Habitat-associated detection of Toxoplasma gondii and Sarcocystis spp. in Cetaceans from the Brazilian coast.

Cetaceans are sentinels of marine ecosystem health and are increasingly exposed to protozoal pathogens. This study investigated the occurrence and molecular identity of Sarcocystidae protozoa in 159 stranded cetaceans representing 21 species along the Brazilian coast. Molecular analysis based on PCR amplification and sequencing of the sarcocystid internal transcribed spacer 1 (ITS1) region revealed infections in 14 individuals, showing a clear habitat-associated distribution. Toxoplasma gondii and Sarcocystis neurona were detected in nine coastal cetaceans, consistent with transmission from terrestrial definitive hosts via land-to-sea runoff. In contrast, a distinct Sarcocystis lineage consistently reported in cetaceans and pinnipeds was identified in six pelagic individuals. Analyses of mitochondrial cytochrome c oxidase subunit I and 18S rDNA markers revealed close similarity to species reported in avian definitive hosts, suggesting a life cycle involving marine or pelagic birds. This ecological segregation reflects differences in parasite transmission pathways and host-habitat interactions. This study provides the first report of S. neurona in Brazilian cetaceans and the first global record of this parasite in Guiana dolphin (Sotalia guianensis). Overall, these findings emphasize the role of habitat use in shaping infection patterns and reinforce the importance of a One Health framework to understand land-sea and potentially marine-specific pathogen transmission, as well as its implications for marine wildlife health and conservation.