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  3. When Did Aids Begin? The yea

When Did Aids Begin? The yea

游客2023-12-25  7
问题                                                 When Did Aids Begin?
    The year was 1959. Location: the central African city of Leopoldville, now called Kinshasa, shortly before the waves of violent rebellion that followed the liberation of the Belgian Congo. A seemingly healthy man walked into a hospital clinic to give blood for a Western backed study of blood diseases. He walked away and was never heard from again. Doctors analyzed his sample, froze it in a test tube and forgot about it. A quarter century later, in the mid-1980s, researchers studying the growing AIDS epidemic took a second look at the blood and discovered that it contained HIV, the virus that causes AIDS.
    And not just any HIV. The Leopoldville sample is the oldest【C21】________of the AIDS virus ever isolated and may now help solve the【C22】________of how and when the virus made the leap from animals (moneys or chimpanzees) to【C23】________, according to a report published last week in Nature. Dr. David Ho,【C24】________of the Aaron Diamond AIDS Research Center in New York City and【C25】________of the study’s samples, says DNA pushes the putative origin of the AIDS【C26】________back at least a decade, to the early "50s over even the "40s.
    Over the【C27】________15 years, scientists have identified at least 10 subtypes of the【C28】________virus. But they couldn’t tell whether they were seeing【C29】________on one changeable virus or the handiwork of several【C30】________viruses that had made the jump from primates to man. A【C31】________look at the genetic mutations in the Leopoldville sample strongly【C32】________that all it took to launch the AIDS epidemic was one unlucky【C33】________of events.
    By comparing the DNA of the 1959 virus with that of【C34】________taken from the "80s and "90s, Ho and his【C35】________constructed a viral family tree in which the Leopoldville isolate sits right【C36】________the juncture where three subtypes branch out. The 39-year-old【C37】________is also strikingly similar to the other seven subtypes. The clear implication: all the viral【C38】________can be traced back to a single event or a closely related group of【C39】________. One theory is that AIDS started through contact with infected monkeys in a【C40】________area and spread to the rest of the population through urbanization and mass inoculations.
    The findings underscore how rapidly HIV can adapt to its surroundings, making it devilishly difficult to develop effective vaccines. No one knows how many more subtypes of HIV will sprout in the next 40 years, but chances are they will be every bit as lethal as the ones we see today, if not more so. [br] 【C25】
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