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Animal Organ Transplants
To Humans Could Trigger Deadly Global Disease Pandemic
By Robin McKie - Science Editor
http://www.observer.co.uk/uk_news/story/0,6903,346396,00.html
7-23-00
 
 
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.
 
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.
 
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.
 
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.
 
'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.'
 
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.'
 
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.'
 
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.
 
'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.'
 
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.
 
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.
 
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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