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  • For most of human history,

  • medical workers sought to treat diseases or cure them.

  • The rise of vaccination in the 19th century

  • enhanced the potential to prevent people

  • from contracting illnesses in the first place.

  • But only in recent decades did it become possible

  • to ensure that a particular disease never threatens humanity again.

  • The story of smallpox,

  • the first and, so far, the only disease

  • to be permanently eradicated from the world,

  • shows how disease eradication can happen and why it is so difficult to achieve.

  • Smallpox emerged in human populations thousands of years ago

  • as a contagious virus that spread rapidly,

  • primarily through close, face to face contact,

  • causing fever, aches and rashes.

  • It killed up to 30% of its victims

  • and often left survivors with life-long disfiguring scars.

  • The devastating impact of smallpox was so great

  • that several cultures had religious deities specifically dedicated to it.

  • In the 20th century alone,

  • it is estimated to have killed more than 300 million people worldwide.

  • With the effective deployment of vaccination,

  • the number of cases began to decrease.

  • By seeking out infected individuals,

  • isolating them,

  • and vaccinating their contacts to prevent further transmission,

  • scientists realized that the spread of the disease could be haulted.

  • In fact, because smallpox could only survive in human hosts,

  • vaccinating all of an infected persons' potential contacts

  • would stop the virus dead in its tracks

  • and eliminate it from that region.

  • Once this strategy had succeeded

  • in ridding most industrialized countries from disease,

  • health officials realized that eradicating it worldwide was within reach.

  • But this was not an easy process,

  • proving especially difficult in places suffering from poor infrastructure

  • or civil wars.

  • The eradication effort took decades

  • and involved millions of people working together,

  • from world leaders and international organizations

  • to rural doctors and community workers.

  • In India, one of the last strongholds of the disease,

  • health workers visited every one of the country's 100 million households

  • to search for cases.

  • Through this unprecedented worldwide effort,

  • in which even rival superpowers cooperated,

  • smallpox was finally declared eradicated in 1980,

  • saving approximately 40 million lives over the following two decades.

  • There were several factors

  • that made smallpox an ideal candidate for eradication.

  • First, humans are essential to the smallpox lifecycle,

  • so breaking the chain of human to human transmission

  • causes the virus to die out.

  • In contrast, many other pathogens, like ebola or the bubonic plague,

  • can survive in animal carriers,

  • while the bacteria that cause tetanus can even live in the soil.

  • Secondly, individuals infected with smallpox

  • displayed a characteristic rash, making them easy to identify,

  • even without a lab test.

  • The lack of such practical diagnostic tools

  • for diseases with non-specific symptoms, or that have long incubation periods,

  • such as AIDS, makes their eradication more difficult.

  • Third, the availability of a smallpox vaccine

  • that provided immunity for five to ten years in a single dose

  • meant that there was an effective intervention

  • to stop the virus from spreading.

  • And finally, the initial success of several countries

  • in eliminating the disease within their borders

  • served as a proof of principle for its eradication worldwide.

  • Today, the same criteria are applied to determine

  • whether other diseases can be similarly eliminated.

  • And even though smallpox remains the only success story thus far,

  • several other pathogens may be next in line.

  • Great progress has been made towards eradicating guinea worm disease

  • simply by use of water filters.

  • And vaccination for polio,

  • which previously disabled hundreds of thousands of people each year

  • is estimated to have prevented 13 million cases of paralysis,

  • and 650,000 deaths since 1988.

  • With a 99% drop in infections since the eradication effort began,

  • one final push is all that is needed

  • to ensure that polio will never paralyze another child.

  • Disease eradication is one public health effort that benefits all of humanity

  • and challenges us to work together as a global community.

  • Beyond eliminating specific diseases,

  • eradication programs benefit local populations

  • by improving health infrastructure.

  • For example, Nigeria recently used facilities and personnel

  • from their polio eradication program to effectively control an ebola outbreak.

  • Further more, globalization and international travel

  • means that even a single infection anywhere in the world

  • can potentially spread to other regions.

  • By helping to protect others, we help to protect ourselves.

  • Disease eradication is the ultimate gift we can give to everyone alive today,

  • as well as all future generations of humanity.

For most of human history,

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TED-ED】天然痘から学ぶ。病気を根絶する方法-ジュリー・ガロンとウォルター・A・オーレンスタイン (【TED-Ed】Learning from smallpox: How to eradicate a disease - Julie Garon and Walter A. Orenstein)

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    稲葉白兎 に公開 2021 年 01 月 14 日
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