Objective: The source of infection or mode of transmission of Ebola virus to human index cases of Ebola fever has not been established. Field observations in outbreaks of Ebola fever indicate that secondary transmission of Ebola virus is linked to improper needle hygiene, direct contact with infected tissue or fluid samples, and close contact with infected patients. While it is presumed that the virus infects through either breaks in the skin or contact with mucous membranes, the only two routes of exposure that have been experimentally validated are parenteral inoculation and aerosol inhalation. Epidemiologic evidence suggests that aerosol exposure is not an important means of virus transmission in natural outbreaks of human Ebola fever; this study was designed to verify that Ebola virus could be effectively transmitted by oral or conjunctival exposure in nonhuman primates.
Materials and methods: Adult rhesus monkeys (Macaca mulatta) were exposed to Ebola-Zaire (Mayinga) virus orally (N=4), conjunctivally (N=4), or by intramuscular inoculation (N=1, virus-positive control).
Results: Four of four monkeys exposed by the conjunctival route, three of four monkeys exposed by the oral route, and the intramuscularly inoculated positive control monkey (one of one) were successfully infected with Ebola-Zaire (Mayinga). Seven monkeys died of Ebola fever between days 7 and 8 postexposure. One monkey was given aggressive supportive therapy and a platelet transfusion; it lived until day 12 postexposure.
Conclusions: Findings in this study experimentally confirm that Ebola virus can be effectively transmitted via the oral or conjunctival route of exposure in nonhuman primates.