Molecular typing ofGiardia duodenalisin humans in Queensland – first report of Assemblage E

Abstract

SUMMARYLittle is known about the genetic diversity of the protozoan parasite,Giardia duodenalis,infecting humans in Queensland, Australia. The present study typed 88 microscopicallyGiardia-positive isolates using assemblage-specific primers at the triose phosphate isomerase (tpi) gene and sequenced a subset of isolates at the glutamate dehydrogenase (gdh) gene (n= 30) andtpilocus (n= 27). Using thetpi-assemblage specific primers,G. duodenalisassemblage A and assemblage B were detected in 50% (44/88) and 38·6% (34/88) of samples, respectively. Mixed infections with assemblages A and B were identified in 4·5% (4/88) and assemblage E was identified in 6·8% (6/88) of samples. Sequence analysis at thegdhandtpiloci also confirmed the presence of assemblage E in these isolates. Cyst numbers per gram of feces (g−1) were determined using quantitative polymerase chain reaction and of the isolates that were typed as assemblage E, cyst numbers ranged 13·8–68·3 × 106cysts g−1. This is the first report of assemblage E in humans in Australia, indicating that in certain settings, this assemblage may be zoonotic.