Analysis of nucleotide variation within the triose-phosphate isomerase gene of Giardia duodenalis from sheep and its zoonotic implications.

This study explored the genetic composition of Giardia in fecal samples from 284 individual lambs on pasture-based sheep farms in three regions of Victoria, Australia. An approach, combining targeted sequencing, phylogenetic analysis and PCR-coupled restriction endonuclease fingerprinting, was used to identify and genetically categorize Giardia present in 43 (15.1%) of the 284 samples and to infer their zoonotic potential. The specific identity and genetic classification were based on the phylogenetic analysis of sequence data for a portion of the triose-phosphate isomerase gene. Fourteen different sequence variants (including seven sequences that contained between one and five polymorphic sites) representing two distinct assemblages of Giardia (recognized in the current literature) were defined, of which 13 were new records. One dominant sequence type (with accession no. GQ444447, representing a genotype within assemblage A) has been detected previously in humans and is thus considered to be of zoonotic potential. (Nucleotide sequences reported in this article are available in the GenBank database under accession nos. GQ444447-GQ444451 and GQ444454-GQ444462).