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| 2007-12-4 16:01:16 [点击数：2861] |
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Unit thirty-five
Xenotransplantation
Transplant surgeons work miracles. They take organs from one body and integrate them into another, granting the lucky recipient a longer, butter life. Sadly, every year thousands of other people are less fortunate, dying while they wait for suitable organs to be found. The terrible constraint on organ transplantation is that every life extended depends in the death of someone young enough and healthy enough to have organs worth transplanting. Such donors are few. The waiting lists are long, and getting longer.
Freedom from this constraint is the dream of every transplant surgeon. So far attempts to make artificial organs have been disappointing: nature is hard to mimic. Hence the renewed interest in trying to use organs from animals.
Doctors in India have just announced that they have successfully transplanted a heart from a pig into a person. Pressure to increase the number of such “xenotransplants” seems to be growing. In Europe and America, herds of pigs are being specially bred and genetically engineered for organ donation. During 1996 at least two big reports on the subject – one in Europe and on in America – were published. They agreed that xenotransplants were permissible on ethical grounds, and cautiously recommended that they be allowed. America’s Food and Drug Administration has already published draft guidelines for xenotransplantation.
The ethics of xenotransplantation are relatively unworrying. People already kill pigs both for food and for sport; killing them to save a human life seems, if anything, easier to justify. However, the science of xenotransplantation much less straightforward.
Import an organ from one animal to another and you may bring with it any number of infectious diseases. That much is well known. However, coping with this danger is not merely a matter of screening for obvious ills such as parasites. Many diseases that could harm humans may be both undetectable and harmless in their natural hosts. Diseases that have been dormant for years may suddenly become active if they find themselves in a new environment, such as a human recipients’s body. After that , they may start to infect other people.
The risk of this happening should not be underestimated. The DNA of every organism carries within it hundreds of ghosts of infections past. Such “retroviruses” – which include HIV, the virus that causes AIDS – always incorporate themselves into the DNA of their hosts. Many retroviruses (although not HIV) also incorporate themselves into their hosts’ eggs or sperm, and are passed passively from parent to child. Although it is true that most retroviruses gradually lose their infectious powers, some retain their ability to leap out of the host DNA – often much later. Certain pig retroviruses are probably among these.
Of course it is possible that none of the retroviruses will be harmful to humans: possible too that scientists will eventually isolate all prospective trouble-makers. But at a time when thousands of British cattle are being slaughtered because of the suspicion that they have a disease that may be transmissible to humans, it seems a reckless gamble to take.
transplant vt.1.移植,移种 2.移植(器官) n.(器官)移植
transplantation n.1.移栽,移种 2.移植(术)
surgeon n.外科医生
[联想词] dentist n.牙科医生
bruise n.青肿,挫伤 vt.1.打青,使受瘀伤 2.挫伤,伤害
scar 伤痕,伤疤
organ n.器官
[联想词] belly n.肚子
flank n.1.肋,肋腹 2.侧翼,翼侧
thigh n.股,大腿
bowel n.肠
gland n.腺
kidney n.肾(脏)
vein n.静脉,血管
recipient n.接受者,接收者
constrain vt. 1.限制,约束 2.克制,抑制
constraint n.1.限制,约束 2.限制(或约束)性的事物
donate v.捐赠,赠送
donor n.捐赠者,赠送人
mimic v.(mimicked; mimicking) 模仿 n.1.善于模仿的人 2.仿制品
[联想词] imitate vt.1.模仿,仿效 2.仿制,仿造
imitation n.1.模仿 2.仿制,仿制品,赝品
simulate vt.1.模仿,模拟 2.假装,冒充
hence ad.1.因此,所以 2.今后,从此
[联想词] henceforth ad.从今
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