Updated: 12/12/2019

GI Infections: Protozoa

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Snapshot
  • A 26-year-old woman presents to the emergency room for large amounts of watery, nonbloody diarrhea, abdominal cramping, and lots of flatulence. She was trying to hydrate with water and sports drinks; however, she started feeling lightheaded and was brought to the hospital for treatment. She recently did a 5-day hike in Patagonia in South America. On physical exam, she demonstrated signs of dehydration but otherwise has no significant findings. Stool studies are sent and return with cysts on microscopy. (Giardia lamblia infection)
Introduction
  • Protozoa
    • single-celled eukaryotes, often parasitic, that feed on organic tissues
Infections of Protozoa
Central Nervous System
Gastrointestinal
Visceral Infections
Hematologic Infections Sexually Transmitted Diseases
  • Toxoplasma gondii
  • Naegleria fowleri
  • Trypanosoma brucei
  • Acanthamoeba
  • Giardia lamblia
  • Entamoeba histolytica
  • Cryptosporidium
  • Trypanosoma cruzi
  • Leishmania donovani
  • Plasmodium
  • Babesia
  • Trichomonas vaginalis

Giardia lamblia
  • Introduction 
    • clinical syndrome
      • giardiasis
    • demographics
      • very common, especially in South America and Southeast Asia
    • transmission
      • ingestion of cysts in contaminated water
    • pathogenesis
      • only requires a few cysts to cause giardiasis
    • risk factors
      • camping and hiking
      • poor sanitation
      • IgA deficiencies
        • Burton agammaglobulinemia
        • common variable immunodeficiency
        • selective IgA deficiency
  • Presentation
    • 1-2 weeks after exposure
    • abdominal pain and bloating
    • flatulence
    • large-volume, watery, foul-smelling, fatty diarrhea
  • Studies
    • stool microscopy
      • microscopy multinucleated trophozoites
      • cysts
    • stool antigen test
  • Treatment
    • metronidazole
      • first-line
      • if asymptomatic, patients may not need treatment unless they are at risk for severe disease (immunosuppression)
    • paromomycin
      • pregnant women
Entamoeba histolytica
  • Introduction
    • clinical syndrome
      • amebiasis
      • hepatic abscess
    • demographics
      • tropical areas
    • transmission
      • ingestion of cysts in contaminated water
      • fecal-oral
    • risk factors
      • poor sanitation
      • pregnancy
      • immunosuppression
  • Presentation
    • fever
    • bloody or watery diarrhea
    • right upper quadrant pain
      • should raise suspicion for liver abscess    
  • Imaging
    • abdominal computed tomography (CT) or ultrasound
      • liver abscess
  • Studies
    • stool antigen test
    • stool detection of DNA with polymerase chain reaction (PCR)
    • stool microscopy
      • trophozoites with ingested red blood cells in the cytoplasm
      • cysts with multiple nuclei
    • histology
      • flask-shaped lesions
  • Treatment
    • metronidazole
      • symptomatic patients
    • paromomycin or iodoquinol
      • asymptomatic patients with cysts detected in stool
    • needle aspiration or percutaneous drainage of abscess
      • liver abscess often has an “anchovy paste” or red-brown exudate
Cryptosporidium
  • Introduction
    • clinical syndrome
      • cryptosporidiosis
    • transmission
      • ingestion of oocysts in contaminated water
      • fecal-oral
    • risk factors
      • immunosuppression
      • HIV/AIDS
    • Prevention
      • filter all drinking water
  • Presentation
    • immunosuppressed patients
      • severe and prolonged nonbloody diarrhea
      • may be fatty
      • weight loss
    • immunocompetent patients
      • mild watery diarrhea
  • Studies
    • acid-fast stain
      • oocysts
    • detection of antigen
  • Treatment
    • nitazoxanide
      • immunocompetent patients

 

