Update on vCJD Transmission

James W. Ironside, United Kingdom

The understanding that variant Creutzfeld Jacob Disease (vCJD) has a long incubation period and the confirmation that it can be transmitted through blood transfusion has prompted the United Kingdom to undertake a study to determine the prevalence of the infection in the population. In total, 170 cases of active vCJD have been identified, at least three of which followed blood transfusion.

vCJD originated in cattle infected with bovine spongiform encephalopathy (BSE), which was transmitted from infected meat to the human population. The difficulty, according to Dr. Dr. James Ironside, Professor of Clinical Neuropathy at the University of Edinburgh, is the large numbers of asymptomatic carriers of the disease. The estimated prevalence in the population is 1 in 10,000, although that figure is not totally reliable, he warns.

Half of the infectivity present in blood appears to be in plasma. A risk assessment of prion transmission determined that the highest risk is through infected plasma products, particularly since there is still no screening test available for vCJD. Even a single vial of infected FVIII, FIX, or antithrombin poses a very high risk of prion transmission, he says, which means that many British patients with bleeding disorders have been exposed. As a result, a tissue study has been undertaken to search for evidence of vCJD infection, based on analysis of lymphoid tissues removed during surgery or autopsy.

To date, 17 samples have been examined and all but one were negative. The positive patient had no clinical evidence of vCJD but had severe hemophilia A; he died in his 70s of an unrelated illness. He had received 8,000 units of vCJD-implicated FVIII 12 years before his death and had had many blood transfusions during a number of surgical procedures. Although it is possible the patient may have been infected through dietary transmission, it does appear likely that the infection was through either the known infected FVIII or subsequent blood transfusions.

“There continues to be considerable uncertainty about how much infectivity there was in U.K. plasma,” Dr. Ironside says. “We don’t have a handle on how much dilution affects infectivity of the final product. There are 3,000 potentially implicated U.K. patients with bleeding disorders from batches going back as far as 1980, and none of them have developed active vCJD. If there was a significant infectivity rate, we would have expected to see a case by now,” he says.

Dr. Ironside’s state of the art paper, published in a special supplement of the WFH’s official journal Haemophilia, is available here.

Last Updated September 2010