A novel narnavirus attenuates stress resistance and fungal virulence in Talaromyces marneffei

Talaromyces marneffei is a lethal human pathogenic fungus endemic to Southeast Asia. While the previously reported mycovirus Talaromyces marneffei partitivirus 1 (TmPV1) enhances fungal virulence, we report the discovery of a second mycovirus, Talaromyces marneffei narnavirus 1 (TmNV1), which induces hypovirulence. Through viral curing experiments, we demonstrated that TmNV1 acted as a key virulence attenuator. Specifically, the TmNV1-infected strain exhibited increased sensitivity to Congo red and increased susceptibility to macrophage killing compared to the isogenic virus-free strain. In a murine model, infection with the TmNV1-infected strain resulted in significantly improved survival rates, reduced fungal burden, and attenuated inflammation. Interestingly, TmPV1 was found to synergistically amplify most of the hypovirulent effects associated with TmNV1. Cell wall remodelling, abnormal vacuole dynamics, and altered intracellular reactive oxygen species (ROS) production in macrophages were observed in TmNV1-/TmNV1-TmPV1-infected strains, which may be associated with their hypovirulent effects. Collectively, our findings provide new insights into the viral determinants of T. marneffei pathogenesis and reveal a critical virus-virus interaction within this important human fungal pathogen.