In all epidemics, nosocomial transmission, via contaminated syringes or needles, was responsible for a significant number of deaths. In a small number of cases of the Zaire and Sudan strains, patients did not have contact with the blood or body fluids of other viremic patients. In these few cases, it is possible that the patients contracted the virus via aerosol transmission. Although the Zaire and Sudan strains are not usually passed from human to human by aerosol, the Reston strain is transmitted via small-particle aerosol between monkeys and from monkeys to humans. In addition, Ebola Zaire and Marburg virus have been isolated from the alveoli of infected monkeys.
Viruses can persist in injection equipment, multidose medicine vials, or in dried material.
The virus can also continue to be shed in the patient's semen for 3 or 4 months after symptoms disappear. In one case, the virus has isolated from the anterior chamber fluid of a uveitis patient. The exact mechanism is unknown. Systemically, the virus involves the heart, blood vessels, stomach, intestine, liver, lymphoid organs, and kidneys, causing hemorrhaging and in many cases, organ failure. The host usually dies with no evidence of an immune response.