Phylogeny of coccidian parasites (Eimeriorina, Apicomplexa) infecting shrews

Despite their ecological importance and protected status, the diversity, host associations, and evolutionary relationships of coccidia infecting shrews (Eulipotyphla: Soricidae) remain poorly understood. In particular, the extent of host specificity, the occurrence of host-switching events, and the relationships among coccidian lineages infecting different shrew hosts remain unclear. Here, we investigated coccidian diversity and phylogenetic relationships across several shrew genera and species to clarify parasite-host associations and provide new insights into the evolutionary processes shaping coccidian diversity in shrews. Fecal samples from 188 shrews representing the genera Crocidura, Neomys, Sorex, and Suncus, collected across multiple localities in Europe and two localities in Asia, were examined. Coccidia were detected in one quarter of the samples, generally at low intensities. Phylogenetic analyses based on partial COX1, COX3, and 18S rRNA sequences identified four distinct clusters: three were host-specific (two associated with Crocidura and one with Neomys), whereas one lineage was shared among Crocidura, Neomys, and Sorex. Two Isospora sequences from Sorex araneus clustered with isosporans previously reported from moles. No clear geographic structuring was observed, and the phylogenetic structure also did not mirror the observed morphological characters. The results indicate that host switching and subsequent repeated dispersal occur in eimerians of shrews, suggesting that these processes may be more widespread across small-mammal hosts than previously recognized. The findings expand current knowledge on coccidian diversity in shrews and provide new insights into the host specificity, ecology, and evolutionary dynamics of the parasitic protists.