快猫短视频

AN EPIDEMIC of smallpox could sweep rapidly through the modern world if the
virus ever got out, a British study warns. Although smallpox is not as
infectious as diseases such as chickenpox or measles, there could be
鈥渟ignificant鈥� epidemics.

In the past, the spread of smallpox was held back by vaccination and people鈥檚
natural immunity. But since the disease was eradicated in 1979, vaccination has
ceased and levels of immunity have dropped dramatically. While all remaining
stocks of smallpox are supposed to be locked up safely in two labs in the US and
Russia, the anthrax attacks in the US have fuelled fears that terrorists might
get hold of the virus.

So Steve Leach at the Centre for Applied Microbiology and Research at Porton
Down near Salisbury decided to estimate the transmission rate of smallpox in
Western countries using historical records from Europe and North America. His
team found that before 1900, every infected person in an unvaccinated population
infected about five others, on average. In crowded conditions, such as
18th-century London or in hospitals, the figure rose to between 10 and 12. This
was the rate during the isolated European outbreaks of the early 1970s.

Today, the secondary infection rate would be between 4 and 6 in the community
and up to 12 including hospital-acquired infections, they estimate. Quarantine
and vaccination would halt the virus鈥檚 spread, but epidemics would still happen
if outbreaks were not detected quickly. Although most people recover from
smallpox, up to a third die.