First Characterization and Zoonotic Potential Evaluation of <i>Giardia duodenalis</i> in Ferrets in China

<i>Giardia duodenalis</i> is a protozoan parasite that causes an important zoonosis in humans and a number of mammals, but has been poorly reported in ferrets. In the present study, we obtained a <i>G. duodenalis</i> isolate from a pet ferret and cultured it <i>in vitro</i>. The morphological character was consistent with <i>G. duodenalis</i>, being inverted pear-shaped with four pairs of flagella. The trophozoites measured 15.0 ± 1.2 μm (<i>n</i> = 50) in length and 7.5 ± 0.8 μm (<i>n</i> = 50) in width. The genome of the new isolate was 12.1 Mbp, which was relatively larger with a high guanine-cytosine (GC) content compared to <i>G. duodenalis</i> isolates from other hosts. 720 variant genes were identified, suggesting that the isolate might have evolved unique genetic features, potentially reflecting differences in its adaptive or pathogenic capabilities. The pathogenicity experiments revealed that the infection caused significant duodenal lesions, characterized by villous atrophy and breakage. Additionally, varying degrees of pathological changes were observed in other intestinal segments, and the infected animals exhibited a reduced rate of weight gain compared to the control group. In addition, molecular identification showed that the isolate belonged to zoonotic assemblage A at all three loci (<i>tpi</i>, <i>bg</i>, and <i>gdh</i>). Furthermore, the infection rate among 111 ferret fecal samples was 14.41%, with assemblage A as the dominant genotype. The sequence of <i>G. duodenalis</i> obtained from the genome of ferret feces in this study was more closely related to the Japanese isolates in East Asia in terms of phylogenetics and more distantly related to the German isolates in Europe. In conclusion, these findings suggested that <i>G. duodenalis</i> in ferrets exhibited high zoonotic potential, and the genomic and epidemiological data provided an important theoretical basis for future studies on the transmission and evolution of <i>G. duodenalis</i>.