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- Transplanting animal organs into humans could trigger
a global pandemic of a deadly new disease. A new study by British scientists
has found that cancer-causing retroviruses are spread relatively easily
between different creatures in the wild.
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- The discovery, outlined last week by the Natural Environment
Research Council, will reinforce concerns raised by experiments which recently
revealed that pig hearts and kidneys carry potentially deadly animal retroviruses,
dashing hopes that animals could one day supply spare parts for human surgery.
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- As a result of these initial experiments, Western health
authorities imposed a moratorium on all xenotransplant surgery, although
biotechnology companies are known to be continuing with research. Human
organs are desperately scarce, as are supplies of brain tissue for treating
stroke victims and Parkinson's sufferers. It was hoped specially-reared
animals, mainly pigs, would provide tissue and organs for tens of thousands
of operations a year.
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- The dangers of this plan are underlined in the study
by biologists Michael Tristem and Joanne Martin of Imperial College, London,
which focused on murine leukaemia viruses, close relatives of the cancer
retroviruses that are known to infect pigs. Traces of virus DNA were found
in a range of mammalian species in the wild, suggesting that pig retroviruses
are capable of infecting other animals - including humans - with relative
ease.
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- 'There are two ways to demonstrate that animal retroviruses
pose risks,' said Tristem. 'You can show they can be grown in human cells
in the laboratory. Scientists have done that. Or you can show such viruses
jump easily between species in the wild. Our study now proves this also
happens - that cancer viruses will jump species in the real world, not
just in artificial laboratory settings.'
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- Finding leukaemia virus DNA mixed up with the genes of
different animals does not prove these creatures were all made ill by their
infection, Tristem admitted. 'However, when viruses jump species they usually
acquire pathogenic properties, just as HIV did when it leapt from monkeys
to humans. There is a real, but small risk that pig organ transplants could
trigger a new disease epidemic.'
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- Virologist Professor Robin Weiss, who first demonstrated
that pig viruses could infect human cells, agreed. 'Xenotransplants do
not seem to pose a big risk. But then BSE or HIV were not thought to pose
big risks when they were first discovered. We obviously have to be very
careful.'
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- Professor George Griffen, a member of the UK Xenotransplantation
Interim Regulatory Authority, said: 'There is always going to be a chance
that a viral stowaway could be transplanted into a human along with a pig
heart or kidney. It could then spread through his or her body, and then
to other individuals, triggering a new epidemic.
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- 'However, if the risk of this happening is found to be
very, very small, would it be right to block xenotransplants, given that
they could help treat so many serious illnesses? And don't forget that
none of the hundreds of pre-moratorium xenotransplant recipients have yet
to show reactions to retroviruses.'
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- Sceptics point out that transferred viruses could take
decades to take effect, and these transplant patients could still develop
retroviral illnesses in 20 years. They also argue that stem cell surgery,
in which the patients' own cells are used to grow new organs, could soon
obviate the need to use animal hearts or livers. 'I think it is now touch
and go whether xenotransplants will ever be given the go-ahead in the West,'
said Griffen.
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- Even if they were approved, operations would only be
permitted under the most stringent conditions. Patients would have to be
monitored and tested for the rest of their lives, as would their sexual
partners and children.
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- What worries some researchers is the prospect that these
costly lifetime safeguards may drive an unscrupulous surgeon or biotech
company to carry out transplants in 'xeno-havens', developing nations that
do not impose regulations.
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