Trematodes in the family Echinostomatidae (Looss, 1899) are globally distributed parasites of both humans and wildlife. In North America, echinostomes are nearly ubiquitous in freshwater systems, where they commonly parasitize snails as their first intermediate hosts, aquatic hosts such as snails or tadpoles as second intermediate hosts, and waterfowl and semi-aquatic mammals as their definitive hosts. Our study expands on sampling efforts in the midwestern United States and contributes novel ND1, ITS2, and 28S sequences from 12 lineages of echinostomes in the genera Echinostoma, Echinoparyphium, and Hypoderaeum. Additionally, COI barcoding and phylogenetic analysis of snail first intermediate hosts elucidated novel host-parasite combinations. Finally, we demonstrate that echinostomes are often not specific to 1 species of snail first intermediate host but rather to a family of aquatic snails, and we suggest that first intermediate hosts may drive echinostome speciation.
Schumacher et al. (2026) studied this question.