British scientists predict fewer deaths from mad-cow disease - ------------------------------------------------------------ PARIS: British scientists have cut by more than two-thirds the projected number of deaths from a brain disorder linked to eating tainted beef. Computer estimates by Oxford University's Wellcome Trust Centre put the maximum number of cases in Britain from variant Creutzfeldt-Jakob disease (vCJD) at 136 000 over the next 40 years. [This analysis published in the 10 Aug issue of the journal Nature by Ghani et al. (Nature 406, 583-584, 2000) concludes that current mortality data are consistent with between 63 and 136 000 cases among the 40% of the UK population with a susceptible genotype.] These figures compare with the Centre's estimate at the end of last year that up to half a million people could die. Estimates by other researchers have suggested a theoretical toll in the millions. The Wellcome Trust team said the big fall was because they believed it may be much harder for humans to catch the vCJD agent from animals than previously thought. The current data suggest that, on average, no more than 2 cases of vCJD could arise from the consumption of one maximally infectious bovine [in contrast to the previous estimate] of more than 100 cases per infected cow. "This suggests a substantial species barrier (to the infectious agent), given that thousands of people might eat material from a single animal." It added that the maximum toll of 136 000 would only occur if the vCJD agent proved to have a long incubation period of more than 60 years -- in other words, that vast numbers of people ate infected beef decades ago but were yet to exhibit any symptoms. If, on the other hand, vCJD had an incubation period of less than 20 years, the outbreak would soon peak. In that case, the total number of cases over the next four decades would be comparatively [small], between 75 and 630. Researcher Azra Ghani stressed that vCJD remained a new and still mysterious disease, which explained the enormous variations in estimates. "We just don't know which of these many scenarios we are going to end up with," she told Agence France-Presse. "It could either be that there is a strong species barrier and not many people will be infected, or it could be a (steady) trickle, an epidemic that is heading upwards and could be much larger." These scenarios, with their outcomes dependent on the incubation period, are based on there being a tally of at least 15 more cases of vCJD reported this year. Britain's Department of Health on Tuesday said the total number of cases, from 1 Jan to 4 Aug, was 13, bringing the total to 79. In addition, the Wellcome Trust model is also based on the assumption that the only people at risk will be those carrying a genetic sequence known to make them vulnerable to vCJD, which is about 40 percent of the British public. That [assumption] is contested by some scientists, who say it may be possible for people without this genetic sequence to catch the infectious agent and harbor it for years before they display any symptoms. - -- ProMED-mail <[EMAIL PROTECTED]> [The same issue of Nature carries an analysis of the incidence of scrapie in sheep during the BSE years (Gravenor et al., Nature 406,584-585, 2000). The experimental transmission of bovine spongiform encephalopathy (BSE) to sheep raised the possibility that some sheep in the UK could have been infected during the 1980's by exposure to BSE-contaminated feed. The symptoms of BSE in sheep are indistinguishable from those of the transmissible spongiform encephalopathy known as scrapie which has been endemic in Britain for at least 200 years. Analysis of the incidence of scrapie in sheep before, during and after the BSE outbreak, revealed no peak making it unlikely that there was any substantial epidemic of BSE in sheep. Consequently, it is unlikely that consumption of sheep meat during the BSE period has contributed to nvCJD in humans as some have feared. - Mod.CP] ..........................mc/cp/ds <A HREF="http://www.ctrl.org/">www.ctrl.org</A> DECLARATION & DISCLAIMER ========== CTRL is a discussion & informational exchange list. Proselytizing propagandic screeds are unwelcomed. Substance—not soap-boxing—please! 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