To determine the 90% lethal dose (LD90) of our HB29 virus stock, a small-scale titration of SFTSV in IFNAR-/- mice was performed to guide the design of the full-scale pathogenesis and pathophysiology study to assess vascular permeability, cytokine responses, viral replication and dissemination, and histopathology during the course of infection. The gene discussed is IFNAR1; the disease is infection.