Location. Asia and Africa. One particularly "fertile" area for Ebola is on the border of Kenya and Uganda, in the Mt. Elgon region. Visitors to the Kitum cave on top of Mt. Elgon have contracted Marburg, while Ebola has been isolated from monkeys in Uganda, within 60 miles of Mt. Elgon. Many residents of Central Africa (between 2% and 7% of the population tested) have antibodies to Ebola virus. People in the Haut-Ogooue region of Gabon are routinely exposed to Ebola.
It is possible that the virus has a wide geographic distribution in which monkeys are a significant factor--not as a reservoir, but possibly as a host species to an as-yet unknown arthropod vector. Studies have shown that 10% of all Asian and African monkeys tested carry Ebola antibodies.
[ Next topic ][ Top of file ]
Vector. The natural reservoir for Ebola is unknown. Epidemiologists have tested bats, monkeys, spiders and ticks for the virus, but have not been able to acquire definitive data. Common factors indicate that the natural reservoir is part of rural Africa, and CDC tests have shown that 10% of all Asian and African monkeys have antibodies to filoviruses. However, because the virus is as pathogenic in nonhuman primates as it is in humans, it is highly unlikely that monkeys themselves are a reservoir. It is speculated that persistent mammalian infection may help maintain the virus in nature, but that the natural reservoir is more likely to be a long-lived arthropod associated with the monkeys.
Secondary spread of the disease is via contact with infected persons or contact with blood, secretions, or excretions of infected persons. However, contact between viremic persons results in infection rates of approximately 10% ---such contact is not an efficient form of viral transmission. Infection via contact during the incubation period is rare. In contrast, nosocomial transmission is extremely dangerous. 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 ***** for 3 or 4 months after symptoms disappear. In one case, the virus was isolated from the anterior chamber fluid of a uveitis patient.
