Polyparasitism in Two-Stranded Dolphins: Multisystem Pathological Alterations and Cellular Responses

Polyparasitism is frequently documented in cetaceans; however, the pathological consequences of concurrent multispecies helminth infections and their associated tissue responses remain incompletely understood. This study characterized multispecies helminth infections in two live-stranded dolphins from the Andaman coast of Thailand, a spinner dolphin (Stenella longirostris) and a pantropical spotted dolphin (Stenella attenuata), using integrated postmortem, parasitological, molecular, histopathological, and immunohistochemical approaches. Both dolphins harbored helminths involving multiple organ systems. Pulmonary nematodes were identified as Halocercus delphini, while larval and intestinal cestodes were identified as Clistobothrium sp. and Tetrabothrius sp., respectively. The most prominent pathological alterations occurred in the respiratory tract and included chronic pyogranulomatous bronchopneumonia, airway epithelial injury, fibrosis, and pulmonary congestion associated with Halocercus infection. Additional parasite-associated lesions included chronic enteritis, cholangitis with biliary epithelial injury and ductular reaction, pancreatic inflammation, and localized inflammatory responses surrounding larval cestode cysts in the blubber and testis. Immunohistochemistry demonstrated extensive interleukin-4 (IL-4) immunoreactivity in affected pulmonary and intestinal tissues, whereas interleukin-10 (IL-10) was undetectable. Nitrotyrosine and heat shock protein 70 (HSP70) immunoreactivity were widely distributed across parasite-associated tissues, while caspase-3 immunoreactivity showed tissue-dependent patterns. Collectively, these findings demonstrate that multispecies helminth infections in stranded dolphins were associated with multisystem pathological alterations accompanied by inflammatory, oxidative/nitrosative stress, cellular stress, and apoptotic responses. These findings highlight the potential pathological significance of polyparasitism in stranded dolphins and support consideration of parasite burden and associated tissue responses during cetacean postmortem investigations.