Giardia lamblia: Difference between revisions
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Giardia lamblia
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+ | *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 [[Usual 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== |
| − | * |
+ | *[[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, 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]] |
| − | * |
+ | *Avoid caffeine, lactose, and smoking |
| − | * |
+ | *Can consider [[Saccharomyces boulardii]] probiotics (Florastor) |
{{DISPLAYTITLE:''Giardia lamblia''}} |
{{DISPLAYTITLE:''Giardia lamblia''}} |
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[[Category:Gastrointestinal infections]] |
[[Category:Gastrointestinal infections]] |
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| + | [[Category:Infectious diseases]] |
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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
- Tinidazole 2 g po once, which is the gold standard
- Metronidazole 250 mg po tid for 5 to 7 days, but has a higher failure rate
- Alternatives: nitazoxanide, albendazole, paromomycin, quinacrine, and furazolidone
- Avoid caffeine, lactose, and smoking
- Can consider Saccharomyces boulardii probiotics (Florastor)
