We are glad that FDA has issued guidelines that appear to amount to a ban on transplanting organs from other primates into humans (The Federal Register, April 6, 1999), but we find it disturbing that these guidelines appear to be limited to primate organs whereas the big push for xenotransplantation is coming from companies advocating the use of organs from genetically-altered pigs.

We are gravely concerned about the possibility of transplanting disease organisms along with the organs.  This danger is by no means limited to organs from primates, however.  All species carry a variety of microorganisms with which they have evolved a symbiotic relationship that is harmless, possibly even beneficial, to the host species.  Nobody knows what will happen when some of these microorganisms are released into a new species.  They may die or go on living as in their previous relationship with the original host, or, and herein lies the danger that concerns us, they may undergo a population explosion in a new host that has had no opportunity to develop defense mechanisms to contain them.  Worse yet, one or more of these organisms may create a new human disease that is transmissible to others, possibly even wildly contagious. 

We have only to look at the 1918 influenza epidemic that jumped from pigs to humans and killed over 20 million people worldwide to appreciate this worst case possibility.

In recent years, we have discovered or identified extremely virulent bacteria, viruses, and prions that can establish themselves in humans with severely debilitating, even deadly, results.  This is true of a number of very dangerous diseases like bovine spongiform encephalopathy ("mad cow" disease) which became new variant Creuzfeldt Jakob disease in humans.  We have also seen  Ebola and Herpes B make the leap from non-human to human primates, as well as a moribilli virus from horses infected by bats in Australia, a hanta virus from rodents,  eastern equine encephalomyelitis from horses, hemolytic uremic syndrome from beef,  and, of course, anthrax from sheep and cows, and, more recently, the chicken virus that infected humans in Hong Kong.Disease transmission from pigs to humans

Pig to human disease transmission is fairly common aside from the deadly flu epidemic of 1918 and the swine flu outbreak caused by vaccinations in 1976 that killed 113 people and paralyzed an estimated 3600..  Porcine Endogenous Retroviruses (PERV) have been found to infect human kidney cells in vitro, justifying the British Ministry of Health's decision to postpone the proposed transplantation of pig organs into humans.  Retroviruses are of particular concern because they can't be eliminated from the body, making an infected person a carrier for life. Pigs harbor aspergillis fungus which has been a source of central nervous system infection in kidney transplant patients.  Piggery workers in Australia were found to be infected with a previously unidentified pig virus that was causing stillbirths and birth defects in pigs.  Pigs also carry cytomegalovirus and other herpes viruses, polyomaviruses and parvoviruses that are known to infect humans.  Wahba babi is a newly identified pathogen that appeared in Indonesian pigs and people within the last few years.  The latest transpecies disaster occurred in Malaysia in the form of the Nipah virus that killed 100 of the 250 persons known to be infected and resulted in the slaughter of  about one million pigs to wipe out the disease, which has since reappeared.

The danger of transmission of known or as yet unidentified pig viruses via transplanted tissue and organs is acute because they are inserted into the body and hooked up directly to the circulatory, alimentary or pulmonary systems, bypassing the normal barriers of skin, stomach acids and mucosal membranes.  Transplanting organs from another species into humans  is akin to breaching a dam and inundating the immune system with a torrent of toxins for the body to handle all at once. Once inside a new host, even a host that is not immune-compromised,  pathogens have the opportunity to multiply with no opposing organisms in place to impose limits on their expansion.  Israel's Dr Andre Menache has compared this situation to a group of naughty children going berserk after being admitted to a new playground without supervision.

An experiment in Sweden reported by the Committee on Science and Medicine of the Council of Europe Parliamentary Assembly involved transplanting pancreatic islet cells from fetal pigs into human diabetics.  Ten of these patients were subsequently found to be harboring antibodies to swine influenza and five were found to have antibodies to porcine parvovirus. 

Other pig cell transplants have been performed without antibodies to pig diseases being identified, but British virologist Robin Weiss asked, "If there are negative results, does it mean that no one's been infected or that you can't detect it?"

Disease transmission is particularly worrisome in the case of diseases like Creuzfeldt Jakob's disease that have a long latency period before symptoms start to appear and in the case of retroviruses, which cannot be eliminated once they are established...Interspecies differences interdict cross-species transplants

Pig organs have evolved to support an animal with a lifespan of 10 years as opposed to 80 or more years for humans.  In addition, their organs are designed to function differently from the corresponding organs in humans:

• Pigs are a horizontal animal.  Their hearts have not evolved to pump blood against gravity into the brain of an upright animal.  This, besides the fact that they have evolved to support an animal with a shorter life span is sufficient reason not to attempt pig-to-human transplants in addition to the fact that all those that have been attempted have predictably failed as have transplants from other primates.
  

To compound the problems presented by interspecies differences, transplant patients' immune systems are deliberately suppressed with drugs in order to prevent rejection of the transplants , which a healthy immune system would see as a foreign invader and promptly reject.  Having a weakened immune system makes transplant recipients more susceptible to the opportunistic expansion of any stray organisms that might hitch a ride with a transplant.

Compounding the problem still further is the fact that the pigs used will have been genetically altered opening up still more possibilities for acquiring and transmitting.existing and as yet unknown diseases.  Xenotransplant proponents claim that their pigs will be carefully screened for viruses, bacteria, fungi and parasites, but, as Australian virologist Peter Kirkland  wrote in New Scientist, "You can't screen for viruses you don't know about."                                                                concluded on page 116