快猫短视频

HEALTHY animals can carry an infectious form of the prion disease scrapie
without ever developing symptoms, say researchers in London. They have found
that symptom-free mice can harbour hamster scrapie for years, with enough of the
agent in their brains to infect other animals.

The results raise the possibility that many seemingly healthy cattle in
Britain鈥攁nd across Europe鈥攃ould harbour BSE, the prion disease that
can cause the deadly variant CJD in people. They also provide an unexpected
insight into the nature of prion disease.

快猫短视频s had assumed that animals inoculated with prions either succumbed
to the disease鈥攕ometimes after a long incubation period鈥攐r were
resistant to it. But the discovery that mice can live in perfect health with
large amounts of prions in their brains suggests a third possibility: that
prions alone are not what cause disease.

Many transmissible spongiform encephalopathies (TSEs) are already known to
cross species barriers. BSE, for example, can infect sheep, mice and even
marmosets. But symptoms take much longer to appear after cross-species
transmission. In a few cases, the species barrier seems insurmountable.

To investigate this further, John Collinge and his colleagues in the Medical
Research Council鈥檚 Prion Unit at St Mary鈥檚 Hospital in London injected hamster
scrapie into the brains of 18 young mice. Previous research suggested mice
cannot be infected by hamster prions. As expected, none of the mice developed
scrapie symptoms, and most died of natural causes after two to three years. Yet
despite their good health, all 10 mice that lived more than 659 days after the
injection had large amounts of the rogue prion PrPsc in their brains, Collinge
found.

To see if these mouse brains were infectious, the researchers then inoculated
healthy mice with brain tissue from one of these long-lived animals. All the
mice injected with the prion-filled brain developed scrapie in four months. The
results raised interesting questions about how prions cause disease, Collinge
told 快猫短视频. 鈥淲hy weren鈥檛 the 660-day-old mice showing symptoms
if they had as much prion in their brains as 100-day-old mice that die of prion
disease?鈥� He believes there might be unknown chemical factors that influence or
are influenced by the speed at which rogue prions build up. These could govern
how much damage is done to brain tissue. 鈥淭here could be an intermediate factor
having a toxic effect,鈥� Collinge suggests.

The new findings also suggest that extra checks may be needed to ensure that
BSE is not lurking unseen in sheep, pigs and chickens. Peter Smith, acting
chairman of SEAC, the British government鈥檚 advisory committee on prion diseases,
says that the committee has always acted on the assumption that there were
likely to be undetected cases of BSE. But he also pledged to investigate the
implications of Collinge鈥檚 findings at SEAC鈥檚 next meeting on 29 September.