Lecture 15: Giardiasis Flashcards
What is the most common intestinal commensal or parasite in vertebrates
Giardia
Where in the intestines does giardia infect
Upper intestinal tracts
What Giardia infects rodents
G. Muris
What Giardia infects muskrats and voles
G. Microti
what Giardia infects amphibians
G. Agillis
What Giardia infects birds
G. Psittaci and G. Ardeae
What Giardia infects reptiles
G. Varani
Describe the key characteristics of Giardia Trophozoite
- Pyriform (tear drop) shape
- Two nuclei
- Two median bodies
- Five pairs of flagella
What are the key characteristics of Giardia cysts
- Thick walled
- Contain 4 nuclei
How many trophozoites are released from a cyst
2
What triggers excystation
Gastric acid, pancreatic enzymes and bile salts
What species does genetic assemblage do A and B infect
Wide range of domestic and wild animals including humans
What does subassemblage AI infect
Domestic livestocks and pets
What does subassemblage AUII primary infect
Humans
What species does the C and D genetic assemblage infect
Dogs and wild canids
What species does E of the genetic assemblage infect
Hoofed stock- cattle, sheep, goats, pigs, horses
What species does F of the genetic assemblage infect
Cats
What species does G of the genetic assemblage usually infect
Rodents
What species does H of the genetic assemblage usually infect
Seals
How is Giardia transmitted
- Direct ingestion of cysts
- Indirect ingestion of contaminated water, food, transport hosts, infected prey, or fomites
- Re-infected from animal fur when they groom
What is the prepatent period in cats
5-16 days (mean 10)
What is the prepatent period in dogs
4-12 days (mean 8)
How does Giardia use attachment as a virulence factor
Ventral adhesive disc and surface lectins enable attachment to and colonization of the intestinal endothelium
How does Giardia use circumvention of the natural factors of the intestinal lumen as a virulence factor
Flagellar motility enables re-localization to new endothelial cells during colonization, and VSPs potentially help protect against luminal proteases, oxygen and free radicals
how does Giardia alter the host innate defense to use as a virulence factor
Released arginine deiminase and down regulate the epithelial production of nitric oxide
How does Giardia use antigenic variation as a virulence factor
VSP on the Trophozoite surface switches to avoid Ig-A directed clearance
How does Giardia use anti-inflammatory modifications as virulence factor
Unknown Trophozoite products have anti-inflammatory roles
How does Giardia survive in the stomach (virulence factor)
Differentiation into cyst
What is a variant specific surface protein (VSP)
Cysteine rich, surface proteins that covers entire Giardia cell
Main function is immune evasion
How does the VSP evade the immune system
On-off switching of the expression of genes encoding VSP
What is the pathogenesis of giardia
- Ingested cysts release 2 trophozoites in duodenum
- Trophozoites mature and attack to the brush border of the villus epithelium via ventral adhesive disks and surface molecules
Where are trophozoites commonly found in dog intestines
Duodenum to ileum
Where are trophozoites commonly found in cat intestines
Jejunum to ileum
What are some proposed mechanisms of giardiasis
- Apoptosis of enterocytes
- Loss of epithelial barrier function
- Hypersecretion of Cl-
- Diffuse microvillus shortening
- Immune reaction
- Inhibition of brush border enzymes and trypsin
- Interference with bile salt metabolism
What are some clinical manifestations of Giardia in cats and dogs
Acute, chronic or intermittent diarrhea or soft tools. Typically light colored, mucoid, malodorous
May contains fat
Dog may lose weight and vomit
What are some clinical manifestations of Giardia in domestic hoofed stock
Diarrhea pasty to fluid, mucoid, decreased appetite, loss or failure to gain weight
T or F: Giardia is uncommon in horses
True
What are some clinical manifestations of Giardia in non-human primates
Diarrhea, lethargy, weight loss, vomiting
What are the two species of Giardia from birds
- Giardia psittaci
- Giardia ardae
What birds have. G. Psittaci
Parrots
What birds have G. Ardeae
Herons, egrets, storks
What are some clinical manifestations of Giardia in avian species
- Diarrhea- mucoid, malodorous, anorexia and depression
- Feather plucking
- Poor growth and high mortality in cockatiels, budgergiars
What is the most implicated species in zoonotic transmission of Giardia
Beavers
How do you diagnose Giardia
- Clinical suspicion- history and diarrhea (unresponsive to Antiboitoics)
- Microscopic examination of fresh species
- Fecal immunoassays
- PCR
What are some fecal tests that you can run for Giardia
- Direct saline smear
- Fecal float
What fecal test/microscopic examination do you want to use for motile trophozoites of Giardia
Direct saline smear
What fecal test/microscopic examination do you want to use for detection of cysts
Fecal float with zinc sulfate flotation
What is A, B and C
A. Giardia cyst
B. Giardia Trophozoite
C. Detached trophozoites in intestinal lumen
A fecal flotation was performed on a cat with suspected Giardia. What solution was used in the fecal float on the left vs the right
Left: sheathes sugar solution the eggs will not float with a specific gravity of 1.25
Right: zinc sulfate solution which has a lower specific gravity ~1.18 allowing the cysts to float
How do you prevent giardiasis
- Bathe affected dogs and cats to remove cysts from hair
- Feces removed daily
- Surfaces sanitized
