Pathogen inactivation

A process designed to eliminate pathogens from water, air or donated blood. Pathogens include viruses, bacteria, and fungi. Sewage purification systems depend upon pathogen inactivation to purify water to the extent it may be safe enough to drink. Air purification systems may incorporate a HEPA filter to cleanse the air of germs. Pathogen inactivation in blood targets DNA or RNA of pathogens while ignoring components used in transfusions. The components in transfusions, red blood cells, platelets, and plasma, do not contain genetic material, therefore are unharmed.

One form of pathogen inactivation for blood uses a chemical that, when exposed to ultraviolet light, binds to the genetic material. The bonds prevent the two strands of DNA’s double helix from unzipping, thereby preventing germs from replicating. RNA, the genetic material in some viruses such as HIV, is similarly immobilized. There is current concern as to whether the technique can inactivate all viruses when they are present in large numbers. The technique is not designed to inactivate prions, which cause mad cow disease and its human equivalent, variant Creutzfeldt-Jakob disease, because prions are proteins and do not have DNA or RNA. And the process cannot be used to clean up white cell packs for transfusion because white cells have a nucleus and it contains DNA (so the process would inactivate the white cells).

A platelet system uses a synthetic chemical known as a psoralen and a chain of three transparent plastic bags connected by tubes. The platelets are put into the first bag where they come in contact with psoralen. They drip into the second bag, which is placed in a machine photocopier to expose them to ultraviolet light for about three minutes. Then in the third bag, an absorbent material removes the psoralen. Different chemicals have to be used for the pathogen inactivation of red blood cells because light cannot penetrate these cells to activate a psoralen.

The technique of pathogen inactivation is expected to add appreciably, perhaps $50 to $100, to the cost of a unit of blood. Red cells currently cost $100 to $200 a unit and platelets from $200 to $600. However, the technique improves the safety of transfusions. Platelets are stored at room temperature and are therefore prone to bacterial contamination which is believed to kill about 8 to 12 people and make many more ill every year in the US.

Red blood cells are refrigerated so that bacteria are less often a problem. Still, numerous other possible infective agents exist in blood. These include viruses such as hepatitis B and other forms of hepatitis and parasites such as those responsible for malaria and Chagas disease, which is widespread in Latin America and can fatally damage the heart after many years. These nonbacterial agents of disease can all be inactivated by the process of pathogen inactivation.

(Entry based in part on Technique may improve safety of donated blood by Andrew Pollack in The New York Times of April 2, 2002 and information from pathogen inactivation technology companies.)