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.
