Safer Blood Transfusions

Meera - Until 1991, blood transfusions were a common cause of hepatitis C infection, as the virus is spread by blood to blood contact. Famous figures such as the late Anita Roddick, founder of The Body Shop and stuntman, Evel Knievel were believed to have contracted hepatitis C in this way. But since 1991, the virus has been screened for in all blood donations in the UK. So just how do our blood services screen for not only this virus but other infectious agents as well? And as a result, how safe is our blood? Tofind out, I spoke to Jean-Pierre Allain, Professor of Transfusion Medicine at the University of Cambridge.

Jean-Pierre - Actually, we screen essentially for viruses and there are three main viruses we are screening for. The first one and most well-known is HIV, the second is hepatitis B virus or HBV, and the third one is hepatitis C virus or HCV.

Meera - How do you actually go about testing for these blood samples? So, somebody comes in to give a donation, what happens?

Jean-Pierre - First, we ask the potential donors to fill a questionnaire regarding potential infections and we also ask questions about their sexual behaviours because it has to do with the higher risk of infections, and also about drug abuse. Then we collect two tubes of blood, one with which we test for evidence of viral infection, essentially antibodies to HIV and HCV, and for hepatitis B surface antigen. In addition to that, with the second tube, we test for the genome of the virus. In other words, a direct gene or nucleic acid of the virus.

Meera - How do you actually go about looking for antibodies in somebody's blood and what does this tell you then about their infections?

Jean-Pierre - When we test for antibodies, we are looking to determine whether the individual has been in contact with the virus or not. We detect these antibodies by capturing the antibodies on a range of antigens from the virus itself. If the antibodies are present, they are binding to these antigens and then we detect the presence of antibodies.

米拉,那么发生在下一步you start looking at the genomes of these viruses?

Jean-Pierre - Every blood sample is tested for this genome. Actually, not individually like we do for antibodies, but in what we callpoolsof samples from the donors - at the moment, this pool is 24. When we test for the genome in these pools of 24 and we find a positive reaction, then we go back to the individual donations to identify which donor is responsible for the pool being positive. Then we correlate that with the antibody being found separately.

Meera - Now I imagine when looking for particular genomes of the virus, it must be quite difficult because viruses evolve very rapidly. So, which part of the genome do you look at?

Jean-Pierre - The virus itself has a tendency to easily modify its genome. So eventually, it could be difficult to detect. Except that we choose an area of the genome we know is what we callconservedwhich mean that it doesn't change at all or very little.

米拉-为什么这个面积守恒?

Jean-Pierre - Because it's functionally critical. And the more critical it's functionally for the virus to replicate, the more it needs to stay the same.

Meera - Now, having done all of these tests and looking into the blood, what is the risk of somebody now who receives a blood transfusion receiving infected blood?

Jean-Pierre - If we talk about the hepatitis C virus and HIV, the risk is calculated at about 1 in 3-5 million which means that it's less likely to be infected than being hit by lightning if you stroll on a Sunday afternoon.

Meera - Jean-Pierre Allain from the University of Cambridge. So we now know how we screen for viruses that we know of and know the biology of, but what about infections that we haven't met before? What about the unknowns? I asked Lorna Williamson, Medical and Research Director for NHS Blood and Transplants.

Lorna - Virtually every blood donation that's collected is separated into different parts. When people say blood transfusion, they generally mean the red blood cells which are given to carry oxygen and treat bleeding and severe anaemia. But we also can take the plasma, the liquid part of blood, and that is used to replace clotting factors in patients who are bleeding, and then finally, we can make blood platelets which are little discs that circulate in the blood and they are also important to prevent bleeding. We try as hard as possible to remove all the parts of blood that won't benefit the patient. We filter out the white blood cells which, in a transfusion, don't offer any benefit. If the patient needs red cells, we will take away all the plasma and we can give the patients exactly what they need and no other part of the blood. And then where we can, we would alter the blood donation in some way to try and kill or remove any viruses or infectious agents. So for example, plasma can be heat treated or treated with chemicals and there are new methods coming through to treat platelets with chemicals to kill viruses and bacteria.

Meera - How does treating them with heat help make them safer and remove any viruses?

Lorna - Well it simply prevents the virus genome from replicating. It destroys the ability of the DNA and RNA to copy itself, so the virus can't multiply.

Meera - As well as heat treatment. What other precautions that are taken?

Lorna - What we would really like would be a method of either heating or treating with chemicals the red blood transfusions which are the biggest type of blood product that's used and such methods are in development. The one thing we are assessing for blood transfusions are new filters to remove infectious agents called 'prions.' They're small bits of protein that cause prion diseases like variant CJD and BSE in cattle.

Meera - And what do you think, just lastly then, the kind of risks are of any infection or viruses that you just really aren't aware of at the moment and how prepared do you think the system is to deal with this?

Lorna - So we work very closely with the Health Protection Agency where the monitoring systems for infections that may come to this country from elsewhere in the world. Swine flu is a good example of that. There are also systems for monitoring infections in farm animals and we work very closely with other blood services throughout the world. With migration and international travel, infectious agents can move around the world very rapidly. So, it is a case of maintaining high vigilance on an international level.