Where Midges Fly
Hugh Pennington · Schmallenberg virus
Lambing is just starting. But the pictures on TV in the last few days have been of stillborns, and of newborns with bent legs, seized-up joints and crooked necks. Their mothers had been infected during pregnancy with the Schmallenberg virus, called after the German town where it was discovered last year. It belongs to a family – the bunyaviruses – that are mostly spread by insect bites.
A few bunyaviruses cause human diseases, such as Crimean-Congo haemorrhagic fever and Rift Valley fever. One group, the tospoviruses (the foundation member was tomato spotted wilt virus) infects plants and is spread by thrips. Schmallenberg is only very distantly related. Its genes are arranged in three RNA molecules; one has a sequence like that of Shimbu virus (first found in Nigeria), another a sequence from Aino virus (first isolated in Japan), and the third a sequence like that of Akabane virus (also discovered in Japan). Akabane causes abnormalities in calves and lambs, just like Schmallenberg. All three are harmless for humans. The hope and expectation is that Schmallenberg will be too.
Schmallenberg is a brand new combination of old mutated genes. It is causing a disease new to Europe. Its rapid discovery and description used state-of-the-art science. Last summer the Friedrich Loeffler Institute investigated dairy cows in North Rhine-Westphalia because of fever, loss of condition and poor milk yields. Blue tongue was suspected. But the tests were negative, as they were for other known viruses. So metagenomics was applied – the blind sequencing of whatever nucleic acids were there. Computer analysis of the results revealed the bunyavirus fingerprints. The virus has now been grown in the lab. A vaccine within two years is achievable.
On 5 January, before any cases had been reported in the UK, DEFRA published a map showing where infected midges, a reasonable guess as the likely vector, were most likely to have made landfall in England from Holland and Belgium, where the virus was well established, on the basis of Met Office models of wind patterns from July to November. The virus had arrived: deformed lambs were being born before the end of January – and most of the cases are where DEFRA said they would be, in Norfolk, Suffolk, Kent and East Sussex. But there have also been cases in Cornwall. Where next? Making predictions is difficult, particularly about the future, but midges love the west of Scotland.