Molecular typing of Giardia duodenalis isolates from German travellers

Giardia duodenalis isolates from German travellers returning from tropical areas were characterised by PCR amplification and sequencing of fragments of the beta-giardin (bg), glutamate dehydrogenase (gdh) and triose phosphate isomerase (tpi) genes. Assignment of isolates to specific G. duodenalis assemblages was found to differ according to the marker used. Indeed, at the bg locus, assemblages A and B were identified, with a higher prevalence of the former over the latter, whereas at the tpi and gdh loci, most samples were classified as assemblage B. In agreement with previous studies, sequence analysis showed that assemblage B isolates have a higher genetic polymorphism than assemblage A isolates, and novel variants were described. The degree of polymorphism was shown in a graphical representation of the polymorphic sites generating a novel sequence, the heterogeneous positions common to assemblages A and B (double peaks), that may represent mixed assemblage infection and the heterogeneous positions detected at random sites. Notably, assemblage D, which is considered to be adapted to dogs, was found at the gdh locus in two samples originating from southern Asia, as novel genotypes. By comparing the geographical origin of the infected cases and the number of German travellers visiting the areas considered, India and west Africa appeared to be the areas associated to the highest risk of acquiring Giardia infection. The analysis of the geographical distribution of the genotypes did not suggest any particular geographical clustering pattern, but it may be useful to evaluate these results with a higher number of isolates. Most of the samples typed at the three markers could not be assigned unequivocally to either assemblage A or B, and this was confirmed also by a real-time PCR assay, using a set of assemblage-specific primers. The results of this study reinforce the notion that genetic exchanges and allelic sequence heterogeneity represent major obstacles towards understanding the epidemiology of giardiasis and that exposure to Giardia parasites in endemic areas often results in mixed infections in returning travellers.