There has been uncertainty regarding the amount of BSE material that constitutes an oral infectious dose for humans. The study estimates that a person would have to eat at least 1.5kg of neural tissue from an infected animal that was just below the detection limit when tested negative at the slaughterhouse, to be at risk of developing variant Creutzfeldt-Jakob disease (vCJD).
Jean-Phillipe Deslys (Commissariat l'Energie Atomique, France) and colleagues gave two adult primates a 5g oral dose of ground brain tissue from a BSE-affected cow. One primate developed a neurological disease closely resembling vCJD 5 years after exposure, whereas the other remained free of disease. On the basis of these findings and data from other studies the investigators estimated that the efficiency of infection from cow to primate could be 7 to 20 times lower than that of intraspecies infection for cattle.
The results of the present study also suggest that the incubation period for BSE transmission from cattle to human can be more than a third longer than that of human to human transmission.
Dr Deslys states: "The present data do not provide a definitive minimum infective dose for transmission of cattle BSE to primates, but they do give enough information for a preliminary assessment of the adequacy of existing measures to protect the human food chain.
"Our results provide reassurance that BSE screening procedures combined with CNS removal are effective measures to protect the human food chain."
In an accompanying commentary James Ironside and Mark Head (National Creutzfeldt-Jakob Disease Surveillance Unit, University of Edinburgh, UK) write that the precise implications of this study for vCJD are difficult to assess since the number of animals used in the study were small and the minimum infect
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