RISKS IN PIG XENOTRANSPLANTS

 

Unfortunately, the act of transplanting an organ from an animal to a human still confers with it a high risk of transferring micro-organisms. This problem may be countered by breeding donor pigs under controlled, pathogen-free conditions. Yet, even seemingly healthy pigs may be carrying hard-to-detect zoonotic (capable of affecting humans) infections.

Alas, the procedure for assessing such risk is neither well defined nor established. On the one hand, the risk of human infection by pig viruses has never been an issue, despite hundreds of years of species interaction. Essentially, it can be stated that the probability of infection is uncertain at best. Yet, the possible dangers, as outlined below (Xenotransplants, 1999) are serious and deserving of scrutiny:

? "Many of the viruses of concern in xenotransplantation are not of major significance in veterinary medicine so that new asssy systems have to be developed.

? Xenotransplantation may overcome the natural barriers to infection, particularly the mucosal barrier, so that organisms can spread more easily in the human host, thereby obviating the need for a vector to transmit infection.

? Administration of immunosuppressant may enhance the activation of pathogens.

? Organisms carried by the xenograft may not be pathogens in the natural host but may become pathogenic in the human recipient.

? Novel, unknown animal-derived organisms could cause unknown clinical syndromes and would escape early detection.

? Strategies to alter the components of the immune response in the recipient or in the donor may alter the host's susceptibility to organisms."

 

RISKS IN BABOON XENOTRANSPLANTS

In the case of baboon transplants, the risk of transmitting infectious disease is well established. They have been long known to carry infectious agents that pose serious health risks in humans (including Mycobacterium tuberculosis, herpes viruses, exogenous retroviruses, and Marburg virus). To illustrate, one 1994 study of 31 adult male baboons in Pittsburgh determined that 52 percent were inadequate donors "in view of positive results with regard to retroviruses and toxoplasma (Xenotransplants, 1999).

Of particular concern is that baboons have been known to be infected with simian immunodeficiency virus (SIV), which is similar to the virus that causes AIDS in humans. The human immune system has already demonstrated a weak ability to eliminate other simian retroviruses of baboon origin (Allan et al., 1998); the same case may apply for SIV. Ironically, it is believed that the same evolutionary relatedness that makes humans compatible with primate organs leaves them vulnerable to primate disease as well.

 

 Source: Stanford University