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In the summer of 1976,

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a mysterious epidemic[br]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 [br]to be the culprit.

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

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which would be named[br]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[br]is a severe type of hemorrhagic fever.

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It begins by attacking [br]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[br]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 [br]and vital organs,

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

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But the virus itself [br]is not what kills Ebola victims.

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Instead, the mounting cell deaths [br]trigger an immune system overload,

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known as a cytokine storm,

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an explosion of immune responses[br]that damages blood vessels,

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causing both internal and external bleeding.

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The excessive fluid loss [br]and resulting complications

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

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though proper care and rehydration therapy

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can significantly reduce [br]mortality rates in patients.

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Fortunately, [br]while Ebola is highly virulent,

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several factors limit its contagiousness.

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Unlike viruses that proliferate through[br]small, airborne 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 [br]an infected person into another's body

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through passageways such as the eyes,[br]mouth, or nose.

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And because the disease's severity

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increases directly along [br]with the viral load,

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even an infected person [br]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 [br]to survive on surfaces for several hours,

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and transmission through sneezing[br]or coughing is theoretically possible,

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virtually all known cases of contraction[br]have been through direct contact

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with the severely ill,

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with the greatest risk [br]posed to medical workers

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and friends or relatives of the victims.

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This is why,[br]despite its horrifying effects,

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Ebola has been far less deadly overall[br]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 [br]in the human population

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until the next outbreak begins.

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But while this is undoubtedly a good thing,

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it also makes Ebola difficult to study.

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Scientists believe fruit bats [br]to be its natural carriers,

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but just how it is transmitted to humans[br]remains unknown.

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Furthermore, many of the countries [br]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[br]of overall cases

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

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Though some experimental medicines[br]have shown promise,

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and governments are funding development[br]of a vaccine,

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as of 2014,

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the only widespread and effective [br]solutions to an Ebola outbreak remain

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isolation,

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sanitation,

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and information.