?
Entamoeba histolytica
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?
Hepatic abscess
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?
Luminal agent
- Diloxanide furoate
- Paromomycin
- Iodoquinol
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?
Metronidazole, tinidazole
Paromomycin
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?
Fecal-oral route
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?
Watery diarrhea
Less common: cramps, nausea, anorexia, fever
What is the clinical presentation of cryptosporidium in an immunocompromised host?
Voluminous watery diarrhea, up to 15 bowel movements a day and 10 liter fluid loss
How is cryptosporidium diagnosed?
Fluorescent antibody test
Modified acid-fast stain
Giemsa stain
What is the treatment of cryptosporidium in immunocompetent host?
Supportive therapy
Nitazoxanide (not usually necessary)
What is the treatment of cryptosporidium in an immunocompromised host?
Best treatment = reversal of immune suppression with ART
Can try nitazoxanide, paromomycin, azithromycin
Can chlorine get rid of cryptosporidium in water?
NO
What is unique about the morphology of Trichomonas vaginalis?
Only trophozoite form, no cysts
What is the mode of transmission of Trichomonas vaginalis?
Sexually transmitted
What is the common clinical presentation of Trichomonas vaginalis?
Women: vaginal discharge, vulvovaginal soreness, dysuria, can be asymptomatic
Men: asymptomatic or mild urethral discharge
How does Trichomonas vaginalis increase risk for HIV?
- Weakens integrity of epithelial barrier
- Decreases innate immunity and normal epithelial defenses
- Disrupts lactobacilli-dominated vaginal microbiome
- In males infected with HIV, co-infection with trichomoniasis causes 6x increase in HIV viral load in semen
How is Trichomonas vaginalis diagnosed?
Wet mount microscopy
Cultures
RNA probe
Treatment for Trichomonas vaginalis
Metronidazole or tinidazole (for both partners)
What is the mode of transmission of Cyclospora?
Fecal-oral
Contaminated water and food (basil, raspberries) outbreaks
What is the life cycle of cyclospora?
Ingest oocyst
Sporozoites reside in epithelial cells of small bowel
Excrete oocysts
What is the clinical presentation of cyclospora infection?
Sudden onset
Fever, cramping
Watery diarrhea
Can last weeks if untreated
How is cyclospora diagnosed?
Stool specimen microscopy (acid fast or safranin stain)
PCR for parasite DNA
Treatment for cyclospora
TMP-SMX
