Giardia lamblia

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

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, cars, 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