filovirus, any virus belonging to the family Filoviridae. Filoviruses have enveloped virions (virus particles) appearing as variably elongated filaments that are about 80 nm (1 nm = 10−9 metre) in diameter and generally between 650 and 1,400 nm in length. The virions are pleomorphic (varying in shape) and contain a helical nucleocapsid, which consists of a protein shell, or capsid, and contains the viral nucleic acids. The filovirus genome is made up of a single strand of negative-sense RNA (ribonucleic acid), about 19 kilobases in length, and an endogenous RNA polymerase. The lipoprotein envelope of the virion contains a single type of glycoprotein, which projects from the virion surface and serves as the antigen that binds to receptors on host cells, thereby facilitating the process of viral infection. (Antigens are foreign proteins capable of stimulating an immune response in infected organisms.)
Filoviridae consists of two genera, Marburgvirus and Ebolavirus. The first strain of Marburgvirus was discovered in 1967, when it was transported with imported monkeys to Marburg, Germany, and caused a fatal outbreak. The first strain of Ebolavirus was discovered in 1976, taking its name from the Ebola River in the northern Congo basin of Central Africa, where it first appeared. Type species include the Marburg type Lake Victoria marburgvirus and the Ebola type Zaire ebolavirus. Four other Ebola species have been characterized: Reston ebolavirus, Sudan ebolavirus, Taï Forest ebolavirus, and Bundibugyo ebolavirus.
Filoviruses are confined primarily to regions of central, eastern, and western Africa. They are among the most dangerous human pathogens known, causing highly fatal hemorrhagic fevers; some strains of Ebolavirus cause death in 50 to 90 percent of victims. The filoviruses may also cause disease in primates.
The origin of filovirus epidemics remains unclear. Marburg and Ebola strains have been found in different species of fruit bats. Marburgvirus has been isolated from the Old World fruit bat Rousettus aegyptiacus, which lives in areas throughout sub-Saharan Africa. This species is suspected to serve as a reservoir for the virus and may be responsible for outbreaks of Marburg disease in humans.