Giardia & Giardiasis Flashcards
Giardiasis
- major diarrheal disease worldwide
- more common in children than adults
- usually zoonosis
Giardia organism
- flagellate protozoan (G. intestinalis)
- most commonly identified intestinal parasite in NA and world
- known to infect duodenum and small intestine of humans
morphology of Giargia
- troph = existing and replicating in human intestine; invasive form!
- cyst = passed into environment; hardy and innate; infective form!
no intermediate host required
body of Giardia supported by
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
thick cyst wall of Giardia
allows it to survive in environment
important anatomic components of Giardia trophs
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
the parabasal/medial body of Giardia
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
Giardia cysts
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
pathogenesis of Giardia
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
excystation of Giardia
pH 1.3 to 2.7; within 5 minutes
produces trophs and attaches to epis
what is the result of the pathogenesis of Giardia?
apoptosis of intestinal epithelium
malabsorption of sugars, fas, and fat-sol vitamins (A & E), weight loss, and diarrhea
T or F. G. intestinalis is genetically heterogenous
T! with 8 genetically distinct genotypes or assemblages, designated A-H
This species of Giardia affect humans
G. intestinalis
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
morphologic; fluid; electrolyte
T or F. Giadia trophs are passed in stool and survive in the environment
F! they are passed but they do not survive in the environment
where do Giardia trophs localize in the human GI tract?
small intestine (proximal small bowel)
- attach to duodenum and jejunum via adhesive disk on ventral surface of the organism
what happens to the Giardia trophs that do not adhere to small bowel mucosa?
they move into large bowel
- evert to cyst form = infectious; passed out in the stool
some trophs also in stool but not infectious
what factors promote Giardia encystation?
bile sales in large intestine and bacterial flora
transmission of Giardia
- 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)
asymptomatic carriage of Giardia
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
symptoms of acute giardiasis
- diarrhea
- malaise
- foul-smelling fatty stools
- cramps and bloating
- nausea
- weight loss
- vomiting
- fever
- constipation
can last from wks to months
symptoms of chronic giardiasis
loos stools (NOT diarrhea)
foul-smelling fatty stools (malabsorption)
profound weight loss
malabsorption of nutrients
fatigue
depression
cramping and bloating
burping and flatulence
diagnosis of Giardiasis
- 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
string test procedure for Giardia
- 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
