Can CJD be transmitted through the blood supply?
CMAJ 1998;158:716-17
© 1998 Canadian Medical Association
Response from: B. Larke, J. Hoey
In response to: A. Giulivi
Although I am unaware of any direct evidence that new variant CJD "can be spread through the blood supply," there is nevertheless increasing concern over our complete lack of knowledge on this point. It is now generally accepted among investigators in this field that the strain of transmissible spongiform encephalopathy (TSE) responsible for the bovine spongiform encephalopathy (BSE) epidemic in the UK and the strain causing vCJD are identical and distinct from all other TSE strains characterized to date. Moreover, several factors have aroused concern that vCJD may lie outside the spectrum of even our limited knowledge of classic CJD and scrapie: the apparent ease with which BSE is transmitted orally, the readiness with which it has jumped species barriers (first to cattle from whatever species it originated in and then to domestic and wild cats, antelopes and finally humans), its unique clinical and histopathological presentation in humans, and recent reports that the protease-resistant protein amyloid (PrPres) is recoverable from the highly hematogenous tonsillar tissue of patients with vCJD but not those with classic CJD. Is the tonsillar PrPres transported there from the blood stream? Is there some essential hematogenous involvement in the pathogenesis that facilitates oral transmission and results in significant blood titres? (It is noteworthy that cross-species inoculations of blood preparations from cattle affected with BSE to mice have not resulted in infections, but these tests have limited sensitivity.) Is this strain more virulent than classic CJD strains? These questions cannot be answered at present, and attempts to answer them are still mostly in the planning stages. However, if there is a risk to the blood supply from this agent, the problem will not be confined to the UK. The North American donor population undoubtedly includes many people who have travelled to or resided in the UK or Europe during the BSE epidemic.
It is imperative that we learn more about vCJD and the role of blood in its pathogenesis and transmission. Because of the low infectivity titres associated with blood, such studies will inevitably be burdened by long incubation times, incomplete transmission and a requirement for large numbers of animals to achieve statistical significance. Working at the limits of sensitivity demands the highest standards of animal husbandry. The unknown risks to humans and the established risks to cattle posed by this agent require expensive containment to ensure safety. A credible assessment of the risk to the blood supply from this disease will necessitate a substantial commitment of resources and several years of data collection once the resources are in place. The sooner we begin, the better.
Robert G. Rohwer, PhD
Director
Molecular Neurovirology Unit
Veterans Affairs Medical Center
Baltimore, MD
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