Filoviruses: Marburg and Ebola Viruses

FILOVIRUSES: MARBURG AND EBOLA VIRUSES

The association of the Marburg virus with serious disease did not become apparent until 1967, when 26 cases of hemorrhagic fever occurred among persons in Germany and Yu-goslavia who were handling a group of African monkeys imported from central Uganda. The agent was later identified as Marburg virus and was apparently transmitted by the in-fected monkeys. In 1975 the virus was associated with a similar disease in three travelers in South Africa, and in 1980 in Kenya.

In 1976, severe outbreaks of hemorrhagic fever occurred in northern Zaire and south-ern Sudan, with case fatality rates from 50 to 90%. The illnesses were similar to those de-scribed for Marburg virus but were later shown to be caused by an antigenically different agent known as Ebola virus, named after a river in Zaire. More recently, another filovirus serologically related to Ebola virus was isolated from monkeys during an epizootic of simian hemorrhagic fever at a US quarantine facility. The reservoir was determined to be monkeys imported from the Philippines.

The reasons why these viruses can cause such fulminant, lethal hemorrhagic disease with shock in humans are not entirely clear. There is evidence that Marburg virus repli-cates in vascular endothelial cells, with subsequent necrosis. Other researchers have also shown that Ebola virus may exert its effects via a glycoprotein, synthesized in either a secreted or transmembrane form. The secreted glycoprotein interacts with neutrophils to inhibit early activation of the inflammatory response, while the transmembrane glycopro-tein binds to endothelial cells. Ebola virus produces disease in humans and subhuman primates; onset is within 4 to 6 days of inoculation. The reservoir, although uncertain, is thought to be in small mammals, perhaps rodents. Serosurveys of humans residing in the areas where outbreaks have occurred suggest that human infections may be relatively common; as much as 7% of the survey group had antibodies, indicating past infection. In symptomatic infections, the mortality for both Marburg and Ebola viruses is extremely high (30 to 80%).

As with the arenavirus-associated hemorrhagic fevers, the diagnosis of infection by these agents is suggested by a similar syndrome and recent travel history. Person-to-person transmission similar to that described for Lassa fever occurs in Ebola virus infections and may be possible with Marburg virus. Diagnosis can be confirmed in a reference center by isolation of virus, as well as by serologic methods employing indirect immunofluorescence or EIA. However, as with the arenavirus-associated hemorrhagic fevers, utmost care in iso-lation precautions and prompt notification of public health authorities are mandatory for suspected cases before any diagnostic attempts are made. There is no specific therapy for the infections.