Gastric lesions in dolphins stranded along the Eastern Adriatic coast

Stranded cetaceans are often found with gastric lesions associated with the presence of parasites; most frequently, nematodes of the genus Anisakis and the heterophyd digenean trematode Pholeter gastrophilus. In this study, we present histopathology mainly (but not exclusively) related to these 2 parasite species. Macroscopically, lesions associated with the presence of Anisakis spp. were characterised by the presence of ulcers within the gastric mucosa, while the digenean P. gastrophilus was found within large submucosal fibrotic nodules in the gastric wall. Anisakis-induced alterations included severe ulcerative gastritis with mixed inflammatory infiltrate often associated with colonies of bacteria, and mild to moderate granulomatous gastritis with eosinophilic infiltrate. P. gastrophilus-associated lesions were characterised by fibrogranulomatous gastritis with mixed inflammatory infiltrate. Additionally, immunohistochemical (IHC) analysis of P. gastrophilus lesions was consistent with the histopathologic findings, revealing inflammation-mediated stimulation. IHC-positive localisation of CD3+, iNOS+ and caspase-3+ cells suggests intensive accumulation of cytotoxic T-cells, proinflammatory cytokines and execution-phase of cell apoptosis at the parasitized area. In contrast, mechanical damage, rather than visible inflammatory response could be observed at the site of attachment of Braunina cordiformis recorded in 4 animals. Lesions not associated with the presence of parasites were mostly characterised by focal loss of superficial epithelial cells and accumulation of brown hemosiderin-like pigment or fibrous gastritis with lymphoplasmacytic infiltrate. In light of these results, we argue that observed 'tolerant' host-parasite interactions that led toward gastric lesions do not represent the cause of death and stranding of cetaceans included in this study.