Prevalence and molecular characterization of Strongyloides spp. in domestic and wild felids from Switzerland.

Strongyloides spp. infecting felids remain largely understudied. To date, four Strongyloides species have been reported in felids worldwide: S. felis, S. planiceps, S. stercoralis, and S. tumefaciens. Most epidemiological studies performed in felids identified the parasites only to genus level. This study aimed to determine the prevalence of Strongyloides spp. in domestic cats (Felis catus), free-ranging Eurasian lynx (Lynx lynx), and European wildcats (Felis silvestris) from Switzerland, while providing detailed morphological and molecular characterization of the parasites. A total of 490 intestinal content and faecal samples (172 domestic cats, 261 lynx, and 57 wildcats) were analysed using Baermann and sedimentation-flotation techniques. Morphological measurements of Strongyloides spp. eggs, larvae and adults were recorded. Molecular identification involved conventional PCRs targeting the 18S rRNA and cox1 gene fragments, followed by Sanger sequencing, Oxford Nanopore Technologies (ONT) deep amplicon sequencing and bioinformatic analysis. The coproscopical prevalence of Strongyloides spp. in wild felids was 9.6% (25/261) in lynx and 7% (4/57) in wildcats, whereas in domestic cats it was 0.6% (1/172). All positive samples contained free first-stage rhabditiform larvae. Eight lynx samples additionally had larvated eggs and in three lynx and one wildcat, also rhabditiform adults were present. Morphological features were consistent with S. planiceps. Sanger sequencing mostly failed. ONT sequencing and phylogeny confirmed S. planiceps in 16 representative samples (12 lynx, three wildcats, one domestic cat) and revealed high intraspecific variability in the cox1 gene. Additionally, S. ratti sequences were detected in one wildcat. This study represents the first prevalence study with molecular characterization in wild felid populations globally, and the first identification of S. planiceps in Europe. A higher prevalence was observed in wild felids than in domestic pet cats. ONT deep amplicon sequencing proved to be a robust tool for identifying Strongyloides species from complex samples, overcoming the Sanger sequencing limitations.