Protozoan Parasites

Question 1

Trophozoite v. cyst forms of intestinal protozoa: which cause disease in host and which transmit the infection?

Answer 1

Trophozoite - causes disease, replicates, motile

Cyst - infective following ingestion, does not replicate, resists environmental stresses, lack motility

Question 2

Which of the pathogenic intestinal protozoa inhabit the colon?

Answer 2

Entamoeba histolytic

Question 3

What do Giardia and the Coccidia (Cryptosporidium, Cyclospora, Isospora) have in common?

Answer 3

Inhabit small bowel

Cause watery diarrhea, dysentery

Question 4

How are intestinal protozoa detected?

Answer 4

Microscopic examination of stool

Antigen detection assays, nucleic acid probes, PCR based assays in developed countries

Question 5

What are the two species of Entamoeba and which is pathogenic (invasive)?

Answer 5

Entamoeba histolytica (invasive) and Entamoeba dispar (non-invasive)

Question 6

What is the life cycle of Entamoeba histolytica?

Answer 6

• Mature cyst ingested
• Excystation to trophozoite form in colon, colonizes
• Can invade outside lumen
• Excrete cysts

Question 7

What is the name for the disorder caused by Entamoeba histolytica?

Answer 7

Amebiasis

Question 8

How can you differentiate Entamoeba histolytica from dispar histologically?

Answer 8

Histolytica ingests red blood cells and you can see it in trophozoite form on slide

Question 9

How does Entamoeba histolytica invade the colonic wall?

Answer 9

• 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

Question 10

What is the characteristic intestinal lesions caused by amebae?

Answer 10

Flask-shaped ulcer

Question 11

Which of the intestinal parasites presents with blood in the stool?

Answer 11

Entamoeba histolytica

Question 12

What is an amoeboma?

Answer 12

Ameba perforate wall of colon and cause large inflammatory mass with fibrous granulation tissue
Resembles a tumor so called amoeboma

Question 13

How do most people with E. histolytica infection present?

Answer 13

Asymptomatic cyst passer

Question 14

What is a significant complication of E. histolytica infection?

Answer 14

Hepatic abscess

Could rupture and spread to lung, pericardium

Question 15

How is amebiasis diagnosed?

Answer 15

Intestinal disease - stool microscopy, stool antigen detection, PCR
Liver abscess - ultrasound, CT, serology, needle aspirate (anchovy paste abscess fluid)

Question 16

What is the treatment for an asymptomatic cyst carrier of E. histolytica?

Answer 16

Luminal agent

• Diloxanide furoate
• Paromomycin
• Iodoquinol

Question 17

What is the treatment for someone with invasive disease due to E. histolytica?

Answer 17

Metronidazole AND a luminal agent

Question 18

What organism causes Giardia?

Answer 18

Giardia intestinalis (lamblia, duodenalis)

Question 19

What is the mode of transmission of E. histolytica?

Answer 19

Fecal-oral, but usually from ingesting contaminated water or food

Question 20

What is the mode of transmission of Giardia?

Answer 20

Person to person, or water-borne/food-borne outbreak

Question 21

What are clinical features of Giardiasis?

Answer 21

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

Question 22

How is giardiasis diagnosed?

Answer 22

Stool microscopic examination, tests for stool antigen

Question 23

Treatment for Giardiasis?

Answer 23

Metronidazole, tinidazole

Paromomycin

Question 24

How can you differentiated Cryptosporidium from Cyclospora microscopically?

Answer 24

Cyclospora autofluoresces under UV light

Question 25

What is the life cycle of Cryptosporidium?

Answer 25

- Cyst is ingested - Excystation in small bowel - Replicates intracellularly but extracytoplasmically (creates own environment in tip of cells of brush border) - Cysts excreted

Question 26

Is there an animal host of cryptosporidium?

Answer 26

NO, disease only in human

Question 27

What is the mode of transmission of cryptosporidium?

Answer 27

Fecal-oral route | Usually from treated water (recreational pools, parks, sometimes drinking water, not streams/ponds)

Question 28

Why can't an immunocompomised host clear cryptosporidium?

Answer 28

Since organism replicates intracellularly, requires cellular immunity to interrupt replication

Question 29

What is the clinical presentation of cryptosporidium in an immunocompetent host?

Answer 29

Watery diarrhea | Less common: cramps, nausea, anorexia, fever

Question 30

What is the clinical presentation of cryptosporidium in an immunocompromised host?

Answer 30

Voluminous watery diarrhea, up to 15 bowel movements a day and 10 liter fluid loss

Question 31

How is cryptosporidium diagnosed?

Answer 31

Fluorescent antibody test Modified acid-fast stain Giemsa stain

Question 32

What is the treatment of cryptosporidium in immunocompetent host?

Answer 32

Supportive therapy | Nitazoxanide (not usually necessary)

Question 33

What is the treatment of cryptosporidium in an immunocompromised host?

Answer 33

Best treatment = reversal of immune suppression with ART | Can try nitazoxanide, paromomycin, azithromycin

Question 34

Can chlorine get rid of cryptosporidium in water?

Answer 34

NO

Question 35

What is unique about the morphology of Trichomonas vaginalis?

Answer 35

Only trophozoite form, no cysts

Question 36

What is the mode of transmission of Trichomonas vaginalis?

Answer 36

Sexually transmitted

Question 37

What is the common clinical presentation of Trichomonas vaginalis?

Answer 37

Women: vaginal discharge, vulvovaginal soreness, dysuria, can be asymptomatic Men: asymptomatic or mild urethral discharge

Question 38

How does Trichomonas vaginalis increase risk for HIV?

Answer 38

- 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

Question 39

How is Trichomonas vaginalis diagnosed?

Answer 39

Wet mount microscopy Cultures RNA probe

Question 40

Treatment for Trichomonas vaginalis

Answer 40

Metronidazole or tinidazole (for both partners)

Question 41

What is the mode of transmission of Cyclospora?

Answer 41

Fecal-oral | Contaminated water and food (basil, raspberries) outbreaks

Question 42

What is the life cycle of cyclospora?

Answer 42

Ingest oocyst Sporozoites reside in epithelial cells of small bowel Excrete oocysts

Question 43

What is the clinical presentation of cyclospora infection?

Answer 43

Sudden onset Fever, cramping Watery diarrhea Can last weeks if untreated

Question 44

How is cyclospora diagnosed?

Answer 44

Stool specimen microscopy (acid fast or safranin stain) | PCR for parasite DNA

Question 45

Treatment for cyclospora

Answer 45

TMP-SMX