GI Infections: Protozoa

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

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