Giardia, cryptosporidia, tritrichomonas (Proceedings)


Giardia, cryptosporidia, tritrichomonas (Proceedings)

Nov 01, 2010


     • 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.


     • 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.