Volume 1: Findings and Conclusions
1. Introduction
Transmission to humans

55 The two most worrying questions people ask about BSE are:

• Is it certain that the victims of the variant form of CJD have caught BSE?
• And, if so, how many victims are there likely to be?

56 We shall here summarise our conclusions about the link between BSE and vCJD, which are the subject of more detailed coverage in vol. 2: Science and in vol. 8: Variant CJD.

57 The unusual clinical features and novel pathology of the early cases of CJD in young people suggested this was a new variant of the disease. Much experimental work has been done to investigate whether there is a link between this new variant of CJD and BSE, and we believe there is now sufficient evidence to be confident that vCJD is caused by the transmission of BSE to humans. In outline, the main evidence, in addition to the temporal and geographical association of the two diseases, which leads us to reach this conclusion is as follows:

1. in strain-typing studies in both mice and primates the disease patterns (incubation period and disease pathology) of BSE, vCJD, feline spongiform encephalopathy (FSE) and TSEs of exotic ruminants were shown to be extremely similar, ¹ while differing from those of scrapie and sporadic CJD;
2. patterns known as glycosylation patterns, produced by analysing samples of brain using a technique called western blotting, are the same for BSE and vCJD. The patterns for BSE and vCJD are different from those for other TSEs such as sporadic CJD and iatrogenic CJD; and
3. in transgenic mice in which the mouse prion gene has been replaced by the bovine prion gene, inoculation with tissue derived from BSE-infected cattle produces the same disease pattern and incubation period as inoculation with tissue derived from patients with vCJD.

58 It is not possible to say whether BSE was transmitted to humans through consumption of beef or beef products, or by some other means; nor is it possible to say when individual infection occurred. There are a number of other unanswered questions:

• Why does vCJD affect young people? Possible explanations meriting further investigation include: the possible disproportionate consumption by young people of beefburgers, some of which contained high-risk material; higher incidence of infections such as tonsillitis or gastroenteritis in children than adults, giving rise to transmission through broken skin or mucous membranes; infection through gum lesions associated with eruption of teeth; and transmission via childhood vaccines prepared in cultures containing bovine constituents.
• How many more people will succumb to vCJD? To attempt to answer this question is not required by our Terms of Reference, nor would we feel able to do so. Estimates of the possible size of a vCJD epidemic are made difficult by the many variables associated with the disease. Many important factors in determining the likelihood of BSE transmission to an individual are unknown, such as dose, route of exposure, incubation period, genetic susceptibility and scale of the species barrier between cattle and humans. Nevertheless, several groups of epidemiologists and statisticians have attempted to predict the possible number of cases. Projections have in the past ranged from small numbers to many millions and it is not possible at this stage to reach a firm estimate.
• Is occupation a risk factor in vCJD? Among occupational groups exposed to BSE, to date farmers are the only group to have an excess over the incidence of CJD for the population as a whole. Between 1990 and 1996 four cases of CJD occurred in farmers who were known to have had cases of BSE on their farms. In addition, two farmers' wives succumbed to CJD. The affected farmers were aged between 54 and 64 and had signs and symptoms typical of sporadic CJD. They did not have glycosylation patterns associated with vCJD. To date, no one has demonstrated a link between these cases and BSE.