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From: TSS (216-119-162-20.ipset44.wt.net)
In Reply to: Swiss rise in CJD raises concerns over possible BSE link posted by TSS on November 29, 2002 at 8:08 am:
BSE may cause more CJD cases than thought The eating of BSE-infected meat might cause classical CJD in people, as well as variant CJD, a new mouse study suggests. Classical CJD, also called sporadic CJD (sCJD), is generally believed to develop spontaneously and existed before the BSE epidemic in British cattle, while variant CJD (vCJD) is thought to be the human form of mad cow disease. There has been a recent rise in cases of sCJD, in the UK in particular, but it was thought this was due to better surveillance and diagnosis. But the surprising new finding adds weight to suggestions that the rise is in fact linked to the BSE epidemic. The new work involved injecting the BSE infectious agent - a misfolded prion protein - into the brains of mice. The mice had been genetically modified to act as human models of infection and to be susceptible to CJD. As expected, some of these mice developed symptoms and a molecular subtype of prion protein misfolding associated with vCJD. But others developed a sub-type associated with the most common of three strains of sCJD previously identified in people. "This finding has important potential implications," the team led by John Collinge at the MRC Prion Unit in London, UK, writes in the EMBO Journal . "It raises the possibility that some humans infected with BSE prions may develop a clinical disease indistinguishable from classical CJD." Models predicting the future extent of the human epidemic associated with eating BSE-infected meat are based on the observation of vCJD in the population. But if BSE prions can also cause sCJD, these models will underestimate the ultimate human death toll. To date, 117 people have died in the UK from vCJD. Steady rise More sCJD deaths are recorded annually than vCJD deaths. In 2001, 53 people in Britain died from sCJD and 20 from vCJD. This compares to 35 from sCJD and three from vCJD in 1995, when the variant form was first identified. The steady rise in the recorded incidence of sCJD has been put down to better detection. "What we're speculating is that a proportion of that rise, not all of it but a proportion, is due to BSE," Collinge says. In Switzerland, which had the highest incidence of cattle BSE in continental Europe between 1990 and 2002, there has been a doubling in the number of sCJD cases in that period. But establishing how many, if any, cases of sCJD in people resulted from BSE infection will be very difficult, Collinge says. The two diseases cause similar symptoms, and the molecular type of sCJD seen in the BSE-injected mice is indistinguishable from the human type identified before the first cases of mad cow disease. This is not the first study to link eating meat from an animal infected with a prion disease to sCJD. In March 2001, a French team found that one strain of scrapie - a prion disease present in sheep for centuries - can cause the same brain damage in mice as sCJD. This suggested that some cases of sCJD in people might be down to eating scrapie-infected sheep. Journal reference: The European Molecular Biology Organization Journal (vol 21, p 6358) http://www.newscientist.com/news/news.jsp?id=ns99993122 More people may have human form of mad cow disease than previously thought, scientists fear Nov 29 2002 The Western Mail THE number of people with a human form of mad cow disease could be much higher than originally thought, according to a study published yesterday. Since 1990, there have been 117 confirmed UK deaths from variant CJD, which until now was assumed to be the only disease linked to eating BSE-infected beef. But scientists at the Medical Re-search Council's Prion Unit in London believe they have identified links between BSE and a second type of the human brain disease - sporadic CJD. The Government's latest figures show that from 1990 to November this year, 588 people died from sporadic CJD, including 28 deaths in 1990, 63 in 1998, and 53 last year. The scientists, led by Professor John Collinge, cast further doubt on the safety of sheep meat by suggesting that more animals - including humans - could carry and transmit the diseases than previously thought. The researchers wrote, "It remains of considerable concern whether BSE has transmitted to, and is being maintained in, European sheep flocks." They said that given the widespread infection of sheep breeds with scrapie, it was possible some had contracted BSE but that this infection had been hidden by the other disease. A full study is needed of all the tonsils surgically removed over a 12-month period - around 80,000 - to map the extent of CJD infection in the population, the Medical Re-search Council argued. The Department of Health is thought to be considering such a plan. The research team used a series of experiments on mice that had been genetically altered so they would display the human effects of a prion - an infectious protein. The "transgenic" mice were then exposed to BSE-infected material and the changes in the prion protein were monitored. As expected, some developed vCJD, but the researchers wrote that, "surprisingly", other mice showed effects of sporadic CJD. "These data suggest that more than one BSE-derived prion strain might infect humans; it is therefore possible that some patients with ... sporadic CJD may have a disease arising from BSE exposure," they wrote. The researchers said their findings were important when considered with the present sporadic CJD outbreak in Switzerland, which had the highest incidence of cattle BSE in Europe over the past 12 years. There was a two-fold increase in sporadic CJD in the last 18 months in Switzerland, while cases of vCJD remain low, a spokesman for the MRC said. http://icwales.icnetwork.co.uk/0100news/0200wales/page.cfm?objectid=12412033&method=full&siteid=50082 TSS
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