Ebola Biology

Ebola virus is the causative agent of Ebola hemorrhagic fever (EHF), a disease affecting humans and other primates. The incubation period for EHF is 2-21 days and typical early symptoms include fever, chills, malaise, and myalgia, followed by the onset of symptoms indicative of multi-organ stress and subsequent failure. The disease is also characterized by high death rates (as high as 90%) and worse yet, is highly contagious, spreading through direct contact with infected body fluids or skin/mucus membrane contact. This perfect storm of conditions make the possibility of a large-scale epidemic a very real concern.

Ebola virus and the related Marburg virus are members of the family Filoviridae, so named for their filamentous shape. Like other Filoviruses, Ebola is an enveloped, non-segmented, negative-stranded RNA virus. Ebola virus particles have at their core a viral nucleocapsid composed of a helical single stranded RNA genome wrapped around viral proteins NP, VP35, VP30, and L. The nucleocapsid is surrounded by an outer viral envelope studded with viral glycoprotein (GP) spikes, and viral proteins VP40 and VP24 sit between the nucleocapsid and the envelope.

The viral life cycle begins with host cell entry through a poorly understood mechanism. Once inside the viral RNA-dependent RNA polymerase (L) binds the 19 kb genome as a complex with other factors and transcribes the negative strand genome into a positive strand mRNA to be translated by the host cell's machinery. The seven genes are ordered in the genome as follows: 3-leader-NP-VP35-VP40-GP/sGP-VP30-VP24-L-trailer-5'. Once the concentration of nucleocapsid protein (NP) reaches a sufficient level, the RNA polymerase switches modes to genome replication, producing full-length positive strand genomes to be transcribed into negative orientation. These genomes self assemble with other virus proteins and bud from the host cell, sheathed in host cell membrane, thus completing the cycle.