Comparison of multilocus genotyping and a commercial beta-giardin qPCR assay for detection of Giardia duodenalis zoonotic assemblages in cat and dog samples

Abstract

Background: Giardia duodenalis is a protozoan of dogs and cats that comprises several genotypes (assemblages A–G). The common assemblages affecting small animals (C, D, F, G) are not associated with disease in humans. However, assemblages A and B can be zoonotic. Several assays can be used for detection of G. duodenalis, but there is a need for an accurate and faster detection method for G. duodenalis zoonotic assemblages. The aim of this study was to compare a beta-giardin quantitative polymerase chain reaction (PCR) (bg-qPCR) to a standard multilocus genotyping technique for detection of G. duodenalis zoonotic assemblages in dog and cat feces. Methods: Canine and feline fecal samples submitted to a commercial laboratory (Antech Diagnostics) that tested positive for Giardia by centrifugal flotation, Giardia enzyme-linked immunosorbent assay (ELISA), and quantitative small subunit ribosomal ribonucleic acid PCR or those positive for Giardia spp. by a commercial direct fluorescent assay were included in this study (140 cases with zoonotic and non-zoonotic assemblages). The bg-qPCR assay was optimized and then all samples were assessed by both methods. Agreement among the two methods was assessed by Cohen’s kappa agreement. Results: A total of 140 samples that were previously positive for Giardia were analyzed by both bg-qPCR and multilocus genotyping. Both bg-qPCR and multilocus genotyping identified 70 of 76 (92.10%) of assemblage A and B samples. A total of 64 (n = 40 for assemblage A and n = 24 for assemblage B) of 76 samples yielded concordant results, with both diagnostic techniques giving a Cohen’s kappa agreement value of 0.828. Non-zoonotic assemblages were amplified only by multilocus genotyping in 55 samples, and 9 samples were negative for both methods. Multilocus genotyping reported mixed infections in 23 cases and included A/D (1 dog), B/C (1 dog), B/F (1 dog; 2 cats), and C/D (18 dogs). Conclusions: For the zoonotic assemblages, the results between multilocus genotyping and the bg-qPCR agreed for most cases. These data support the bg-qPCR as a less expensive and laborious option to determine zoonotic Giardia A/B assemblages in feces of dogs and cats.