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.

III. 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

IV. 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

V. 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

VI. 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

VII. 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)

VIII. 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

IX. 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

X. References

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Ontology: Giardia (C0017534)

Definition (MSH) A genus of flagellate intestinal EUKARYOTES parasitic in various vertebrates, including humans. Characteristics include the presence of four pairs of flagella arising from a complicated system of axonemes and cysts that are ellipsoidal to ovoidal in shape.
Definition (MSHCZE) Rod bičíkovců žijících v tenkém střevě savců, původce giardiázy (lambliázy). Dř. název byl Lamblia. (cit. Velký lékařský slovník online, 2013 http://lekarske.slovniky.cz/ )
Definition (NCI) A genus of parasitic protozoa that is the cause of giardiasis.
Definition (CSP) genus in the Diplomonadida order; flagellate intestinal protozoa parasitic in various vertebrates, including humans; characteristics include the presence of four pairs of flagella arising from a complicated system of axonemes and cysts that are ellipsoidal to ovoidal in shape.
Concepts Eukaryote (T204)
MSH D005872
SnomedCT 61419001
LNC LP20007-8
English Giardia, Lamblia, Lamblias, Giardias, giardia parasite, giardia, Giardia Kunstler, Genus: Giardia, Giardia (organism), lamblia, Giardia, NOS
Swedish Giardia
Czech Giardia, Lamblia
Finnish Giardia
Italian Lamblia, Giardia
Russian LIAMBLII, ZHIARDII, ЖИАРДИИ, ЛЯМБЛИИ
Polish Lamblia
Japanese Giardia属, ジアルジア, ジアルジア属, ヤツヒゲハラムシ, ランブリア, ランブリア属
Norwegian Giardia, Lamblia
Spanish Giardia (organismo), Giardia, Lamblia
French Giardia
German Giardia, Lamblien
Dutch Giardia, Lamblia
Portuguese Giardia, Lamblia

Ontology: Giardia lamblia (C0017535)

Definition (MSH) A species of parasitic EUKARYOTES that attaches itself to the intestinal mucosa and feeds on mucous secretions. The organism is roughly pear-shaped and motility is somewhat erratic, with a slow oscillation about the long axis.
Definition (MSHCZE) Lat. prvok, bičíkovec vyvolávající giardiázu (lambliázu). Trofozoit má hruškovitý tvar, dvě jádra, čtyři páry bičíků, velikost cca 5–15 a 10–20 µm. Žije na povrchu sliznice horních částí tenkého střeva. Tvoří menší (cca 8x12 µm), čtyřjaderné, značně odolné cysty, které jsou vylučovány stolicí. G. l. je kosmopolitně rozšířena, přenáší se alimentární cestou. Dřívější název Lamblia intestinalis se stále používá, i v cizině. (cit. Velký lékařský slovník online, 2013 http://lekarske.slovniky.cz/ )
Concepts Eukaryote (T204)
MSH D016829
SnomedCT 19122007, 78181009
LNC LP14122-3, MTHU033938
English Giardia intestinalis, Lamblia intestinalis, Giardia lamblias, giardia lamblia, lamblia giardia, giardia duodenalis, giardia intestinalis, Giardia duodenalis, GIARDIA LAMBLIA, Giardia intestinalis (Lambl, 1859) Kofoid & Christiansen, 1915, Gl - Giardia lamblia, Giardia intestinalis (organism), Giardia lamblia (organism), Giardia lamblia
Swedish Giardia lamblia
Czech Giardia intestinalis, Giardia lamblia, Lamblia intestinalis
Finnish Giardia lamblia
Russian LIAMBLIIA KISHECHNAIA, DZHIARDIIA KISHECHNAIA, GIARDIA LAMBLIA, ДЖИАРДИЯ КИШЕЧНАЯ, ЛЯМБЛИЯ КИШЕЧНАЯ
Italian Giardia intestinalis, Lamblia intestinalis, Giardia lamblia
Polish Giardia lamblia, Giardia intestinalis, Lamblia intestinalis
Japanese 腸鞭毛虫, ランブル鞭毛虫
Portuguese Giardia duodenalis, Giardia intestinalis, Giardia lamblia, Lamblia intestinalis
Spanish Giardia duodenalis, Giardia intestinalis (organismo), Giardia lamblia (organismo), Giardia intestinalis, Giardia lamblia, Lamblia intestinalis
Norwegian Giardia intestinalis, Lamblia intestinalis, Giardia lamblia, Giardia duodenalis
French Giardia intestinalis, Giardia lamblia, Lamblia intestinalis
German Giardia intestinalis, Giardia lamblia, Lamblia intestinalis
Dutch Giardia intestinales, Giardia lamblia, Lamblia intestinales

Ontology: Giardia lamblia antigen (C0369266)

Concepts Immunologic Factor (T129)
SnomedCT 121081002
LNC LP38239-7, MTHU004731
English Giardia lamblia Antigen, Giardia lamblia Ag, Giardia Lamblia Antigen, Giardia lamblia antigen (substance), Giardia lamblia antigen
Spanish antígeno de Giardia lamblia (sustancia), antígeno de Giardia lamblia