Giardia & Giardiasis

Question 1

Giardiasis

Answer 1

• major diarrheal disease worldwide
• more common in children than adults
• usually zoonosis

Question 2

Giardia organism

Answer 2

• flagellate protozoan (G. intestinalis)
• most commonly identified intestinal parasite in NA and world
• known to infect duodenum and small intestine of humans

Question 3

morphology of Giargia

Answer 3

• troph = existing and replicating in human intestine; invasive form!
• cyst = passed into environment; hardy and innate; infective form!

no intermediate host required

Question 4

body of Giardia supported by

Answer 4

cytoskeleton = microtubules and microribbons as well as …

axostyle = sheet of microtubules aising from bases of flagella (4 pairs) projecting beyond the end of cell, flexible, and also involved in movement

Question 5

thick cyst wall of Giardia

Answer 5

allows it to survive in environment

Question 6

important anatomic components of Giardia trophs

Answer 6

ventral or sucking disk used to attach to duodenum/jejunum
-increases neg pressure, holding Giargia in place, and can release Giardia to allow it to move along intestinal epithelium

Question 7

the parabasal/medial body of Giardia

Answer 7

enigmatic microtubule structure of unknown function; forms a “crooked smile”

• cytoskeleton midline
• unique to Giardia and helps define it morphologically
• proposed as the assembly site for microtubule proteins to be incorporated into the ventral disk

Question 8

Giardia cysts

Answer 8

contain organisms that have undergone nuclear rep but before CYTOKINESIS = 4 nuclei (mature cysts)

environmentally hardy and double layered (outer filamentous layer + inner membraneous layers)

resting phase so have only 10-20% of metabolic activity of trophs

Question 9

pathogenesis of Giardia

Answer 9

damage to brush border of epithelium
- adhesion of trophs; cause increased epithelial permeability
- mediated by surface mannose-binding lectins
- loss/damage of intestinal epithelial surface with villus flattening and atrophy (could track “footsteps”)

altered enzyme activities
- inhibition of disaccharidase (no absorption of sugar)
- increased adenylate cyclase = altered gut motility and fluid hypersecretion
- proteinases, cysteine proteases

enterotoxins = postulated 58kDa inducing inducing chloride secretion

immunologic rxns = activated host T lymphocytes mediated enterocytic injury

overgrowth of enteric bacterial flora

Question 10

excystation of Giardia

Answer 10

pH 1.3 to 2.7; within 5 minutes
produces trophs and attaches to epis

Question 11

what is the result of the pathogenesis of Giardia?

Answer 11

apoptosis of intestinal epithelium

malabsorption of sugars, fas, and fat-sol vitamins (A & E), weight loss, and diarrhea

Question 12

T or F. G. intestinalis is genetically heterogenous

Answer 12

T! with 8 genetically distinct genotypes or assemblages, designated A-H

Question 13

This species of Giardia affect humans

Answer 13

G. intestinalis

Question 14

Genotypically diverse isolates of Giardia species may vary in their ability to produce _________ changes in the small intestine epithelium and to impair ___, ____, and solute transport

Answer 14

morphologic; fluid; electrolyte

Question 15

T or F. Giadia trophs are passed in stool and survive in the environment

Answer 15

F! they are passed but they do not survive in the environment

Question 16

where do Giardia trophs localize in the human GI tract?

Answer 16

small intestine (proximal small bowel)
- attach to duodenum and jejunum via adhesive disk on ventral surface of the organism

Question 17

what happens to the Giardia trophs that do not adhere to small bowel mucosa?

Answer 17

they move into large bowel
- evert to cyst form = infectious; passed out in the stool
some trophs also in stool but not infectious

Question 18

what factors promote Giardia encystation?

Answer 18

bile sales in large intestine and bacterial flora

Question 19

transmission of Giardia

Answer 19

• fecal-oral
• infective dos = low in humans; 10-25 cysts can cause clinical disease and ingestion of more than 25 = 100% infection rate
• person to person transmission is associated with poor hygiene and sanitation
• water-borne transmission epidemics
• food-borne epidemics
• venereal transmission (fecal-oral)

Question 20

asymptomatic carriage of Giardia

Answer 20

carrier rates = 30-60% found in children in daycare centers or institutions

• high-risk patient groups = children, travellers, immunocompromised, men who have sex with men

Question 21

symptoms of acute giardiasis

Answer 21

• diarrhea
• malaise
• foul-smelling fatty stools
• cramps and bloating
• nausea
• weight loss
• vomiting
• fever
• constipation

can last from wks to months

Question 22

symptoms of chronic giardiasis

Answer 22

loos stools (NOT diarrhea)
foul-smelling fatty stools (malabsorption)
profound weight loss
malabsorption of nutrients
fatigue
depression
cramping and bloating
burping and flatulence

Question 23

diagnosis of Giardiasis

Answer 23

• direct visualization of trophs and cysts
  > fecal specimens (O&P exam); trophs and cysts
  > tissue biopsy (trophs at top; not invading)

> cysts = most commonly seen in wet mount
trophs = permanent mounts (trichrome or iron-hematoxylin stains

repeated sampling may be necessary to make a diagnosis bc shed irregularly; sampling must be spaced out; at least one day in between stool tests

• direct fluorescent antibody
• enzyme immunoassay

Question 24

string test procedure for Giardia

Answer 24

• last resort if other methods do not work
• pt swallows capsule with gelatin and tightly wound string; other end of string taped to cheek
• after 5h = string removed from pt and wet mount of the adherent material is carried out
• can also make a permanent smear