Insights into Campula oblonga (Digenea: Brachycladiidae): Morphological, phylogenetic, and pathological studies in narrow-ridged finless porpoise (Neophocaena asiaeorientalis) from Korean waters

초록

Various marine parasites exploit marine mammals as definitive hosts; however, comprehensive parasitological studies remain lacking because of the inherent challenges in host sampling. This study aimed to investigate the pathological effects of Campula oblonga on the hepatobiliary system of the narrow-ridged finless porpoise (Neophocaena asiaeorientalis). We detected a digenean species, C. oblonga, in the hepatobiliary systems of 143 out of 196 (72.96 %) narrow-ridged finless porpoises stranded, bycaught or drifting along the Korean coastline between 2016 and 2024. The morphological analysis confirmed the characteristics of C. oblonga. Phylogenetic analyses based on partial mitochondrial DNA NADH dehydrogenase subunit 3 and large subunit rRNA regions supported previous findings, underscoring the need for a more in-depth genetic characterization of the family Brachycladiidae, a significant digenean group in marine mammals. Gross evaluation revealed hepatic nodules, irregular thickening of the bile duct walls, and signs of cholestasis due to physical obstruction by trematodes. These lesions were observed exclusively in the livers of individuals infected with C. oblonga and were absent in uninfected animals. In some cases, abscess-like lesions and pus-like material within the bile ducts were noted macroscopically, although histologic evidence of suppurative inflammation was lacking. Histopathological examinations identified bile duct dilatation accompanied by granulomatous cholangitis with periductal fibrosis, as well as hepatic granulomas centered on trematode parasites and eggs, surrounded by fibrous connective tissue. These lesions corresponded to grossly observed hepatic nodules and bile duct wall thickening, reflecting chronic inflammatory responses to trematode infection. This study represents the first report of pathological lesions caused by C. oblonga in narrow-ridged finless porpoises and highlights the significance of further investigation involving additional host species to enhance the understanding of this taxonomic group.

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