Filoviruses (Marburg and Ebola Viruses)

Two related African viruses are subsumed under the name filoviruses, Marburg and Ebola. These pathogens cause hemorrhagic fevers with high lethality rates. The few described Marburg virus outbreaks apparently in­volve monkey populations. Ebola outbreaks are apparently becoming more frequent. The natural reservoir of the filoviruses is unknown.

Diagnosis: by antigen assay, EM, and isolation.

Pathogen. The Marburg virus was isolated for the first time in 1967 as a result of three simultaneous outbreaks among laboratory staff in Marburg, Frank­furt, and Belgrade. The infection victims had been processing the organs of Cercopithecus(African green monkeys) from Uganda. Both the Marburg and Ebola viruses are threadlike, 14 im-long viral particles, in some cases branched and 80 nm thick in diameter. Their surface consists of an envelope of host-cell membrane with viral spikes. The genome consists of antisense- strand RNA in a helical nucleocapsid 50 nm in diameter.

Pathogenesis and clinical picture. The Marburg and Ebola viruses cause so-called hemorrhagic fevers. The clinical picture first manifests with fever, head­ache, and neck pain, conjunctivitis and diarrhea, followed by hepatic, renal, and CNS involvement and finally, as a result of consumption coagulopathy, leads to extensive hemorrhaging and terminal shock. In terms of the anatom­ical pathology, nearly all organs show hemorrhages and fibrin deposits.

Diagnosis. Only designated laboratories with special safety facilities can un­dertake isolation work on these viruses. Detection is either in blood with an electron microscope or using immunofluorescence on tissue specimens. The pathogens can be grown in cell cultures. Serodiagnosis is also possible.

Epidemiology and prevention. The reservoir of the Marburg and Ebola viruses is unknown. Subsequent to the Marburg outbreak in 1967 among lab personnel in Europe, Marburg viruses have only been found in Africa. The Ebola virus, named after a river in Zaire, has caused several outbreaks in Africa since 1976 in which lethality rates of 50-90% were observed. Im­ported Ebola infections have also been seen in monkey colonies in the USA and Italy.

Protective suits and vacuum-protected plastic tents are no longer recom­mended for healthcare workers in contact with Marburg and Ebola patients (as with Lassa fever), since interhuman transmission is by excretions (smear infection) and in blood, but not aerogenic. Despite this fact, the high level of infectivity of any aerosols from patient material must be kept in mind during laboratory work and autopsies.

References

Fritz H. Kayser, M.D. Emeritus Professor of Medical Microbiology Institute of Medical Microbiology, University of Zurich, Zurich, SwitzerlandThieme 2005, Stuttgart ! New York.