Giardia spp. infection is difficult to diagnose and so fecal flotation is sometimes combined with fecal antigen testing. Dogs are most frequently infected with genetic assemblages that are distinct from those that most commonly infect humans. The objectives of this study were to determine the most common Giardia spp. assemblages that infect dogs and to determine whether a Giardia antigen assay (SNAP® Giardia, IDEXX Laboratories, Portland, Maine) that is labeled for use with canine feces detects the assemblages commonly isolated from dogs.
Fecal samples were collected from dogs evaluated in small animal clinics in north central Colorado. An aliquot of feces was assayed immediately using the SNAP® Giardia assay and an aliquot was stored at 4°C until transported to Colorado State University for performance of fecal flotation by zinc sulfate centrifugation. All samples positive for Giardia cysts or Giardia antigen were assessed in a PCR assay and genotyped using previously validated techniques.
Of the 220 samples, 25 (11.4%) were positive for Giardia spp. antigen or cysts. Of the 17 samples giving a positive PCR reaction, 4 were assemblage C and 13 were assemblage D. All of these samples were positive in the SNAP® Giardia assay.
All of the dogs in this study were infected with Giardia assemblages most commonly isolated from dogs; assemblages usually found in people were not detected. The SNAP® Giardia assay detected all of the assemblages C and D isolates and so is an accurate test for the detection of Giardia antigen in feces of dogs.