Transcriptomic plasticity in hybrid schistosomes can contribute to their zoonotic potential.

Hybrids between Schistosoma haematobium and Schistosoma bovis contribute to human and animal infections, highlighting complex interspecies interactions that facilitate schistosomiasis transmission. Schistosoma bovis infects multiple ruminant hosts, promoting cross-species transmission and increasing zoonotic risk. This study explores transcriptomic plasticity as a mechanism enabling hybrid schistosomes to adapt to different definitive hosts. We analysed two contexts: (1) introgressed S. haematobium × S. bovis hybrids, which exhibited higher virulence in sheep than parental S. bovis; and (2) S. bovis infecting different mammalian hosts. Introgression, the transfer of genetic material between species through hybridization and repeated backcrossing, was associated with 366 differentially expressed genes (4% of coding genes) between introgressed hybrids and S. bovis in sheep. Additionally, S. bovis showed host-dependent transcriptomic changes, with 30% of genes differentially expressed between infections in hamsters and sheep. Enriched biological processes shared across introgression and host adaptation included nuclear mRNA catabolism and inner mitochondrial membrane organization, indicating increased gene expression plasticity and metabolic adaptation to environmental stress. These findings suggest that transcriptomic plasticity enhances the adaptability of S. bovis and hybrid worms, increasing their zoonotic potential. This raises concerns for schistosomiasis control, as such plasticity could expand transmission capacity and complicate intervention strategies. This article is part of the Royal Society Science+ meeting issue 'Parasite evolution and impact in action: exploring the importance and control of hybrid schistosomes in Africa and beyond'.