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  • In the summer of 1976,

  • a mysterious epidemic suddenly struck two central African towns,

  • killing the majority of its victims.

  • Medical researchers suspected

  • the deadly Marburg virus to be the culprit.

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

  • which would be named after the nearby Ebola river.

  • Like yellow fever or dengue,

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

  • It begins by attacking the immune system's cells

  • and neutralizing its responses,

  • allowing the virus to proliferate.

  • Starting anywhere from two to twenty days after contraction,

  • initial symptoms like high temperature,

  • aching,

  • and sore throat,

  • resemble those of a typical flu,

  • but quickly escalate to vomiting,

  • rashes,

  • and diarrhea.

  • And as the virus spreads,

  • it invades the lymph nodes and vital organs,

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

  • But the virus itself is not what kills Ebola victims.

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

  • known as a cytokine storm,

  • an explosion of immune responses that damages blood vessels,

  • causing both internal and external bleeding.

  • The excessive fluid loss and resulting complications

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

  • though proper care and rehydration therapy

  • can significantly reduce mortality rates in patients.

  • Fortunately, while Ebola is highly virulent,

  • several factors limit its contagiousness.

  • Unlike viruses that proliferate through small, airborne particles,

  • Ebola only exists in bodily fluids,

  • such as saliva,

  • blood,

  • mucus,

  • vomit,

  • or feces.

  • in order to spread,

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

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

  • And because the disease's severity

  • increases directly along with the viral load,

  • even an infected person is unlikely to be contagious

  • until they have begun to show symptoms.

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

  • and transmission through sneezing or coughing is theoretically possible,

  • virtually all known cases of contraction have been through direct contact

  • with the severely ill,

  • with the greatest risk posed to medical workers

  • and friends or relatives of the victims.

  • This is why, despite its horrifying effects,

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

  • such as measles,

  • malaria,

  • or even influenza.

  • Once an outbreak has been contained,

  • the virus does not exist in the human population

  • until the next outbreak begins.

  • But while this is undoubtedly a good thing,

  • it also makes Ebola difficult to study.

  • Scientists believe fruit bats to be its natural carriers,

  • but just how it is transmitted to humans remains unknown.

  • Furthermore, many of the countries where Ebola outbreaks occur

  • suffer from poor infrastructure and sanitation,

  • which enables the disease to spread.

  • And the poverty of these regions,

  • combined with the relatively low amount of overall cases

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

  • Though some experimental medicines have shown promise,

  • and governments are funding development of a vaccine,

  • as of 2014,

  • the only widespread and effective solutions to an Ebola outbreak remain

  • isolation,

  • sanitation,

  • and information.

In the summer of 1976,

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B2 US TED-Ed ebola outbreak immune sanitation contraction

【TED-Ed】What we know (and don't know) about Ebola - Alex Gendler

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