杏吧原创

CLIMATE change could spread a lethal plague that would wreak havoc among
Britain鈥檚 rabbit population. The disease is already common in southern
Europe.

Rabbit haemorrhagic disease (RHD) was first recognised in China in 1984,
after arriving in imported German angoras. It then wiped out 140 million
domestic rabbits in China. The virus probably originated in Central Europe and
spread across the continent.

Italy lost 64 million farmed rabbits to the virus in 1986, while Spain now
imports wild rabbits to provide targets for hunters. In 1995, the virus was let
loose鈥攑robably deliberately鈥攊n Australia and New Zealand, where
rabbits are a major pest.

The disease reached Britain in 1994, but has had little impact. Peter White
of Stirling University in Scotland thinks this is because a harmless variant of
the virus, possibly the ancestor of the lethal strain, acts as a natural
vaccine.

In Britain, populations that are slowest to reproduce have the most rabbits
with antibodies to the virus, and are less likely to get the disease.
鈥淧opulations where fewer young rabbits survive every year have a higher average
age,鈥� says White. 鈥淥lder rabbits are more likely to have acquired the
non-pathogenic strain.鈥�

But even a small decrease in the proportion of immune rabbits can have
dramatic effects on susceptibility. And once the virus gets a foothold it can
wipe out whole populations. White suspects that RHD does so much damage in the
warmer climate of southern Europe because rabbits breed fast there. So the
percentage of older immune animals falls below the threshold needed to halt the
pathogen鈥檚 spread.

RHD already hits southern England harder than Scotland. 鈥淕lobal warming could
shift the balance,鈥� says White. Northern rabbits could become the victims of
their own enhanced reproductive success, his team says in a special issue of
Philosophic Transactions of the Royal Society B devoted to emerging
diseases (vol 356, p 1087).