Giardia Lamblia

Question 1

Other names

Answer 1

Giardia lamblia, Giardia duodenalis, Giardia intestinalis

Question 2

Habitat

Answer 2

Duodenum + upper jejunum

Question 3

Morphology

Answer 3

Trophozoite (feeding stage -> colonization)

• Median Pear shaped, 9-21 µm length and 5-5µm wide, dorsal convex, ventral concave & has sucking disc
• Behind sucking disc = pair of large curved and transverse median bodies
• Bilaterally symmetrical (all organs paired) – 2 parabasal bodies, blepharoplasts, axoneme, nuclei & 4 flagella pairs
• rapid movements w/ flasgella + by applying sucking disc onto epithelial surface)
• Large central karyosome (face like appearance)
• Cytoplasm =uniform and finely granulated.

Cyst

• 9-12 μm, smooth,ellipsoid shape
• 2-4 nuclei
• resistant to chlorine
• well defined wall - composed of polymers of galactosamine + proteins

Question 4

Hosts

Answer 4

humans, mamals, no intermediate host as has direct life cycle

Question 5

Life cycle

Answer 5

1. Ingest dormant cycts
2. Excysation - 1 cyst -> 2 trophozoite, emerge to active state in stomach & duodenum in the presence of gastric acid, pancreatic enzymes (chymotrypsin and trypsin) [acidic environment]
3. Asexual binary fission of trophozoite in lumen of prox bowel
4. Adhere to enterocytes via sucker [possibly via surface mannose-binding lectin]/float free
5. Encyst in the presence of more alk pH and bile salts whilst moving towards colon. [Begins with the appearance of encystation specific secretory vesicles (ESVs) in the cytoplasm of trophozoites, followed by production of cyst wall within 15 hours, w/i 24 hours after trophozoite is covered with these cyst wall proteins, flagella shorten, cytoplam condense, secrete thick hyaline wall]
6. Nucleur division of encysted trophozoites - > quadrinucleated mature cyst
7. Excysts and trophozoites(rare) out in feces [only cysts survive]

Question 6

Giardiasis Symptoms and Transmission

Answer 6

Non-ivasive

Transmision - feaco-oral/ingest contam water

Acute giardiasis (last 5-7D):

• acute watery diarrhea, abdominal cramp, bloating and flatulence. Occasionally nausea, vomiting, fever, rashes or constipation in some.
• Pus, blood and mucus are not seen in stool.

Chronic giardiasis (several weeks):

• Chronic diarrhea with steatorrhoea, malabsorption of vitamin A, protein and D-xylose, weight loss, malaise, nausea, anorexi
• Protuberance of abdomen, spindly extremities and stunted growth are most common sign in children.

Extra-intestinal- rare and sometimes urticarial and reactive arthritis

Complication:

• In adults, malabsorption syndrome and weight loss
• In children, growth retardation, delayed milestones achievements
• Giardiasis is self-limited disease and progression to chronic state is only 5% of infected people and death is rare.

Question 7

Pathogenesis & Diagnosis

Answer 7

• Adhesion to enterocytes, nutrient absorption interference
• enterocytes damage, villi atropy, crypt hyperplasia, intestinal hyperpermeability and brush boarder damage that causes a reduction in disaccharide enzyme secretion
• Trophozoites do not invade or penetrate surrounding tissue or enter blood stream.
• Giardiasis = osmotic diarrhea from malabsorption of electrolyte and fluid

Diagnosis

• Finding cysts in formed stools (trichrome or iron hematoxylin staining) >1 sample is recommended cysts in the stool can be highly irregular) and cysts may not be present until a week after symptoms appear [Trophozoites break up rapidly in the stool, and should not be relied upon]
• An Enzyme-Linked Immunosorbent Assay (ELISA) may be used to detect Giardia antigens in the stool, and is commercially available (highly sensitive).

Question 8

Giardiasis Treatment and Prevention

Answer 8

• Treatement - Metronidazole & Tinidazole (Tindamax) is also a first-line treatment. Nitazoxanide (inhibits trophozoite growth by disrupting their energy metabolism)
• Prevention - good hygeine practices, don’t drink/brush from untreated sources,