Reverse genetics and comparative pathogenesis of Lone star virus.
Lone star virus (LSV) is a bandavirus first isolated from Amblyomma americanum ticks in the United States (U.S.) and is phylogenetically related to severe fever with thrombocytopenia syndrome virus (SFTSV), Heartland virus (HRTV), and Bhanja virus, each of which has been associated with severe human disease. In contrast to these better-characterized bandaviruses, LSV remains poorly studied, and its pathogenic potential is not well defined. Recent detection of LSV RNA in cerebrospinal fluid from an immunocompromised patient in Idaho, U.S., with fatal meningoencephalitis further highlights the need for experimental systems to investigate LSV biology. Here, we rescued recombinant (r) LSV from cloned cDNA and used it to characterize LSV. rLSV replicated similarly to the parental isolate in mammalian cells and caused rapid, systemic, and lethal disease in IFNAR-/- mice, with widespread detection of viral (v) RNA across multiple tissues, hepatic and splenic pathology, and induction of inflammatory cytokines. In contrast, C57BL/6J mice controlled infection and exhibited no clinical disease. To place LSV within a broader comparative framework, we generated rSFTSV from cloned cDNA and compared rLSV, rSFTSV, and HRTV in cell culture and IFNAR-/- mice. Our studies revealed distinct disease kinetics among these related tick-borne bandaviruses and showed that HRTV-induced immunity protected against homologous HRTV rechallenge and heterologous rSFTSV challenge, but not rLSV challenge. Together, these findings establish reverse-genetics platforms and small-animal models for comparative bandavirus studies, define key features of LSV pathogenesis, and place this neglected virus within a framework of related bandaviruses that differ in virulence and immunological overlap. ImportanceTick-borne bandaviruses include several viruses associated with severe human disease, yet many related viruses remain poorly characterized. Lone star virus (LSV) was first isolated from Amblyomma americanum ticks decades ago, but experimental tools and animal models to study LSV infection have been lacking. Here, we generated a recombinant LSV and used it to define the outcome of infection in immunocompromised and immunocompetent mice. We show that LSV can cause rapid, systemic, and lethal disease when type I interferon signaling is absent, whereas immunocompetent mice restrict infection and remain clinically normal. By comparing LSV with Heartland virus and severe fever with thrombocytopenia syndrome virus, we also show that related tick-borne bandaviruses differ in disease kinetics and immune protection. These findings provide foundational tools for studying LSV and highlight the importance of experimentally characterizing neglected tick-borne viruses before their pathogenic potential is fully understood.