The molecular characterisation of Giardia from dogs in southern Germany.

Faecal samples were obtained randomly from asymptomatic dogs visiting veterinary clinics (kept individually) and sanctuaries (kept in groups) in southern Germany. Of 60 Giardia positive samples, 55 samples successfully amplified at the 18S rDNA locus. In both dogs kept individually and dogs kept in groups, assemblage A was most prevalent (overall, n=33, 60%), followed by mixed infections with assemblages A&C (overall, n=15, 27.3%), while assemblages C&D alone were less often detected (overall, n=5, 9.1% and n=2, 3.6%). The occurrence of zoonotic genotypes was more prevalent in individual than in group dogs. Genotyping at the gdh locus confirmed the 18S results and clustered the assemblage A isolates into A-I. This is the first large-scale urban survey in Central Europe, which has not only confirmed the high prevalence of Giardia in asymptomatic domestic dogs, but has also shown that the zoonotic assemblage A occurs commonly in domestic dogs living in urban environments, and more frequently than the dog-specific assemblage. Although it was not possible to obtain samples from pet owners in this study, the results demonstrate that a significant proportion of dogs in urban areas of southern Germany harbour zoonotic Giardia, and should thus be considered a potential reservoir for infection in humans.

Comparative evaluation of Giardia duodenalis sequence data.

A review of the Giardia duodenalis sequences currently available on the GenBank database was completed to compare the different genotyping loci (small subunit ribosomal DNA, glutamate dehydrogenase, triose-phosphate isomerase and beta giardin) for their ability to discern assemblage and subassemblage groups and infer phylogenetic relationships. In total, 405 Giardia duodenalis sequences were sorted and aligned to examine the substitutions within and between the assemblages - A and B (zoonotic), C and D (dogs), E (livestock), F (cats) and G (rodents). It was found that all of the genes could reproducibly group isolates into their assemblages and that the AI/AII subassemblage groups were robust and identifiable at all loci. However, the assemblage B subgroups were not reproducible at half of the loci (small subunit ribosomal DNA and beta giardin), not due to their conserved nature, but because there was insufficient sequence data of reference isolates available for comparison. It is anticipated that further investigation of these loci may reveal the core subgroups of this medically important and zoonotic assemblage and also those of others. The closer, more recent, phylogenetic relationships amongst the assemblages appear to be resolved; however, more sequence data from the current loci, and possibly new loci, will be required to establish the remaining relationships.