On May 6, 1995, the U.S. Centers for Disease Control and Prevention (CDC) investigated an deadly outbreak of Ebola virus in Zaire. As of May 17, the investigation had identified 93 suspected cases of VHF in Zaire, of which 86 (92%) were fatal.

The natural reservoirs for these viruses are not known. Although nonhuman primates were involved in the 1967 Marburg outbreak, the 1989 U.S. outbreak, and the 1994 Cote d’Ivoire case, their role as virus reservoirs is unknown.

Although aerosol spread has not been documented among humans, this mode of transmission has been demonstrated among nonhuman primates.