Giardia lamblia: Difference between revisions

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Giardia lamblia
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* A member of the [[Giardia species]] that causes intestinal disease ('''giardiasis''') in humans and animals
+
*A member of the [[Giardia]] that causes intestinal disease ('''giardiasis''') in humans and animals
* Also known as '''beaver fever'''
+
*Also known as '''beaver fever'''
   
== Background ==
+
==Background==
   
=== Microbiology ===
+
===Microbiology===
   
* Flagellated protozoan that infects the small bowel
+
*Flagellated protozoan that infects the small bowel
* Host specificity related to genotype ("assemblage")
+
*Host specificity related to genotype ("assemblage")
** Assemblages A & B infect humans, but also numerous non-human hosts including primates, dogs, cats, cattle, sheep, deer, rodents, horses, and beavers
+
**Assemblages A & B infect humans, but also numerous non-human hosts including primates, dogs, cats, cattle, sheep, deer, rodents, horses, and beavers
** Assemblages C & D affect dogs; E affects cattle, goats, sheep, and pigs; F affects cats; G affects rodents; and H affects marine vertebrates
+
**Assemblages C & D affect dogs; E affects cattle, goats, sheep, and pigs; F affects cats; G affects rodents; and H affects marine vertebrates
* Antigenic variation is determined by the variant-specific surface protein (VSP)
+
*Antigenic variation is determined by the variant-specific surface protein (VSP)
** Replaced every few generations
+
**Replaced every few generations
   
=== Life Cycle ===
+
===Life Cycle===
   
* A cyst is ingested via fecal-oral contamination
+
*A cyst is ingested via fecal-oral contamination
* In the small bowel, the cyst releases two trophozoites (free-living form) via excystation
+
*In the small bowel, the cyst releases two trophozoites (free-living form) via excystation
* Trophozoites multiply by binary fission
+
*Trophozoites multiply by binary fission
* When they reach the large bowel, they encyst
+
*When they reach the large bowel, they encyst
   
=== Epidemiology ===
+
===Epidemiology===
   
* Worldwide distribution
+
*Worldwide distribution
* Generally transmitted fecal-oral route (via environment), but person-to-person transmission is possible in daycares
+
*Generally transmitted fecal-oral route (via environment), but person-to-person transmission is possible in daycares
* Numerous animal reservoirs, not fully understood how important they are
+
*Numerous animal reservoirs, not fully understood how important they are
* Cysts can survive several months in cold water
+
*Cysts can survive several months in cold water
* Peak prevalence occurs in children of up to 15 to 30% in poor countries
+
*Peak prevalence occurs in children of up to 15 to 30% in poor countries
* Reinfection is common
+
*Reinfection is common
   
=== Pathophysiology ===
+
===Pathophysiology===
   
* Infected with as few as 10 to 25 cysts
+
*Infected with as few as 10 to 25 cysts
* Trophozoites colonize the upper small bowel, adhering to the mucosal enterocytes
+
*Trophozoites colonize the upper small bowel, adhering to the mucosal enterocytes
* Host response involves B- and T-cells, including production of IgM and IgG antibodies, possibly IgA antibodies as well
+
*Host response involves B- and T-cells, including production of IgM and IgG antibodies, possibly IgA antibodies as well
  +
*Causes villous atrophy, which can contribute to malabsorption
  +
*Inhibits disaccharidases, which contributes to lactose intolerance
   
== Clinical Presentation ==
+
==Clinical Manifestations==
   
* Can have '''asymptomatic cyst passage''' (5 to 15%)
+
*Can have '''asymptomatic cyst passage''' (5 to 15%)
** Can last up to 6 months in children
+
**Can last up to 6 months in children
* Most common syndrome is '''acute diarrhea''' (25 to 50%)
+
*Most common syndrome is '''acute diarrhea''' (25 to 50%)
** Incubation period 1 to 2 weeks
+
**Incubation period [[Usual incubation period::1 to 2 weeks]]
  +
**Usually presents after 7 to 10 days
** Malaise, flatulence, cramps, bloating, nausea, anorexia, vomiting, and malabsorption
+
**Malaise, flatulence, cramps, bloating, nausea, anorexia, vomiting, and malabsorption
** '''Sulfuric belching''' is classic
+
**'''Sulfuric belching''' is classic
** Fevers are uncommon but possible
+
**Fevers are uncommon but possible
* Can also cause '''chronic diarrhea'''
+
*Can also cause '''chronic diarrhea'''
** Malaise, occasional headache, diffuse abdominal and epigastric pain worse with food
 
  +
**More common in [[CVID]], [[X-linked agammaglobulinemia]], and [[AIDS]]
** May have malabsorption, often has weight loss
 
 
**Malaise, occasional headache, diffuse abdominal and epigastric pain worse with food
** Symptoms can wx and wane, with periods of remission or constipation
 
 
**May have malabsorption, often has weight loss
* '''Post-''Giardia'' syndrome''' with irritable bowel syndrome and chronic fatigue may last for years
 
 
**Symptoms can wax and wane, with periods of remission or constipation
** Can have significant malabsorption
 
 
*'''Post-''Giardia'' syndrome''' with irritable bowel syndrome and chronic fatigue may last for years
* Also, can have '''post-''Giardia'' lactose intolerance''' lasting several weeks
 
