Giardia lamblia

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

1. See Also
   1. Diarrhea
   2. Infectious Diarrhea
2. 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.
3. Pathophysiology
   1. Characteristics
      1. Pear-shaped flagellated protozoan
   2. Low inoculum: <10-25 cysts
   3. Causative Organisms
      1. Giardia lamblia
      2. Giardia intestinalis
   4. Transmission: Fecal-oral
   5. 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
4. 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
5. Symptoms
   1. Timing
      1. Onset delayed 5-25 days after exposure
      2. Diarrhea illness persists 1-3 weeks
      3. Diarrhea may persist with intermittent exacerbations
   2. Characteristics
      1. Diarrhea without blood or mucus
      2. Steatorrhea
      3. Flatulence
      4. Abdominal Pain
      5. Belching
      6. Malabsorption
      7. Weight loss may be significant
   3. Less Common findings
      1. Nausea or Vomiting
      2. Dehydration
      3. Fever suggests other diagnosis
6. Labs
   1. Stool Ova and Parasite
      1. Low sensitivity for Giardia cysts
      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
7. Management
   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 twice daily for 5 days
   3. 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
   4. Refractory cases: Option 1
      1. Metronidazole (Flagyl) 750 mg orally three times daily for 3 weeks AND
      2. Quinacrine 100 mg orally three times daily for 3 weeks
   5. Refractory cases: Option 2
      1. Furazolidone 100 mg orally four times daily for 7 days
   6. Refractory cases: Option 3
      1. Nitazoxanide 500 mg orally twice daily for 3 days or
   7. Asymptomatic carrier
      1. Developed country: Treat per above guidelines
      2. Undeveloped country: Treatment not recommended (High risk of reinfection)
   8. 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
8. Management: Miscellanous agents
   1. Albendazole
      1. Adults or children: 400 mg PO qd 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
9. Management: Resistant cases
   1. Consider Flagyl with Quinacrine for 3 week course
   2. Consider Albendazole (not FDA approved)
10. Prevention
    1. See Prevention of Foodborne Illness
    2. See Prevention of Waterborne Illness
    3. 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
    4. Ensure adequate sanitation system of water treatment
    5. Prevention in daycare settings
       1. Dispose of diapers properly
       2. Frequent and thorough hand washing
11. References
    1. Gilbert (2011) Sanford Guide, p. 129
    2. Kucik (2004) Am Fam Physician 69:1161-8
    3. Nash (2001) Pediatr Infect Dis J 20:193-6