Giardia lamblia

From IDWiki
Giardia lamblia / (Redirected from Giardiasis)
  • 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