The SNAP Giardia Test provides sensitive andspecific detection of Giardia antigen in dogs
Study shows the VetScan, Witness, and Anigen Giardia tests
demonstrate poor sensitivity and specificity for Giardia antigen
Introduction
Giardia is a single-celled protozoan parasite that causes intestinal
infections in both dogs and cats. Dogs become infected when they
ingest Giardia cysts that may be present in water or other areas ofthe environment that have been contaminated with feces.1
Symptoms are more visible in puppies and younger dogs than inolder dogs and can be acute, transient, intermittent, or chronic innature. In some cases, dogs will exhibit diarrhea that is soft, frothy,greasy, and with a strong odor or excessive mucus.2
Rapid diagnosis of giardiasis in dogs with diarrhea is very
important and several in-clinic tests are available to detect Giardiaspecific antigens in the feces. However, a direct comparison of
the sensitivity and specificity for antigen detection between thesedifferent tests has not yet been performed.

The performance of all four in-clinic tests is shown in Table 1. The
SNAP Giardia Test had higher sensitivity and specificity than any of
the other three tests.
In addition, the VetScan Canine Giardia Rapid Test produced
invalid results on 6 samples for failing to develop positive control
line (representative images shown in Figure 1). One of them also
failed on the Witness Giardia Test. These 6 samples were excluded
from calculation of sensitivity and specificity, even though all hadvalid results by the SNAP Giardia Test and the Anigen test.

IDEXX Laboratories conducted a study to determine theperformance of four in-clinic diagnostic tests for detection ofGiardia antigen in canine feces: the SNAP® Giardia Test, theVetScan® Giardia Rapid Test (Abaxis), the Witness® Giardia Test(Zoetis), and the Anigen® Rapid CPV/CCV/Giardia Test (BioNote).

Figure 1. Four representative samples with valid SNAP Giardia Test results andinvalid VetScan Canine Giardia Rapid Test results.

Study design

Summary and conclusions

Study samples were sourced from fecal samples submitted toIDEXX Reference Laboratories for ova and parasites testing using
centrifugal flotation that included identification of Giardia cysts.
They were further tested for Giardia-specific antigen using theThermo Scientific™ ProSpecT™ Giardia Microplate Assay.
Because discordant results between testing for cysts and antigen
are possible, positive samples were defined as those testing positiveby both reference methods while negative samples were definedas those testing negative on both reference methods. A total of 95
positive samples and 81 negative samples were identified.
These samples were then tested using the four in-clinic tests
following manufacturers’ protocols. For calculation of sensitivity
and specificity, test results were compared to the results obtainedby the reference methods.

Results• The Witness test missed nearly 4 in 10 samples that werepositive for the presence of both Giardia cysts and Giardiaspecific antigens; the Vetscan test missed nearly 3 in 10; theAnigen test missed 2 in 10.
•	The Witness, Vetscan, and Anigen tests also incorrectly
identified 13–30% of Giardia cyst-free and Giardia antigen-freedogs as positive.
• The Abaxis VetScan Canine Giardia Rapid Test was found to beprone to having invalid test results.
• Poor-performing Giardia tests could lead to misdiagnosis anddelay the initiation of appropriate therapy in a dog with diarrhea
caused by giardiasis.
• IDEXX ELISA-based tests have proven accuracy in the field fornearly 20 years and continue to demonstrate superior accuracy
in the veterinary practice.

In-clinic test

Sensitivity

Specificity

References

SNAP Giardia Test

89.2%

100%

VetScan Canine Giardia Rapid Test

71.0%

83.1%

1. Payne PA, Artzer M. The biology and control of Giardia spp. andTritrichomonas foetus. Vet Clin North Am Small Anim Pract. 2009;39(6):993–1007.

Witness Giardia Test

63.7%

86.8%

Anigen Rapid CPV/CCV/Giardia Test

78.5%

70.1%

Table 1. Comparative performance of in-clinic Giardia antigen test kits

2. Ballweber LR, Xiao L, Bowman DD, Kahn G, Cama VA. Giardiasis in dogs
and cats: update on epidemiology and public health significance. Trends
Parasitol. 2010;26(4):180–189.

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