Epidemiological distribution of genotypes of Giardia duodenalis in humans in Spain

Abstract

Background: Although the distribution of Giardia duodenalis genotypes in humans has been increasingly reported in recent years, data on possible differences in pathogen transmission between age groups and virulence between genotypes are scarce. The purpose of this study is to investigate the genetic diversity of G. duodenalis in humans in Spain and compare the distribution of G. duodenalis assemblages A and B between children and adults and clinical presentations between the two genotypes.

Methods: In the present study, 125 microscopy-positive fecal samples were collected from humans in Spain over a 7-year period. PCR and sequence analyses of the triosephosphate isomerase, β-giardin and glutamate dehydrogenase genes were used to identify the multilocus genotypes of G. duodenalis.

Results: Sequence analysis of three genetic loci identified both G. duodenalis assemblages A (29) and B (66), with co-infections of the two in two patients. Among the sequences obtained in this study, four multilocus genotypes (MLGs) of the sub-assemblage AII were observed within assemblage A. In contrast, 19 MLGs were detected within assemblage B due to the high sequence diversity at each locus. One MLG, however, was found in 51.9% (27/52) of assemblage B samples. Children were more commonly infected by assemblage B (44/53 or 83%) than adults (22/42 or 52.4%; χ² = 10.371, df = 1, P = 0.001). Asymptomatic infection was more common in patients with assemblage A (4/29 or 13.8%) than in those with assemblage B (1/66 or 1.5%; χ² = 6.091, df = 1, P = 0.029), and the frequency of abdominal pain occurrence was higher in assemblage B patients (65/66 or 98.5%) than assemblage A patients (25/29 or 86.2%; χ² = 6.091, df = 1, P = 0.029).

Conclusions: These results illustrate the existence of differences in genotype distribution between children and adults and clinical presentations between G. duodenalis genotypes. They are useful in understanding the transmission of G. duodenalis in humans in Spain.

Keywords: Assemblage; Giardia duodenalis; Multilocus genotyping; Spain.

Fig. 1

Cysts (a) and trophozoites (b) of Giardia duodenalis in a fecal sample and a duodenum biopsy of patients in Spain, respectively. The cysts were detected in microscopic analysis of wet mount of fecal material fixed with the merthiolate-iodine-formaldehyde solution under an Olympus BX43 using a 100× objective, while the trophozoites were detected by microscopic analysis of hematoxylin-eosin stained tissue section under an Olympus BX43 using a 60× objective. Scale-bars: 10 µm

Fig. 2

Genetic relationship of multilocus genotypes (MLGs) of Giardia duodenalis assemblage B based on eBURST analysis of sequences of the triosephosphate isomerase, β-giardin, and glutamate dehydrogenase genes. Each MLG is represented by a dot. The size of each dot is proportional to the number of samples with the MLG. The primary founder of the group is colored blue, while the subgroup founder is colored yellow. Single-locus variants are connected by lines. MLG-B15, MLG-B17 and MLG-B18 form singletons outside the main cluster