- 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
