Giardia
• Flagellated protozoan parasite found in the GIT of animals including man.
• Prevalence: General population cats; <1% to 13.6% (most reports - 10%). Shelter cats: Can be as high as 80% in cats
housed in high density rooms. [Worth noting that prevalence data may depend on the sensitivity of the test used: IFA – 14%,
IDEXX SNAP Giardia test – 11%]
• Although prevalence can be high, clinical disease is rare, and often not dependent on prevalence – more often dependent
on age (young cats, higher incidence of signs).
Life cycle
• Direct with infection via oral route. Entire development occurs in the GIT. Cysts in feces.
• 2 forms: 1) teardrop-shaped trophozoite (active motile form found in GIT), 2) cyst or dormant resistant stage responsible
for transmission.
• Cyst capable of surviving for several months outside host in wet cold condition. Can also survive chlorinated water.
Very susceptible to desiccation under dry hot conditions.
Clinical findings.
• Most infections are asymptomatic.
• Diarrhea is main sign. May be acute, short-lived, intermittent, or chronic. Feces pale, malodorous, and steatorrheic.
May see weight loss (diarrhea) but rarely inappetence.
Diagnosis.
• Clinical signs and tests (CBC, serum chemistry, radiology etc) are non-specific.
• Unequivocal diagnosis relies on finding cysts or trophozoites (or products of these) feces or samples taken from the
GIT.
Fecal smear.
• Easy, non-invasive, and very specific but low sensitivity. Trophozoites more likely passed in loose feces, especially
in cats.
• Drop of fecal material mixed with a drop of normal saline, cover slipped, examine at 40X. Trophozoites easily identified
by rapid forward motion, and concave ventral disc. Trichomonads (the only other organism that looks like Giardia has a rolling motion, no concave disc, single nucleus, and an undulating membrane. Stain organisms with Lugols iodine to
confirm.
Zinc sulfate concentration technique (ZSCT).
• Use a 1.18 SG ZnSO4 solution with centrifugation. Needs trained personal to conduct test as cyst shedding (particularly in dogs) is variable (from
a few to 50,000/gm of feces in 3 days)
• 1.18 SG ZnSO4 solution may not float heavier eggs (e.g. Taenia spp.) so can use a modified 1.27 SG Sheather sugar solution which will also
get Giardia. [Dryden's Modified Sheather's Solution (SG 1.27): 454 gm granulated sugar, 355 ml tap water, 6 ml formaldehyde.
Dissolve sugar (gentle heat), check SG (hydrometer), filter (course filter paper) if not clear.]
• Performing 3 tests on fresh fecal samples collected over a 3 to 5 day period (because cysts are shed intermittently)
is considered the gold standard. One test is about 70% efficacious, 2 tests are about 93% efficacious, and 3 tests are about
between 95 and 100% efficacious.
• Problem:- not very practical in a private practice situation. Cysts may be confused with yeast
• May ship samples refrigerated (cysts live for 2 days at 4C, but will not survive formalin). ZSCT also excellent for
nematode eggs.
