Giardia lamblia

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

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II. Epidemiology

  1. Most common Parasitic Infection in world (200 million infected per year)
  2. Most common Waterborne Illness in United States
    1. Cases reported per year in U.S.: 15,000 to 20,000 (esp. in children, true Incidence may be >1 million)
  3. Childhood Incidence in U.S.: 10% (at some point during childhood, esp. age <5 years)
  4. 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: Infectious Cyst transmitted via fecal-oral route
      1. Cyst is highly infectious and resistant to harsh conditions (including chlorinated water)
      2. May remain viable for months in moist environment
      3. Cyst develops into motile trophozoites in acid Stomach
    2. Stage 2: Disease-causing trophozoite
      1. Trophozoites attach to wall of Small Intestine, typically the duodenum
      2. Trophozoites multiply and some transform into cysts in the colon
      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 or poor hygiene
  2. Close contact with source case
    1. Daycare outbreaks are common
  3. Sexually-transmitted infection (oral-anal sex)
  4. Water supply from shallow well (<7.5 meters or 25 feet)
  5. Wilderness travel with ingestion of contaminated, unfiltered water
    1. See Waterborne Illness
  6. Immunocompromised
  7. Exposure to infected animals (Zoonoses)
    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 for a 5 to 25 day Incubation Period after exposure
    2. Diarrhea illness persists 1-3 weeks
    3. Diarrhea may persist with intermittent exacerbations
      1. Common infectious cause of Chronic Diarrhea (>30 days)
      2. Waxing and waning course over months
  3. Characteristics
    1. Diarrhea to loose stools without blood or mucus
    2. Steatorrhea (greasy, fatty stools)
    3. Foul smelling stools
    4. Abdominal Bloating, Belching or Flatulence
    5. Abdominal Pain or cramping
    6. Malabsorption
    7. Anorexia (Weight loss may be significant to 11 kg or 25 lb)
      1. May present as Failure to Thrive in Children
  4. Less Common findings
    1. Nausea or Vomiting
    2. Constipation
    3. Dehydration
    4. Fever suggests other diagnosis
    5. Urticaria

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 with 3 samples)
      1. Test Sensitivity is as low as 50% with a single sample
    3. Recommended even if stool Antigen testing done
      1. Identifies other concurrent Parasitic Infections
  2. Stool Giardia Antigen, PCR or DFA testing (preferred)
    1. Test Sensitivity: >90%
    2. Test Specificity: >90%
    3. Aziz (2001) Clin Lab Sci 14(3): 150-4 [PubMed]
  3. Findings suggestive of other diagnosis
    1. Fecal Leukocytes are not seen in Giardiasis
    2. Leukocytosis and Eosinophilia are not seen in Giardiasis

VIII. Differential Diagnosis

  1. See Infectious Diarrhea
  2. See Unintentional Weight Loss
  3. Irritable Bowel Syndrome
    1. Giardia is often misdiagnosed as Irritable Bowel Syndrome initially in U.S.

IX. Management: Primary Regimens

  1. See Acute Diarrhea for non-specific supportive care (rehydration, Electrolyte evaluation)
  2. Adults: Primary options (choose one)
    1. Tinidazole
      1. Take 2 grams orally for 1 dose
      2. Preferred, with best efficacy (>90% cure rate in children and adults)
    2. Nitazoxanide (Alinia)
      1. Take 500 mg orally twice daily for 3 days
  3. Adults: Alternative options
    1. Metronidazole (Flagyl)
      1. Take 500 mg orally twice daily for 5 to 7 days OR
      2. Take 250 mg orally three times daily for 5 to 7 days
    2. Furazolidone 100 mg orally four times daily for 7 days
    3. Albendazole 400 mg orally daily with food for 5 days
  4. Adults: 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
  5. Adults: 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
  6. Child
    1. Metronidazole (Flagyl)
      1. Dose: 5 to 10 mg/kg/dose (max 250 mg) orally three times daily for 7 days
      2. Bitter and not well tolerated by children
      3. Preferred for infants under age 1 year
      4. Cure rates 80% in children
    2. Nitazoxanide (Alinia)
      1. Age 1 to 3 years: 100 mg orally twice daily for 3 days
      2. Age 4 to 11 years: 200 mg orally twice daily for 3 days
      3. Cure rates 85% in children
    3. Tindazole
      1. Age >=3 years: 50 mg/kg (max: 2 grams) for one dose
  7. 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. Metronidazole (Flagyl) has also been used in pregnancy
  8. Asymptomatic carrier AND immunocompetent (without Immunocompromised exposures)
    1. Developed country: Treat per above guidelines
    2. Undeveloped country: Treatment not recommended (High risk of reinfection)

X. 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

XI. Prevention

  1. See Prevention of Foodborne Illness
  2. See Prevention of Waterborne Illness
  3. Avoid swimming in pool for 3 weeks after Giardia resolution
    1. 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 for 10 minutes
      1. Some guidelines recommend boiling for 10 minutes
    4. Water microfiltration (1 micron pore)
  5. Ensure adequate sanitation system of water treatment
  6. Prevention in daycare settings
    1. Dispose of diapers properly
    2. Frequent and thorough Hand Washing

XII. Complications

  1. Vitamin D Deficiency
  2. Failure to Thrive, Growth Delay or Unintentional Weight Loss
  3. Pancreatobiliary spread (rare)
  4. Lactose Intolerance
    1. Avoid dairy products for 1 month after treatment to avoid confusion regarding persistent or recurrent symptom cause
  5. Treatment failure or reinfection
    1. High risk of reinfection in undeveloped countries or unreliable water source
    2. No test for cure needed after treatment if asymptomatic
    3. Recurrent symptoms should prompt retesting and repeat treatment if positive

XIII. References

  1. Gilbert (2016) Sanford Guide, accessed on IOS, 9/12/2016
  2. Stannard, Rogers and Kernen (2023) Crit Dec Emerg Med 37(7): 24-9
  3. Kucik (2004) Am Fam Physician 69:1161-8 [PubMed]
  4. Nash (2001) Pediatr Infect Dis J 20:193-6 [PubMed]
  5. Perkins (2017) Am Fam Physician 95(9):554-60 [PubMed]
  6. Pyzocha (2023) Am Fam Physician 108(5): 487-93 [PubMed]

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