Istmiophora melis is a fluke species that is distributed in Europe, Asia, and North America. There, the adult worms parasitize the intestines of various vertebrates, including humans. Within its life cycle, this parasite utilizes two intermediate hosts. The first intermediate host is the great pond snail Lymnaea stagnalis, while various species of amphibians and freshwater fish serve as the second intermediate host (Radev et al., 2009). Typically, the infection with flukes occurs through the oral ingestion of the larval stage (Caspary et al., 2006).

Human Pathogenicity: Infection with the fluke Istmiophora melis in humans leads to an increase in eosinophilic granulocytes in the blood (eosinophilia) (Dönges, 1967).