Enumerating genotypic diversity and host specificity of Giardia in wild rodents around a New York watershed

<i>Giardia</i> is a genus of flagellated protozoans that parasitize the gastrointestinal tract of humans and wildlife worldwide. While <i>G. duodenalis</i> is well-studied due to its potential to cause outbreaks of diarrheal illness in humans, other <i>Giardia</i> species from wildlife have been largely understudied. This study examines the occurrence, host specificity, and genotypic diversity of <i>Giardia</i> in wild rodents living within the New York City water supply watershed. A novel nested PCR assay targeting the 18S ssu-rDNA gene is introduced, which captures nearly the entire gene for improved species-level determination versus existing molecular typing methods. Molecular characterization of 55 <i>Giardia</i> specimens reveals at least seven novel lineages. Phylogenetic analysis indicates a close relationship between the newly characterized <i>Giardia</i> lineages and rodent hosts, suggesting rodents as important reservoirs of <i>Giardia</i> and its close relatives. These findings provide insights into the diversity of <i>Giardia</i> species and their public health potential in localities with human-wildlife interaction and further emphasizes the need for continued efforts to improve the molecular tools used to study microbial eukaryotes, especially those with zoonotic potential.