Giardia lamblia

Aka: Giardia lamblia, Giardia intestinalis, G. lamblia, Giardia, Beaver Fever, Backpacker's Diarrhea

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II. Epidemiology

  1. Most common Parasitic Infection in world
  2. Most common Waterborne Illness in United States
  3. Incidence: 2.5 million cases per year in U.S.
  4. Childhood Incidence in U.S.: 10% (at some point during childhood)
  5. Summer rates of Giardia infection are double that of other times of year

III. Pathophysiology

  1. Characteristics
    1. Pear-shaped flagellated protozoan
  2. Low inoculum: <10-25 cysts (even a single oocyst)
  3. High concentration of shedded oocysts (100 million daily)
  4. Causative Organisms
    1. Giardia lamblia
    2. Giardia intestinalis
  5. Transmission: Fecal-oral
  6. Life Cycle
    1. Stage 1: Cyst transmitted via fecal-oral route
      1. May remain viable for months in moist environment
      2. Cyst develops into 2 trophozoites in acid Stomach
    2. Stage 2: Disease-causing trophozoite
      1. Trophozoites attach to wall of Small Intestine
      2. Trophozoites multiply and some transform to cysts
      3. Cysts are passed with feces to restart cycle

IV. Precautions

  1. As with Cryptosporidium, Giardia oocysts can survive in chlorinated pools and hot tubs

V. Risk Factors

  1. Poor sanitation
  2. Close contact with source case
    1. Daycare outbreaks are common
  3. Sexually-transmitted infection (oral-anal sex)
  4. Wilderness travel with ingestion of contaminated water
  5. Exposure to infected animals (zoonosis)
    1. Beaver
    2. Cattle
    3. Dogs
    4. Rodents
    5. Bighorn Sheep

VI. Symptoms

  1. Asymptomatic in 50% of those infected
  2. Timing
    1. Onset delayed 5-25 days after exposure
    2. Diarrhea illness persists 1-3 weeks
    3. Diarrhea may persist with intermittent exacerbations
  3. Characteristics
    1. Diarrhea without blood or mucus
    2. Steatorrhea
    3. Flatulence
    4. Abdominal Pain
    5. Belching
    6. Malabsorption
    7. Weight loss may be significant
  4. Less Common findings
    1. Nausea or Vomiting
    2. Dehydration
    3. Fever suggests other diagnosis

VII. Labs

  1. Stool Ova and Parasite
    1. Low sensitivity for Giardia cysts (oocysts are excreted intermittently)
    2. Requires three loose stool samples (85-90% sensitive)
    3. Recommended even if stool Antigen testing done
      1. Identifies other concurrent Parasitic Infections
  2. Stool Giardia Antigen testing
    1. Test Sensitivity: >90%
    2. Test Specificity: >95%
  3. Findings suggestive of other diagnosis
    1. Fecal Leukocytes not seen in Giardiasis
    2. Leukocytosis or Eosinophilia not seen in Giardiasis

VIII. Management: Primary Regimens

  1. Primary options
    1. Nitazoxanide 500 mg orally twice daily for 3 days or
    2. Tinidazole 2 grams orally for 1 dose (expensive)
  2. Alternative options
    1. Metronidazole 250 mg orally three times daily for 5-7 days
    2. Furazolidone 100 mg orally four times daily for 7 days
    3. Albendazole 400 mg orally daily with food for 5 days
  3. Refractory cases or immunodeficient: Option 1
    1. Metronidazole (Flagyl) 750 mg orally three times daily for 3 weeks AND
    2. Add ONE of the following
      1. Quinacrine 100 mg orally three times daily for 3 weeks OR
      2. Paromomycin: 10 mg/kg three times daily for 3 weeks
  4. Refractory cases or immunodeficient: Option 2
    1. Metronidazole (Flagyl) 250 mg orally three times daily for 5 days AND
    2. Albendazole 400 mg orally daily with food for 5 days
  5. Child
    1. Flagyl is bitter and not well tolerated by children
    2. Dose: 5 mg/kg/dose (max 250 mg) PO tid for 7 days
  6. Pregnancy
    1. Mild cases: Consider delaying until post-delivery
    2. Moderate to severe cases
      1. Paromycin 25-35 mg/kg/day in 3 divided doses orally for 5-10 days
      2. Flagyl has also been used in pregnancy
  7. Asymptomatic carrier
    1. Developed country: Treat per above guidelines
    2. Undeveloped country: Treatment not recommended (High risk of reinfection)

IX. Management: Miscellanous agents

  1. Albendazole
    1. Adults or children: 400 mg orally daily for 5 days
    2. Not FDA approved for Giardiasis
  2. Quinacrine (70-95% effective) - not available in U.S.
    1. Adults: 100 mg PO tid for 5 days
    2. Child: 0.7 mg/kg/dose (max 100/day) PO tid for 7 days
  3. Furazolidone (Furoxone)
    1. More tolerable taste for young children
    2. Less effective in older children than other agents
    3. Risk of Hemolysis with G6PD Deficiency
    4. Child: 1.25 mg/kg/dose (max 100 mg) PO qid for 7 days
  4. Paromomycin (Humatin)
    1. Oral Aminoglycoside with poor systemic absorption
    2. Consider when desire no absorption (e.g. pregnancy)
    3. Adult: 500 mg PO qid for 7-10 days
    4. Child: 25-35 mg/kg/day divided tid for 7 days

X. Prevention

  1. See Prevention of Foodborne Illness
  2. See Prevention of Waterborne Illness
  3. Avoid swimming in pool for 3 weeks after resolution (asymptomatic shedding persists for 1-3 weeks after resolution)
  4. Water Disinfection
    1. Use only bottled water in endemic areas if possible
    2. Intermediate halogen resistance to (Iodine, Fluorine)
      1. Use halogen for longer time before drinking
      2. Use Iodine purification tablets for >8 hours
    3. Boil water for 1 minute or heat to 158 F x10 minutes
    4. Water Filtration
  5. Ensure adequate sanitation system of water treatment
  6. Prevention in daycare settings
    1. Dispose of diapers properly
    2. Frequent and thorough Hand Washing

XI. References

  1. Gilbert (2016) Sanford Guide, accessed on IOS, 9/12/2016
  2. Kucik (2004) Am Fam Physician 69:1161-8 [PubMed]
  3. Nash (2001) Pediatr Infect Dis J 20:193-6 [PubMed]
  4. Perkins (2017) Am Fam Physician 95(9):554-60 [PubMed]

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