T By Jeffrey Kahn

he news that the West Nile virus might have been spread from a Georgia organ donor to four organ recipients is raising concern. The case also raises the possibility that the virus can be passed to others by blood and blood products, in addition to organ transplant.

What risk could West Nile and other blood-borne viruses pose to organ and blood supplies? How can they be addressed, and what does that mean for donors and patients?

Risk to the supply?

If viruses such as West Nile can be passed by organ and blood donation, then a new test will need to be developed to screen them before they’re used for patients. The same practice is used for the other diseases – such as HIV, some forms of hepatitis and a range of sexually transmitted diseases.

The West Nile case points out is that there are so-called emerging diseases that we can’t plan for in advance and sometimes don’t recognize or properly understand for many years. HIV is one such example from the recent past.

The reality is that we can never get to zero risk in organ transplant or blood transfusion, and so the risks need to be outweighed by the benefits they offer. The information needed to understand these risks and benefits needs to be part of the discussion with both recipients and donors – or their families – as part of their decision-making processes.

The West Nile case in question comes from an organ donor who had died, but an increasing number of donated organs, and all blood donated for transfusion, come from living donors.

Until a test is developed for screening organs and blood for new viruses, living donors will need to be asked about their history of mosquito bites in areas where the virus is known to be circulating. But with such broad screening techniques, many people who are not infected might be rejected from donating, depleting the already short supply of organs and the sometimes tenuous supply of blood.

We need to balance the value of reducing the risk of transmission through such crude screening techniques against the loss of often lifesaving donations, many of which will be untainted.

West Nile is the latest of infections that seem to be passed by blood and organs, and there are no doubt many others in our future. This unknown risk is also one of the major stumbling blocks in xenotransplantation – transplanting organs from animals to humans.

All this should make us realize that there are and always will be unknown risks. So we should set limits for acceptable risk in ways that balance them with the benefits that come with them.

Even with the current worries about the West Nile virus, we need to remember that the blood supply and donated organs are still overwhelmingly safe. When it comes to diseases such as West Nile and the risks they pose, the most effective approach is to avoid them altogether.