Genetic Diversity of <i>Giardia duodenalis</i>: Multilocus Genotyping Reveals Zoonotic Potential between Clinical and Environmental Sources in a Metropolitan Region of Brazil

<div><p>Background</p><p><i>Giardia duodenalis</i> is a flagellate protozoan that parasitizes humans and several other mammals. Protozoan contamination has been regularly documented at important environmental sites, although most of these studies were performed at the species level. There is a lack of studies that correlate environmental contamination and clinical infections in the same region. The aim of this study is to evaluate the genetic diversity of a set of clinical and environmental samples and to use the obtained data to characterize the genetic profile of the distribution of <i>G. duodenalis</i> and the potential for zoonotic transmission in a metropolitan region of Brazil.</p><p>Methodology/Principal Findings</p><p>The genetic assemblages and subtypes of <i>G. duodenalis</i> isolates obtained from hospitals, a veterinary clinic, a day-care center and important environmental sites were determined via multilocus sequence-based genotyping using three unlinked gene loci. Cysts of <i>Giardia</i> were detected at all of the environmental sites. Mixed assemblages were detected in 25% of the total samples, and an elevated number of haplotypes was identified. The main haplotypes were shared among the groups, and new subtypes were identified at all loci. Ten multilocus genotypes were identified: 7 for assemblage A and 3 for assemblage B.</p><p>Conclusions/Significance</p><p>There is persistent <i>G. duodenalis</i> contamination at important environmental sites in the city. The identified mixed assemblages likely represent mixed infections, suggesting high endemicity of <i>Giardia</i> in these hosts. Most <i>Giardia</i> isolates obtained in this study displayed zoonotic potential. The high degree of genetic diversity in the isolates obtained from both clinical and environmental samples suggests that multiple sources of infection are likely responsible for the detected contamination events. The finding that many multilocus genotypes (MLGs) and haplotypes are shared by different groups suggests that these sources of infection may be related and indicates that there is a notable risk of human infection caused by <i>Giardia</i> in this region.</p>