The causes of the more rapid emergence and spread of these "killer" viruses and pathogens are not entirely known, but are thought to be caused by some combination of deforestation with urbanization of wild virus habitats, evolutionary mutations and rapid global travel. Annually, an estimated 3.8 million Americans are transfused with 28.2 million blood components derived from 12.8 million units of blood donated by apparently healthy volunteers. A rigorous scrutiny of blood donors and the screening of donated blood for various serological markers have significantly reduced the mortality and morbidity due to transfusion-associated infectious agents. Some enzyme immunoassays used for routine screening may detect viral antigens or antibodies, but not the infectious agents themselves. Thus, there could be an asymptomatic window period of infectivity responsible for a residual risk of post-transfusion infection. Current approaches such as pasteurization, solvent-detergent (SD), UV irradiation, and chemical and photochemical inactivation are not always effective against a wide spectrum of pathogens, are sometimes encumbered by process-specific deficiencies, and often result in denaturation of the biologics that they are designed to protect.

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