Dermal-associated schistosomatoidean eggs exhibit a stronger multinucleated giant cell response than intravascular eggs in fibropapilloma tumors of juvenile green sea turtles (Chelonia mydas)

Schistosomatoidean trematodes are important parasites of sea turtles, and their eggs can embolize to multiple tissues and induce chronic granulomatous inflammation. Although schistosomatoidean eggs have occasionally been reported within fibropapilloma tumors, the influence of their tissue localization on the associated host response remains poorly understood. We characterized schistosomatoidean eggs and associated histopathological changes in fibropapillomas of juvenile green sea turtles ( Chelonia mydas ) from Guanabara Bay, Rio de Janeiro, Brazil, and investigated whether inflammatory responses differed between dermal-associated and intravascular eggs. Forty-nine turtles were captured during health monitoring, of which 30 (61.2%) had external fibropapillomas. Histopathological examination was performed on 42 tumor sections from 27 turtles. Schistosomatoidean eggs were detected in 28 sections (66.7%), representing 18 turtles, with 142 eggs identified. Based on histomorphological criteria complemented by von Willebrand factor immunohistochemistry, 87 eggs (61.3%) were classified as dermal-associated and 55 (38.7%) as intravascular. Eggs were frequently accompanied by epithelioid macrophages, lymphocytes, heterophils, Langhans-type multinucleated giant cells, fibroplasia, and disorganized collagen deposition. Generalized linear mixed models accounting for repeated observations within turtles showed that dermal-associated eggs had significantly greater odds of association with multinucleated giant cells than intravascular eggs (OR = 5.41, 95% CI: 2.46–11.90; p < 0.001). Egg localization was not significantly associated with fibrosis or pyogranulomatous inflammation. These findings demonstrate that schistosomatoidean eggs are frequent within fibropapilloma tissues in this population and indicate that their localization within the tumor influences specific components of the local host inflammatory response.