SO BLUETONGUE virus is in northern Europe, perhaps to stay. While its arrival was predictable, the manner of its appearance was quite the opposite. It comes as a timely warning of the surprises that might be in store as global warming upsets the exquisite balance between Earth’s creatures.
Bluetongue is a virus of ruminants that is carried by biting flies called midges (or in some places, no-see-ums). It is resident in the tropics and in warm areas of North America and Australia, where livestock have mostly evolved resistance. Since 1998 it has crept north into Europe as the tropical midge that carries it has moved into new territory (see www.newscientist.com/article/dn12756).
The disease’s path precisely tracked the pattern of increasing night-time and winter temperatures. Europe’s livestock have no resistance, and as the midge moved through Italy, Iberia, southern France and the Balkans, bluetongue killed more than a million sheep.
Advertisement
ÐÓ°ÉÔ´´s warned in 2002 that northern European midges can carry bluetongue too, and might pick up where the southern midge left off. Then in 2006 the virus sprang a surprise: a South African strain, different from the viruses then creeping northwards, appeared in the Netherlands and spread rapidly across northern Europe. In August 2007 the same strain surfaced again: it had overwintered, though no one quite knows how. One idea is that it may lurk, ingeniously, in cows’ immune cells.
This was not a simple matter of a disease-carrying insect moving north but complicated nature adapting in complicated ways. Global warming had created conditions in northern Europe that allowed a one-off infection to explode. Midge species that normally do not carry bluetongue can do so when it gets warmer. They have temperature-sensitive genes. As the climate warms, the midges grow faster and have thinner gut walls, which the virus can penetrate. Warmer, wetter weather means more flies, while the virus replicates faster. A perfect combination for invasion.
There is more waiting in the wings. West Nile virus is affected by warming in similar ways to bluetongue, as are its relatives such as St Louis encephalitis virus and other insect-borne maladies such as chikungunya and Rift Valley fever, which has already moved out of Africa. African horse sickness can go wherever bluetongue goes. Farmers just beyond bluetongue’s reach in North America and Australia may be no safer than Europe was.
Who knows what other plagues of people, animals or crops will follow from global warming? We are about to find out.