Disease transmission by blood products: past, present and future.

Transfusion of blood and blood products has been associated with transmission of infectious agents. However, it is probable that blood products are currently very safe and that pooled virus-inactivated products from remunerated donors are now safer than untreated single voluntary donor components. Although the transmission events of the past and the present are reasonably well understood, reliance on a linear approach to predict safety in the future is open to criticism. Indeed, it was not possible to predict the extent or consequences of the AIDS epidemic or of hepatitis C transmission. Moreover, although variant Creutzfeldt-Jakob disease (vCJD) may not be transmitted to any large extent by transfusion of manufactured blood products, this will be due more to good fortune than good judgement - this agent could have escaped the screening, testing and eradication methods on which current confidence in blood product safety depends. Similarly, the emergence of a highly resistant non-enveloped virus, or even of another previously unrecognised disease-causing agent, could result in new threats from transfusion of blood components and products. The ecology of blood transfusion is exquisitely sensitive to variations in starting conditions, a situation typical of a chaotic rather than a linear system. Seemingly trivial events, often apparently unrelated to blood transfusion, have had enormous consequences in this field. Whatever the events that introduced simian immunodeficiency virus to humans or scrapie to cattle, they were a long way from those involved in the manufacture of blood products. In such a setting, reliance on methods that deal effectively with known threats (such as encapsulated viruses and bacteria) without adequate investigation and management of the intrinsic sensitivity to unpredictable events, leaves open the possibility of further infections emerging in the future. It is this reality that will ultimately result in the eradication of the transfusion of donor-derived blood and blood products in the developed world. In addition, all infections with a long disease-free incubation period in the host that can be transmitted in blood will eventually be over-expressed in groups that are exposed to blood either recreationally or professionally. As in the past, this could have occurred before testing or decontamination processes have been developed for emerging pathogens. Failure to be able to rely on completely risk-free donors, in both the voluntary and non-voluntary sides of the blood industry, continues to offer the potential for the transmission of infectious diseases in the future.