Giardia lamblia

Giardia lamblia


Giardia intestinalis/ Giardia lamblia

  • Man is the main reservoir
  • Inhabit duodenum, jejunum & upper ileum

Infection is common in: 

  • Selective IgA deficiency
  • G. intestinalis exists in 2 stages – trophozoite & cyst

Morphology of Giardia lamblia trophozoite

  • Pear shaped, rounded anterior end, posterior end pointed (looks like monkey face)
  • Size: 12 to 15 µm long x 5 to 9 µm wide
  • Dorsal surface convex, ventral surface concave
  • Ventral surface bears sucking disk to adhere to surface of intestinal cell

Bilaterally symmetrical: 

  • 2 nuclei, 2 axostyles, 4 pairs of flagella (2 anterior, 2 posterior, 2 ventral, and 2 caudal) •
  • Actively moving and feeding stage
  • Habitat: small intestine – May invade the common bile

Morphology of Giardia lamblia cysts

  • Ovoid in shape
  • 8-12 µm long x 7-10 µm wide
  • Thick cyst wall
  • 4 nuclei present, either clustered at on end or present in pairs at opposite ends
  • Axostyle runs diagonally through the cyst
  • Flagella shorten and are retracted within cyst – provide internal support
  • The cyst forms as trophozoites become dehydrated when they pass through the large intestine
  • Cyst may remain viable in the external environment usually water, for many months.

Infective form

Mature cyst passed in feces of man

Routes of transmission 

  • Feco-oral
  • Ingestion of contaminated water – most important
  • Ingestion of contaminated food
  • Person to person – day care, nursing homes, mental asylums (poor hygiene)
  • Sexual – sexually active homosexual males

Life Cycle

  • Acquire infection – ingestion of mature cysts
  • Excystation occurs in stomach & duodenum within 30 minutes
  • 2 trophozoites hatch from one cyst
  • Trophozoites multiply by binary fission & colonize in duodenum & upper jejunum
  • Trophozoites adhere to enterocytes by ventral suckers
  • Encystation occurs in transit down the colon
  • Axonemes retract, cytoplasm condense & thin tough hyaline wall is secreted
  • Encysted trophozoite undergo nuclear division – mature quadrinucleate cyst

Pathology

  • Do not invade tissues
  • Feed on mucous secretions
  • May localise in biliary tract to avoid the acidity of duodenum
  • Cause inflammation of duodenum & jejunum
  • Cause malabsorption as the parasite coats the mucosa & damage epithelial brush border
  • Stool contains large amounts of mucous & fat but no blood

Exam Important

Giardia intestinalis/ Giardia lamblia

  • Inhabit duodenum, jejunum & upper ileum

Infection is common in: 

  • Selective IgA deficiency
  • G. intestinalis exists in 2 stages – trophozoite & cyst

Morphology of Giardia lamblia trophozoite

  • Pear shaped, rounded anterior end, posterior end pointed (looks like monkey face)

Bilaterally symmetrical: 

  • 2 nuclei, 2 axostyles, 4 pairs of flagella (2 anterior, 2 posterior, 2 ventral, and 2 caudal) •

Morphology of Giardia lamblia cysts

  • 4 nuclei present, either clustered at on end or present in pairs at opposite ends

Infective form

  • Mature cyst passed in feces of man

Routes of transmission 

  • Feco-oral
  • Ingestion of contaminated water – most important
  • Ingestion of contaminated food
  • Person to person – day care, nursing homes, mental asylums (poor hygiene)
  • Sexual – sexually active homosexual males

Pathology

  • Do not invade tissues
  • Feed on mucous secretions
  • May localise in biliary tract to avoid the acidity of duodenum
  • Cause inflammation of duodenum & jejunum
  • Cause malabsorption as the parasite coats the mucosa & damage epithelial brush border
  • Stool contains large amounts of mucous & fat but no blood
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