Balantidium coli

Introduction

Largest protozoan to infect humans.

Epidemiology

• acquired by ingestion of infective cysts via contaminated food or water
• organisms migrate to the colon where the develop into trophozoites
• trophozoites comsume bacteria & replicate by binary fission & conjugation
• human infection is rare in USA & generally acquired from hogs
• hogs are commonly infected

Pathology

• trophozoites reside primarily in lumen of colon, but may penetrate the intestinal mucosa & cause ulcers, colitis

Clinical manifestations

• most cases asymptomatic
• bloody diarrhea &/or mucoid diarrhea
• nausea/vomiting, dehydration
• abdominal pain
• anorexia, weight loss
• fever

Laboratory

• diagnosis is made by recovery of trophozoites or cysts in feces (wet mount)
• trophozoites
  • measure 40-200 um (generally 50-100 um)
  • uniformly covered with cilia
  • large macronucleus (easily seen with stains) & smaller micronucleus (generally not visualized)
  • numerous vacuoles in cytoplasm
• cysts
  • rounded, measuring 50-70 um
  • cilia may be seen with younger cysts
  • nuclei similar to trophozoites
• stool specimens contaminated with stagnant water may contain free-living ciliates distinguishable from B coli by differences in ciliary patterns

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Management

• electrolyte replacement
• tetracycline 500 mg PO QID is effective
• metronidazole or iodoquinol are alternatives

More general terms

• Balantidium

Additional terms

• trophozoite