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PCRM Asks FDA: Ban Cross-Species Transplants

Animal organs have been suggested as a possible, albeit remote, solution to the shortage of transplantable human organs. However, in over three decades of experimental transplants, no human recipient of an animal organ has survived.

In comments submitted to the Food and Drug Administration (FDA), PCRM is urging a ban on all animal-to-human transplants (xenotransplants). The FDA’s draft guidelines, currently under consideration, are too weak to safeguard public health.

The shortage of human organs is a solvable problem. While most Americans support organ donation, fewer than one in five has actually completed an organ donor card. By increasing overall organ donation rates by just 17 percent, deaths from lack of donor organs can be eliminated. In Washington, D.C. area hospitals alone in 1994, more than 200 patients who died were suitable donors, but their organs went unharvested.1 Improved tracking and harvesting of suitable organs can significantly diminish this shortfall.

Even more effective is to implement a policy of presumed consent. Under this system, unless individuals specify otherwise, all suitable organs will be used upon a person’s death. When Belgium enacted such a law, organ availability jumped 140 percent.2

Another method is to allow people to choose to make an organ donation provision when they renew their driver’s licenses or file income tax forms.

We can also reduce the need for donor organs through prevention programs. At best, even human-to-human transplants remain stop-gap measures, as most fail within five years, and, depending on the organ, between 9 and 40 percent fail within a year of transplantation.3

Heart, lung, and liver disease are, in many cases, preventable through proper diet, exercise, and avoiding the organ-damaging effects of smoking, certain medications, and heavy use of alcohol. Undoubtedly, genetics and other uncontrollable factors do contribute to organ disease, but rates can be greatly reduced through preventive efforts.

Even supporters of xenotransplantation concede that the risk of viral transmission is real. Transmitting animal viruses into immunosuppressed patients could open a Pandora’s box of disease. Influenza, Marburg, and Ebola viruses are known to infect humans and can cause catastrophic disease. One documented outbreak of Ebola in Zaire involved more than 200 people and had an 88 percent fatality rate.4 Most newly emerging human infectious diseases have been shown to come from other species.5-8

Many microorganisms do not cause disease in their natural hosts, but have serious pathogenic potential when transmitted to another species. For example, simian immunodeficiency virus (SIV) is found in nonhuman primates and is non-pathogenic in many species.4 However, SIV is transmissible to humans, and it is widely believed that Human Immunodeficiency Virus (HIV) is the result of a cross-species infection of a simian retrovirus.9

In organ transplants, natural barriers such as skin, mucosal surfaces, and the environment of the stomach are bypassed.5 Transplant patients who are intentionally immunosuppressed to prevent rejection of grafted material are more likely to contract diseases from host pathogens.

While some have hoped to reduce this risk by breeding “germ-free” animals for xenotransplantation, it is impossible to screen for all pathogens, and simply not possible to breed a completely germ-free animal.

Some experimenters have claimed that pig organs are less likely to harbor disease-causing viruses. However, a retrovirus that can infect human cells was recently discovered in pigs in the U.K.10 The virus is apparently present in all domestic pigs, and one strain quickly invades human cells, permanently inhabiting the new host’s system. As a result, British health officials are expected to withhold approval of planned pig-to-human heart transplants.

Xenotransplants are risky and expensive. They are not treatments, but experiments that have been universal failures. They do not serve the public health; rather, they put the population at risk of unknown and potentially lethal viral outbreaks.

References
1. Washington Regional Transplant Consortium. 1995.
2. Roels L, Vanrenterghem Y, Waer M, Gruwez J, Michielsen P. Effect of a presumed consent law on organ retrieval in Belgium. Transplant Proc 1990;22:2078-2079.
3. United Network for Organ Sharing. U.S. Transplants by Organ Donor and Type. 1996.
4. Institute of Medicine. Xenotransplantation: Science, Ethics, and Public Policy. Washington, DC. National Academy Press, 1996.
5. Allen JS. Xenotransplantation at a Crossroads: Prevention Versus Progress. Nature Med 1996;2:1.
6. Hjelle B, et al. A Novel Hantavirus Associated with an Outbreak of Fatal Respiratory Disease in the Southwestern United States: Evolutionary Relationships to Known Hantaviruses. J Virol 1994;68:2:592-596.
7. Morse SS, Schluederberg A. Emerging Viruses: The Evolution of Viruses and Viral Diseases. J Infect Dis 1990;162:1-7.
8. Murphy FA. New, Emerging, and Reemerging Infectious Diseases. Adv Virus Res 1994;4:1-52.
9. Desrosiers RC. A Finger on the Missing Link. Nature 1990;345:326.
10. Garrett L. Pig Virus Called Human Threat. New York Newsday. November 14, 1996. A37



 

Spring 1997

 Spring 1997
Volume VI
Number 2

Good Medicine
ARCHIVE

 
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