Epidemiological and molecular evidence supports the zoonotic transmission of <e1>Giardia</e1> among humans and dogs living in the same community

<e1>Giardia duodenalis</e1> isolates recovered from humans and dogs living in the same locality in a remote tea-growing community of northeast India were characterized at 3 different loci; the SSU-rDNA, elongation factor 1-alpha (ef1-α) and triose phosphate isomerase (tpi) gene. Phylogenetic analysis of the SSU-rDNA and ef1-α genes provided poor genetic resolution of the isolates within various assemblages, stressing the importance of using multiple loci when inferring genotypes to <e1>Giardia</e1>. Analysis of the tpi gene provided better genetic resolution and placed canine <e1>Giardia</e1> isolates within the genetic groupings of human isolates (Assemblages A and B). Further evidence for zoonotic transmission was supported by epidemiological data showing a highly significant association between the prevalence of <e1>Giardia</e1> in humans and presence of a <e1>Giardia</e1>-positive dog in the same household (odds ratio 3·01, 95% CI, 1·11, 8·39, <e1>P</e1>=0·0000).