Comparison of Giardia duodenalis point-of-care antigen faecal tests to reference laboratory assays in non-symptomatic dogs

Abstract

Giardia duodenalis is one of the most prevalent enteric parasites of dogs. Point-of-care antigen tests (POC) are rapid and do not require additional equipment, or a specialised diagnostic laboratory. The aim of this study was to compare diagnostic tests available in veterinary practices and in a diagnostic laboratory for the detection of G. duodenalis on a cohort of group-housed dogs from New South Wales, Australia. Two different POC tests were used for the detection of G. duodenalis. Laboratory tests used were the multiplexed-tandem PCR panel (MT-PCR) that includes detection of G. duodenalis DNA, and two reference tests (an in-house TaqMan real-time PCR and a direct immunofluorescence assay, DFA). Canine faecal samples (n = 40) were tested simultaneously for the detection of G. duodenalis. Using either DFA or TaqMan real-time PCR as reference tests, 77.5% (31/40) and 82.5% (33/40) of dogs tested positive, respectively. Agreement (Kappa) between the DFA and TaqMan real-time PCR was 0.84 (95% CI 0.64 to 1.00). There was substantial G. duodenalis test outcome agreement between the two POC tests, Kappa = 0.75. Combining the two POC tests yielded 77% sensitivity and 100% specificity with DFA as reference, and for TaqMan real-time PCR it was 73% sensitivity and 100% specificity. The MT-PCR was in excellent agreement with each reference test, DFA or TaqMan real-time PCR. Due to the high specificity of both POC tests, they can be confidently used as rule-in diagnostics. Confirmatory testing that detects different biological parameters such as DNA, e.g. PCR (inc. MT-PCR), should be implemented before concluding that a dog is negative for the presence of G. duodenalis.

Keywords: Canine; DFA; Diagnosis; Diagnostics; Giardia; Giardia intestinalis; Multiplex-tandem PCR; POC diagnostics; Parasitism; RAT; Real-time PCR.