A method of reducing the risk of filovirus hemorrhagic fever or a symptom thereof in a mammal host exposed to a filovirus (e.g., Ebola or Zika virus), comprising administering an effective amount of quercetin-3 β-O-D-glucoside (Q3G) or an analogue thereof, or a composition comprising Q3G or analogue thereof and a pharmaceutically acceptable carrier, to said host prior to said exposure.