Because the virus is contracted by aerosol dissemination, concern arose shortly after the first cases emerged in 1989 due to fear of biological warfare. Potential biological terrorism agents were identified and categorized in 1999 by the Centers for Disease Control and Prevention (CDC) as part of the Congressional initiative to further response capabilities to biological weapons. Arenaviruses causing hemorrhagic fevers, along with a genus of virus called filoviruses, were categorized in Category A; these are pathogens with the highest potential impact on public health safety.