Genotypic and neuropathological characterization of Toxoplasma gondii in striped dolphins (Stenella coeruleoalba) stranded along the coasts of Southern Italy.

Toxoplasma gondii is an emerging cause of neurologic disease in cetaceans. In the present study, we combined molecular detection, microsatellite genotyping, and neuropathology in stranded striped dolphins along the coasts of Campania and Calabria (Southern Italy). During the years 2018-2023, 93 cetaceans were necropsied. Brain tissues were screened for T. gondii DNA by Real-Time PCR targeting the 529-bp repeat element; positive samples (Ct range 21-30) were genotyped using eight microsatellite markers (TUB2, W35, TgM-A, B18, B17, M33, IV.1 and XI.1) and compared with reference strains by hierarchical clustering. Histology and immunohistochemistry (IHC) for T. gondii were performed on available brains. T. gondii DNA in the brain was detected in 12/93 cetaceans; all positive cases were striped dolphins (Stenella coeruleoalba). Genotyping revealed two genotypes, with GII in 10/12 dolphins and GIII in 2/12. In 10 evaluable cases, lesions ranged from mild non-suppurative meningitis/meningoencephalitis to severe necrotizing encephalitis. IHC was positive in 7/10 positive cases; tissue cysts were observed in proximity to lesions in the more severely affected brains. These findings document the circulation of multiple T. gondii genotypes in pelagic dolphins from Southern Italy, supporting the land-to-sea transmission hypothesis and confirming the value of striped dolphins as sentinels of terrestrial pathogens from a One Health perspective.