Digenean trematodes (Trematoda: Digenea) parasitizing the digestive system of the great cormorant (Phalacrocorax carbo) in Hungary

Great cormorants (Phalacrocorax carbo) are widespread piscivorous birds, which cause huge economic losses in the fish fauna worldwide. As a consequence of their predatory behaviour, they serve as definitive hosts for many digenean trematodes, and their digestive systems usually contain several parasite species.

Between 2019 and 2022, 131 bird carcasses were collected from Biharugra (Hungary) as culling on the cormorant population. Their digestive systems were subjected to parasitological examination. The studied organs (131 intestines, 44 stomachs and 21 pharynxes) were opened, and their contents were settled in water, filtered, and sorted under microscope. For species identification, sequence analysis of the ITS region was performed. Of the 131 birds, 118 were infected by tapeworms or nematodes, 105 with trematodes, and 10 were parasite-free.

The vast majority of obtained sequences (57 of the 105 trematodes) belonged to the genus Petasiger (43/57) and Hysteromorpha triloba (13/57). A single specimen of Metorchis sp. (1/57) as a zoonotic trematode was recorded during our survey. The results confirmed the high trematodes prevalence of the examined cormorants. However, most of them are not considered as human pathogens.