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In the summer of 1976,

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a mysterious epidemic
suddenly struck two central African towns,

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killing the majority of its victims.

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Medical researchers suspected

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the deadly Marburg virus 
to be the culprit.

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But what they saw in microscope images
was an entirely new pathogen,

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which would be named after 
the nearby Ebola river.

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Like yellow fever or dengue,

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the disease caused by the Ebola virus
is a severe type of hemorrhagic fever.

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It begins by attacking 
the immune system's cells

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and neutralizing its responses,

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allowing the virus to proliferate.

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Starting anywhere from two 
to twenty days after contraction,

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initial symptoms like high temperature,

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aching,

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and sore throat

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resemble those of a typical flu,

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but quickly escalate to vomiting,

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rashes,

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and diarrhea.

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And as the virus spreads,

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it invades the lymph nodes 
and vital organs,

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such as kidneys and liver,
causing them to lose function.

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But the virus itself 
is not what kills Ebola victims.

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Instead, the mounting cell deaths 
trigger an immune system overload,

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known as a cytokine storm,

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an explosion of immune responses
that damages blood vessels,

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causing both internal 
and external bleeding.

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The excessive fluid loss 
and resulting complications

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can be fatal within six to sixteen days
of the first symptoms,

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though proper care and rehydration therapy

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can significantly reduce 
mortality rates in patients.

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Fortunately, 
while Ebola is highly virulent,

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several factors limit its contagiousness.

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Unlike viruses that proliferate through
small, air-born particles,

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Ebola only exists in bodily fluids,

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such as saliva,

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blood,

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mucus,

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vomit,

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or feces.

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In order to spread,

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these must be transmitted from 
an infected person into another's body

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through passageways such as the eyes,
mouth, or nose.

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And because the disease's severity

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increases directly along 
with the viral load,

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even an infected person 
is unlikely to be contagious

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until they have begun to show symptoms.

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While Ebola has been shown 
to survive on surfaces for several hours,

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and transmission through sneezing
or coughing is theoretically possible,

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virtually all known cases of contraction
have been through direct contact

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with the severely ill,

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with the greatest risk 
posed to medical workers,

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and friends or relatives of the victims.

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This is why despite 
its horrifying effects,

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Ebola has been far less deadly overall
than more common infections,

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such as measles,

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malaria,

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or even influenza.

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Once an outbreak has been contained,

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the virus does not exist 
in the human population

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until the next outbreak begins.

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But while this is 
undoubtably a good thing,

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it also makes Ebola difficult to study.

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Scientists believe fruit bats 
to be its natural carriers,

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but just how it is transmitted to humans
remains unknown.

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Furthermore, many of the countries 
where Ebola outbreaks occur

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suffer from poor infrastructure 
and sanitation,

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which enables the disease to spread.

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And the poverty of these regions,

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combined with the relatively low amount
of overall cases

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means there is little economic incentive
for drug companies to invest in research.

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Though some experimental medicines
have shown promise,

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and governments are funding development
of a vaccine,

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as of 2014,

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the only widespread and effective 
solutions to an Ebola outbreak remain

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isolation,

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sanitation,

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and information.