Bringing order to chaos: A new classification of avian schistosomes and their genetic lineages in the context of swimmer's itch.

Abstract

Schistosomes are parasitic flatworms that infect birds and mammals, including humans, using gastropods as intermediate hosts. Despite their ecological and medical importance, the taxonomy of avian schistosomes is poorly understood due to morphological similarity and patchy molecular data. Here, we present the global synthesis of avian schistosome diversity integrating all available sequence data for three genetic markers (cox1, ITS1-5.8S-ITS2 and 28S rDNA) with newly obtained samples from snails and birds across Europe. Among the markers, cox1 proved to be the most sensitive and reliable for species delimitation and is recommended as the primary barcode for future studies. We identified 25 molecularly confirmed species, representing 29% of the 85 nominal species worldwide, and a further 52 unnamed genetic lineages that may correspond to morphologically known but molecularly unconfirmed species or represent new species. In Europe, we have recognised seven named species and 12 genetic lineages, including six newly discovered lineages based on material obtained from our field collections. To facilitate uniform taxonomy and comparative research, we propose a standardised molecular framework for naming undescribed avian schistosome lineages. Although the morphology of avian schistosome cercariae offers limited taxonomic resolution due to high interspecific similarity, two distinct morphotypes were identified that generally correspond to infections in lymnaeid and planorbid snail hosts.