Ebola Virus
The Ebola virus causes an acute, serious illness which is often
fatal if untreated. Ebola virus disease (EVD) first appeared in 1976 in 2
simultaneous outbreaks –Sudan and Democratic Republic of Congo. The latter
occurred in a village near the Ebola River, from which the disease takes its
name. The current outbreak in west Africa, (first cases notified in March
2014), is the largest and most complex Ebola outbreak since the Ebola virus was
first discovered in 1976.
EBOV carries a negative-sense RNA genome in virions that are
cylindrical/tubular, and contain viral envelope, matrix, and nucleocapsid components.
The overall cylinders are generally approx. 80 nm in diameter, and having a
virally encoded glycoprotein (GP) projecting as 7-10 nm long spikes from its
lipid bilayer surface. The cylinders are of variable length, typically 800 nm,
but sometimes up to 1000 nm long. The outer viral envelope of the virion is
derived by budding from domains of host cell membrane into which the GP spikes
have been inserted during their biosynthesis. Each virion contains one molecule
of linear, single-stranded, negative-sense RNA, 18,959 to 18,961 nucleotides in
length.
It is thought that fruit bats of the Pteropodidae family are
natural Ebola virus hosts. Ebola is introduced into the human population
through close contact with the blood, secretions, organs or other bodily fluids
of infected animals such as chimpanzees, gorillas, fruit bats, monkeys, forest
antelope and porcupines found ill or dead or in the rainforest. Ebola then
spreads through human-to-human transmission via direct contact (through broken
skin or mucous membranes) with the blood, secretions, organs or other bodily
fluids of infected people, and with surfaces and materials (e.g. bedding,
clothing) contaminated with these fluids.
The incubation period, that is, the time interval from infection
with the virus to onset of symptoms is 2 to 21 days. Humans are not infectious
until they develop symptoms. First symptoms are the sudden onset of fever
fatigue, muscle pain, headache and sore throat. This is followed by vomiting,
diarrhoea, rash, symptoms of impaired kidney and liver function, and in some
cases, both internal and external bleeding (e.g. oozing from the gums, blood in
the stools). Laboratory findings include low white blood cell and platelet
counts and elevated liver enzymes.
Supportive care-rehydration with oral or intravenous fluids- and
treatment of specific symptoms, improves survival. There is as yet no proven
treatment available for EVD. However, a range of potential treatments including
blood products, immune therapies and drug therapies are currently being
evaluated. No licensed vaccines are available yet, but 2 potential vaccines are
undergoing human safety testing.