 
**Can have significant malabsorption
 
*Also, can have '''post-''Giardia'' lactose intolerance''' lasting several weeks
   
== Diagnosis ==
+
==Diagnosis==
   
* Stool microscopy
+
*Stool microscopy
** May see active trophozoites in saline wet prep
+
**May see active trophozoites in saline wet prep
** Look for cysts after iodine staining
+
**Look for cysts after iodine staining
** Sensitivity 60-80% with one stool sample, up to 90% with three
+
**Sensitivity 60-80% with one stool sample, up to 90% with three
* Antigen assays are sometimes used during outbreaks or for screening
+
*Antigen assays are sometimes used during outbreaks or for screening
** Sensitivity 85-98% and specificity 90-100%
+
**Sensitivity 85-98% and specificity 90-100%
* PCR is becoming more common
+
*PCR is becoming more common
* String test
+
*String test
** Put a string down into small bowel and then pull it back; it should have bile
+
**Put a string down into small bowel and then pull it back; it should have bile
** Look with a microscope
+
**Look with a microscope
** Done when there is high suspicion but O&P negative
+
**Done when there is high suspicion but O&P negative
   
== Management ==
+
==Management==
   
* [[Is treated by::tinidazole]] 2 g po once
+
*[[Is treated by::Tinidazole]] 2 g po once, which is the gold standard
* [[Is treated by::metronidazole]] 250 mg po tid for 5 to 7 days
+
*[[Is treated by::Metronidazole]] 250 mg po tid for 5 to 7 days, but has a higher failure rate
* Alternatives: [[Is treated by::nitazoxanide]], [[Is treated by::albendazole]], [[Is treated by::paromomycin]], [[Is treated by::quinacrine]], and [[Is treated by::furazolidone]]
+
*Alternatives: [[Is treated by::nitazoxanide]], [[Is treated by::albendazole]], [[Is treated by::paromomycin]], [[Is treated by::quinacrine]], and [[Is treated by::furazolidone]]
  +
*Avoid caffeine, lactose, and smoking
  +
*Can consider [[Saccharomyces boulardii]] probiotics (Florastor)
   
 
{{DISPLAYTITLE:''Giardia lamblia''}}
 
{{DISPLAYTITLE:''Giardia lamblia''}}
[[Category:Protozoa]]
 
 
[[Category:Gastrointestinal infections]]
 
[[Category:Gastrointestinal infections]]
 
[[Category:Flagellates]]
  +
[[Category:Infectious diseases]]

Latest revision as of 13:07, 1 February 2022

  • A member of the Giardia that causes intestinal disease (giardiasis) in humans and animals
  • Also known as beaver fever

Background

Microbiology

  • Flagellated protozoan that infects the small bowel
  • Host specificity related to genotype ("assemblage")
    • Assemblages A & B infect humans, but also numerous non-human hosts including primates, dogs, cats, cattle, sheep, deer, rodents, horses, and beavers
    • Assemblages C & D affect dogs; E affects cattle, goats, sheep, and pigs; F affects cats; G affects rodents; and H affects marine vertebrates
  • Antigenic variation is determined by the variant-specific surface protein (VSP)
    • Replaced every few generations

Life Cycle

  • A cyst is ingested via fecal-oral contamination
  • In the small bowel, the cyst releases two trophozoites (free-living form) via excystation
  • Trophozoites multiply by binary fission
  • When they reach the large bowel, they encyst

Epidemiology

  • Worldwide distribution
  • Generally transmitted fecal-oral route (via environment), but person-to-person transmission is possible in daycares
  • Numerous animal reservoirs, not fully understood how important they are
  • Cysts can survive several months in cold water
  • Peak prevalence occurs in children of up to 15 to 30% in poor countries
  • Reinfection is common

Pathophysiology

  • Infected with as few as 10 to 25 cysts
  • Trophozoites colonize the upper small bowel, adhering to the mucosal enterocytes
  • Host response involves B- and T-cells, including production of IgM and IgG antibodies, possibly IgA antibodies as well
  • Causes villous atrophy, which can contribute to malabsorption
  • Inhibits disaccharidases, which contributes to lactose intolerance

Clinical Manifestations

  • Can have asymptomatic cyst passage (5 to 15%)
    • Can last up to 6 months in children
  • Most common syndrome is acute diarrhea (25 to 50%)
    • Incubation period 1 to 2 weeks
    • Usually presents after 7 to 10 days
    • Malaise, flatulence, cramps, bloating, nausea, anorexia, vomiting, and malabsorption
    • Sulfuric belching is classic
    • Fevers are uncommon but possible
  • Can also cause chronic diarrhea
    • More common in CVID, X-linked agammaglobulinemia, and AIDS
    • Malaise, occasional headache, diffuse abdominal and epigastric pain worse with food
    • May have malabsorption, often has weight loss
    • Symptoms can wax and wane, with periods of remission or constipation
  • Post-Giardia syndrome with irritable bowel syndrome and chronic fatigue may last for years
    • Can have significant malabsorption
  • Also, can have post-Giardia lactose intolerance lasting several weeks

Diagnosis

  • Stool microscopy
    • May see active trophozoites in saline wet prep
    • Look for cysts after iodine staining
    • Sensitivity 60-80% with one stool sample, up to 90% with three
  • Antigen assays are sometimes used during outbreaks or for screening
    • Sensitivity 85-98% and specificity 90-100%
  • PCR is becoming more common
  • String test
    • Put a string down into small bowel and then pull it back; it should have bile
    • Look with a microscope
    • Done when there is high suspicion but O&P negative

Management