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Scientists raise concerns about second wave of ’mad cow’ prion infection

04.11.2004


Leading experts address need to reduce risk to global blood supply

There is increasing evidence that infectious prions that can cause variant Creutzfeldt-Jakob Disease (vCJD), the human form of "mad cow" disease, can be transmitted through blood transfusion, according to Roger Eglin, Ph.D., Head of National Transfusion Microbiology Laboratories for the English National Blood Service. He spoke at a symposium on Transmissible Spongiform Encephalopathies (TSEs) where he was joined by prominent government, public health and blood safety experts from around the globe, including the U.S. and Canada, who raised concerns about a second wave of the disease brought about by human-to-human transmission via blood transfusions.

The panelists convened to discuss the adequacy of safeguards and precautionary measures to prevent human-to-human transmission of this fatal, neurodegenerative prion disease at a symposium held last night at the annual AABB blood banking conference in Baltimore, Maryland. The symposium was sponsored by Pall Corporation (NYSE: PLL), the global leader in filtration technology.

Citing two confirmed cases in the UK, where vCJD was transmitted via blood transfusions from donors who were young and apparently healthy at the time of donation, Dr. Eglin said the current decline in reported cases could be followed by a new wave of vCJD infections around the world of unknown magnitude. These concerns were echoed by the panelists, who noted the increase of vCJD in France from six to eight cases in just the past few months and the news that blood from a vCJD-infected donor was transfused to 10 people and used to manufacture medicines. "This may not be a disease in decline, despite the low number of cases today," said Dr. Eglin. "There is much uncertainty over the number of cases predicted for the UK. Estimates of up to 25,000 total cases have been predicted with an incidence of one in 24,000 of the UK population."

The second case of transfusion-transmitted vCJD in the UK demonstrated that two human genotypes are susceptible to the infectious prion, rather than one, as had been previously reported. According to Dr. Eglin, this extends the number of people at risk from 40 to 90 percent of the UK population. Since people can incubate vCJD with no clinical signs or symptoms of disease for a decade or more, there is no way to determine who or how many people may be harboring the fatal prion nor how many of these people may be blood donors. A single vCJD-infected blood donor has the potential to amplify transmission to several people, creating the basis for a far more widespread infection.

Dr. Eglin described the measures taken by the UK, including deferral of previously transfused donors and 100 percent leukocyte (white blood cell) reduction, to increase the safety of the blood supply.

Heightened vCJD Blood Concern in U.S.

David M. Asher, M.D., Chief and Supervisory Medical Officer with the FDA Division of Emerging and Transfusion-Transmitted Diseases at the Center of Biologics Evaluation and Research (CBER), expressed heightened concern about vCJD transmission by blood due to the two cases in the UK. He concurred that a second wave is possible and said that the number of people who may be harboring the infection in the UK, 237 per million, is a minimum estimate and may be too low.

The U.S. has a number of measures in place to protect blood safety, he said, but stated that it is not possible to remove every blood risk by donor deferral. "If we attempt to defer every donor who spent time in the UK from 1980 to 1996, the blood donor loss would be enormous," he explained. On October 14, the FDA TSE Advisory Committee made the recommendation that no additional residency deferrals are necessary in the U.S. at this time. "If exposure to an infectious agent can be stopped, then the disease can be stopped," said Dr. Asher. "Physical removal of vCJD from blood appears to be the most promising line of attack."

Dr. Asher also commented that species barrier protection from TSEs other than BSE is not absolute. He listed several TSE infections found in animals in the U.S., including Chronic Wasting Disease (CWD), which is found in both farmed and wild deer and elk in many Midwestern and Western states and parts of Canada. Although there is no evidence of transmission to humans, hunters are being warned to avoid contact with or eating the meat of animals that may be infected with CWD.

Precautionary Principle in Canada

Although Canada has detected only one case of BSE and one of vCJD to date, the country has taken a number of precautionary measures to help prevent further infections, similar to those taken in the UK, according to Dr. Peter R. Ganz, Director of the Centre for Biologics Evaluation (CBE), Health Canada. Dr. Ganz cited the Precautionary Principle – "If risk is possible, then we must err on the side of caution" – which, he said, drove Canada’s actions even before the emergence of possible vCJD transmission through blood.

Dr. Ganz noted that Canada’s surveillance system, its three deferral directives to exclude donors with the potential for infectious disease and the implementation of universal leukocyte reduction has reduced the potential risk of vCJD transfusion transmission by about 92 percent. He also spoke about the problems of balancing more stringent donor exclusion policies against the loss of available supplies of blood.

Laurie Garrett, Gates Senior Fellow in Global Health for the Council on Foreign Relations and award-winning author and journalist, stressed the need to take measures to prevent the spread of newly emerging infectious threats before they reach epidemic proportions. "Whatever microbes exist in developing and third world nations will eventually exist in our blood system because humankind is on the move as never before," she stated. "Because of the speed of global travel, the risks of developing countries are our risks. You may not feel global, but your microbes are."

She explained that we cannot rely on the developing world or even countries such as China, as evidenced by SARS, to stop infections before they are on everyone’s doorstep. "Fortunately, SARS is not transfusion-transmitted, but our own history of dealing with AIDS, our lack of proactive policies and the economics of action beg the question of whether we are ready to stop the spread of the next major blood-borne infection," Ms. Garrett added. "The most cost-effective approach is to be proactive and keep microbes out of the blood in the first place," she concluded.

Sam Coker, Ph.D., principal scientist and technical director at Pall Medical, presented the results of two new research studies with its Leukotrap® Affinity Prion Reduction Filter, which is in late stage testing. The filter has been shown to reduce infectious vCJD prions from red blood cell concentrates below the limit of detection of the Western blot assay. It was also found that the filter can remove different strains of infectious prions from blood, including scrapie. The new filter, which reduces both leukocytes and prions in a single step, is expected to be introduced commercially in Europe early next year followed by submission to the U.S. FDA.

Paul M. Ness, M.D., Director of Transfusion Medicine at The Johns Hopkins Hospital in Baltimore, editor-in-chief of Transfusion and former president of AABB, who moderated the symposium, reviewed issues in the U.S., commenting that inadequate reimbursement often prevents or delays the adoption of new technology to enhance blood safety. He said that improvements in transfusion safety are not likely to be implemented in the U.S. without patient advocacy.

Dr. Ness reviewed U.S. blood safety measures and noted that leukocyte reduction removes prions from blood, resulting in a 45 percent reduction of risk of vCJD transmission. He pointed out that although leukocyte reduction is valuable, and explained the importance of 100 percent implementation to improve patient safety, it is still not sufficient. "Filtration technology that removes both prions and leukocytes would be an example of adding value without adding another process that would significantly increase costs," he concluded.

Laura Constable | EurekAlert!
Further information:
http://www.pall.com

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