Britain takes prion data on board
Latest worrying research on mad cow disease presented to UK committee.
The ongoing threat of prion disease was hashed over by a UK government advisory committee this week. They heard evidence from recent studies of these deformed proteins, which cause mad cow disease and its human version, new-variant Creutzfeldt-Jakob disease (vCJD).
The committee will use the information to help formulate advice for UK food agencies and blood banks on whether they should take further measures against prion infections. "We have become more rather than less anxious," says Marc Turner from the Scottish National Blood Transfusion Service, Edinburgh.
Scottish National Blood Transfusion Service, Edinburgh
British blood banks have already taken action to reduce prion content in blood products by, for example, removing white blood cells. They may also consider prion filtering, although this would be very expensive, and they could exclude donors of certain ages, although this would dramatically reduce blood supplies. "We are in a position of trading risks," says Turner.
One study presented to the committee suggested that Britain could be hit by a second wave of vCJD. Scientists say that there could be thousands of Britons infected with the deadly brain disease who do not show any symptoms. These carriers mean the infection could spread widely, through surgery or blood transfusions, even if tainted beef is removed from the food chain.
Since 1995, 148 people have died in Britain from vCJD. The deaths peaked in 2000, and now appear to be tailing off; nine people died in 2004.
Azra Ghani, an epidemiologist at Imperial College London, points out that there is a huge discrepancy between the number of people who have died and the number expected to die given the seeming prevalence of prions. Out of more than 12,000 tonsils and appendices from British patients, 3 contained prions1. Scaling up to the entire population, one would expect 7,000 people to have vCJD. (see ' Tissue survey raises spectre of 'second wave' of vCJD' ).
One explanation is that many people do have the disease, but only 10% show symptoms, says Ghani. If it can be shown that the carriers will sustain an epidemic in Britain, she says, "something drastic will have to be done".
Another study presented to the committee raised the prospect that current measure to remove tainted beef from the food chain may not be enough.
Scientists think that prions are generally confined to nervous and lymphoid tissue, such as the brain and tonsils. But a recent paper found that genetically engineered mice with a certain inflammatory condition accumulate prions in organs throughout their body2. If the same holds true for cows, then infected meat could enter the human food chain.
"It is a very interesting and thought provoking paper, but does not necessarily reflect reality," says Christopher Higgins, a director at the UK Medical Research Council and chairman of the committee. "I'm sure more work on this will be done."
- Heikenwalder M., et al. Science 307, 1107 - 1110 (2005).
- Clarke P. & Ghani A. C. J. et al. Roy. Soc. published online, doi: 10.1098/rsif.2004.0017 (2005).