Giardia lamblia

• 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

• 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