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  3. Origins of a Plague Some gaybashers believe it is God’s way of punishing homosexuals(同性恋). Some Africans suspect it is just

Origins of a Plague Some gaybashers believe it is God’s way of punishing homosexuals(同性恋). Some Africans suspect it is just

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问题                               Origins of a Plague
    Some gaybashers believe it is God’s way of punishing homosexuals(同性恋). Some Africans suspect it is just another of the white man’s weapons of genocide(种族灭绝). Others have suggested that it was hatched in a biologicalweapons laboratory. There has been no shortage of theories about the origins of the virus that caused the current worldwide AIDS epidemic, but most have ranged from truly bizarre to scientifically implausible at best.
    Scientists were drawn into the battle earlier this month, when an article in Rolling Stone magazine contended that the AIDS epidemic was sparked 30 years ago by a polio (小儿麻痹症) vaccine(疫苗), which was accidentally contaminated with a monkey virus. The controversial idea had been completely dismissed by most scientists as simplistic and unprovable, but it does reveal one major point of consensus: African monkeys are almost certainly the source of the deadly virus. Just how the virus made the leap from its simian(猴类的) host to people is still being hotly debated, however, and the more likely explanations are far more complex, involving shifts in African society that turned an isolated disease into a plague.
    The polio vaccine theory was actually first proposed in a 1988 editorial in Child and Family, by Herbert Ratner, a former public health officer in Illinois. But the story begins in the mid1950s with Hilary Koprowski, former director of the Wistar Institute in Philadelphis, who, like his colleagues Jonas Salk and Albert Sabin, was racing to produce the vaccine that would protect the world against the scourge(折磨) of polio.
    According to the scenario painted in Rolling Stone, batches of Koprowski’s vaccine were inadvertently(不小心地) contaminated with a simian AIDS virus. Unlike Salk’s vaccine, which contained polio virus that had been killed with formaldehyde, Koprowski and Sabin created their vaccines from a weakened strain of polio virus that would invoke immunity but was too weak to cause disease. Sabin and Koprowski manufactured their vaccines by culturing this weakened strain of polio virus on monkey, kidneys, a fertile medium for the microbe(微生物) and supposedly the source of the simian AIDS virus, now called SIV.
    Such accidental contamination is not as farfetched as it might seem. Between 1954 and 1963, an estimated 10 million to 30 million Americans were inadvertently infected with SV40, an apparently harmless monkey virus borne as a silent passenger by both Salk’s and Sabin’s polio vaccines. SV40 was not discovered until 1961, and the U.S. Food and Drug Administration has since acted to ensure against similar contamination. Vaccine cultures are now carefully screened for all manner of viral contaminations.
    Nor is it implausible that human AIDS came from monkey. Researchers got their first hint of this possibility in the mid1980s, when it was discovered that a group of Asian monkeys used for biomedical research had fallen ill with a virus picked up from other monkeys caught from Africa. The germ turned out to be SIV, and subsequent research showed that in the wild at least six species of African monkeys carry their own strain of the virus. It does not make the African monkeys sick, but it proved deadly to Asian monkeys.
    Though researchers initially resisted the idea that human AIDS also came from African monkeys, that fact now seems wellestablished. Later last year, molecular(分子) virologists Beatrice Hahn and George Shaw of the University of Alabama presented convincing evidence that the simian virus. that infects sooty(似煤烟般黑的) mangabey, a type of monkey found in West Africa, carries virtually the same genetic material as HIV2, one of the two strains of human AIDS virus. This finding, says Shaw, provides direct evidence that AIDS originated in monkeys.
    If the AIDS virus did infect humans through a polio vaccine, Koprowski’s is the most likely candidate. The Sabin vaccine was given most often on a sugar cube, and the delicate virus could never have survived the exposure to air and stomach acid. But Koprowski’s vaccine was squirted(喷射) into people’s mouths, a method that could theoretically give the AIDS virus time to enter the bloodstream through cuts in the mouth. Moreover, Koprowski tested his vaccine on a huge number of people: at least 200 000 rural Africans in 1957, most of them in what was then known as the Belgian Congo, which is precisely the region of Africa where the rates of AIDS infection are soaring.
    While scientists concede the idea is conceivable, they want scientific proof, and evidence from one experiment already completed weakens the theory rather than strengthening it. Five years ago, Gerald Quinnan, a virologist with the Food and Drug Administration, tried repeatedly to get simian AIDS virus to grow in monkey kidney cells under the same conditions used to culture the polio virus; every attempt failed.
    To completely dismiss or confirm the theory, however, scientists say that the original vaccine should be tested for the presence of the AIDS virus, providing any vials(小药瓶) of it survived. But while Rolling Stone reports that Koprowski said there were vials in the freezer at Wisar Institute, the institute denies it.
    The polio vaccine theory is certainly not the first attempt to ex plain the origin of AIDS, nor is it the oddest. Last fall, a British clinician unearthed records of experiments conducted between 1922and 1966, in which researchers injected chimpanzee and monkey blood into approximately 40 human volunteers in and effort to immunize them against malaria. Unfortunately, no records exist to track down the volunteers, and no blood samples remain to check for the simian AIDS virus.
    The most compelling explanation f6r the spread of the AIDS virus is cultural as well as biological. The actual transfer of the virus from monkey to man may have involved something as boring as a monkey bite or a monkey hunter’s cut on the hand while butchering his prey. Some experts believe that AIDS might have died out with that hunter, or perhaps with his isolated village, had profound cultural changes not come to Africa. Over the last 30 years, the population of subSaharan Africa, the region hardest hit by AIDS, became increasingly urban. In1965, 5 percent of Tanzanians lived in cities; by 1987, it was 29 percent. Kinshasa, Zaire, swelled from a town of 400,000 in 1960 to a megalopolis of 4 million. At the same time AIDS exploded in the cities, largely through heterosexual contact. As in the United States, infection rates appear far higher in African cities than in rural areas. According to Gerald Myers, a molecular biologist at Los Alamos National Laboratory who studies the evolution of the AIDS virus, both strains of HIV are approximately 40 years old. That places the most recent transfer from monkey to man shortly before the period of widespread urban development.
    As with the history of most plagues, tracing the precise movements of the AIDS virus through various populations is exceedingly difficult. No one knows for certain whether the virus grew to epidemic proportions in rural areas or in the cities, where the soaring rates were first identified. Besides, says David Heymann, chief of the global AIDS program of the World Health Organization in Geneva, "The origin of AIDS is not the real problem; the real problem is where the disease is going." Scientists may breathe a sigh of relief when they can rule out the polio vaccine, but in the end we may never know the whole story of how AIDS began.
Sabin and Koprowski created their vaccines by culturing a strain of polio virus on monkey kidneys, supposedly the source of ______, now called SIV.
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答案the simian AIDS virus
解析 本句答案来自第四段的最后一行。
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