Microsporidium
  • Introduction
    • clinical syndrome
      • microsporidiosis
    • transmission
      • fecal-oral
    • risk factors
      • immunosuppression
      • HIV/AIDs
      • organ transplant
  • Presentation
    • weight loss
    • nonbloody and watery diarrhea
    • nausea and vomiting
    • can also cause keratoconjunctivitis
  • Studies
    • stool detection of DNA with polymerase chain reaction (PCR)
    • stool microscopy with trichrome stain
      • ovoid spores with bright red walls
      • gram-positive
  • Treatment
    • albendazole
      • first-line
    • topical fumagillin
      • keratoconjunctivitis
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Questions (9)
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(M1.MC.17.4753) A 26-year-old male presents to his primary care physician complaining of diarrhea. He recently returned from a two-week hike in the Peruvian Andes mountains, during which time he ate undercooked chicken and beef. Since returning, he has experienced frequent bloating, flatulence, and several foul-smelling watery stools per day. He has recently noticed blood on the toilet paper after wiping. His past medical history is notable for asthma. He takes albuterol and low-dose budesonide. His temperature is 100°F (37.8°C), blood pressure is 120/70 mmHg, pulse is 90/min, and respirations are 20/min. A stool sample is shown in Figure A. What is the most appropriate treatment for this patient? Tested Concept

QID: 108889
FIGURES:
1

Metronidazole

85%

(216/253)

2

Ciprofloxacin

4%

(11/253)

3

Amipicillin

3%

(7/253)

4

Vancomyin

4%

(11/253)

5

Sulfasalazine

1%

(2/253)

M 3 C

Select Answer to see Preferred Response

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(M1.MC.15.2) A 19-year-old male recently returned home from a camping trip. He is planning on heading back to college but is worried that he may have a parasitic infection after drinking unfiltered stream water on his trip. He sets up an appointment with his primary care physician. The patient denies any diarrhea, constipation, bloating, or flatulence. He is adamant about having a fecal exam, so the primary care physician obliges. His stool sample is shown in Figure A. What is the most appropriate next step in this patient's care? Tested Concept

QID: 102943
FIGURES:
1

Treatment with metronidazole to prevent future symptoms, as he is infected with giardia lamblia.

46%

(31/67)

2

Treatment with azithromycin because he is infected with cryptosporidium.

4%

(3/67)

3

No treatment, as he is not currently infected with any organisms.

3%

(2/67)

4

No treatment because he is not experiencing any symptoms.

37%

(25/67)

5

No treatment because there is no effective treatment for his current pathologic state.

7%

(5/67)

M 3 D

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(M1.MC.15.74) A 17-year-old male returns from a camping trip. He complains of abdominal bloating and flatulence. On further review, he reports foul-smelling diarrhea, which is difficult to flush. The results of staining a stool specimen with iodine are shown in Figure A.

Which of the following treatment options is most appropriate?
Tested Concept

QID: 106700
FIGURES:
1

Penicillin

1%

(4/270)

2

Azithromycin

2%

(6/270)

3

Metronidazole

89%

(239/270)

4

Trimethoprim-sulfamethoxazole

5%

(14/270)

5

Ribavirin

0%

(1/270)

M 3 D

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(M1.MC.15.74) A 5 year-old-boy with a history of severe allergies and recurrent sinusitis presents with foul-smelling, fatty diarrhea. He is at the 50th percentile for height and weight. The boy's mother reports that he has had several such episodes of diarrhea over the years. He does not have any known history of fungal infections or severe viral infections. Which of the following is the most likely underlying cause of this boy's presentation? Tested Concept

QID: 106684
1

Thymic aplasia

2%

(1/59)

2

Hyper IgE syndrome

14%

(8/59)

3

Severe combined immune deficiency

8%

(5/59)

4

Wiskott-Aldrich Syndrome

3%

(2/59)

5

IgA deficiency

69%

(41/59)

M 1 B

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Topic COMMENTS (13)
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