Schmallenberg virus hits Europe again but should we be worried?

Lambs, don't worry. I's not all that bad.

I wrote back in February this year (2012) of a worrying outbreak of disease spreading across North-Western Europe, starting in Germany and ending up in the UK and even Spain and Italy.

The disease, manifesting itself in the Spring lambing/calving season, as fetal deformaties in these ruminants (also now alpacas). Many of which lead to the death of the newborn animal. It was quickly uncovered that this illness was caused by a previously unheard-of virus (an orthobunyavirus if you wanna know) now named after the town it was sampled from: Schmallenberg.

To date, no cases of human infection have been reported. And currently, cases have severely decreased as we leaving lambing/calving season.

Back seven months ago we really didn't know an awful lot about this emerging virus apart from that it looked not much like anything we had seen before. We didn't know how it got to Europe, we didn't know if it was going to stay here and we didn't know what to do about it. It was predicted that the virus was spread by midge flies living across Europe during the summer of 2011, the animals exhibiting a flu-like illness that barely registered with farmers. But when it came to the spring and the then newly pregnant sheep or cows gave birth, it soon became evident what damage the virus had done in this group of individuals.

What has happened since the Spring?

The months following this initial characterisation was a worrying one but scientifically really interesting:

I wrote in May that we had discovered where the virus had come from. A Japanese group had sequenced a load of new viruses that were cousins on Schmallenberg. One of the reasons we didn't know where the virus originated was due to really not knowing much about the genetic diversity of the orthobunyaviruses.

Bunyavirus - segmented genome. Is Schmallenberg composed of  segments from different viruses?

They then compared their sequences with the German isolate from back in early 2010. It became quickly obvious that parts of the viruses segmented genome came from different viruses and was hence a 'recombinant'. Recombining - or joining - together 3 fragments from two different kinds of viruses. But now with further increased sampling of orthobunyavirus genomes, Schmallenberg appears to be firmly rooted in one particular viral group while another virus cousin seems to be a recombinant.

A couple of months later, a Danish group showed that they could detect Schmallenberg virus RNA in one particular group of midges: Cullicoides obsoletos in Autumn 2011, when the virus was spreading across Europe, including Denmark.  

Culicoides sp. Reported vector for Schmallenberg virus.

Europe's stance downgraded but is it still here?

But Defra reported in June that the lack of seriousness of Schmallenberg virus had caused them to downgrade their view on the disease after only 0.002% of the susceptible ruminant population was affected. And those that were infected caused little negative impact to the farming.

SBV is no longer considered an emerging disease and therefore affected Member
States will no longer be reporting to the OIE on a regular basis. It was agreed at the
OIE 80th General Session that the disease is low impact with no public health risk
and negligible risk posed by commodities such as meat, milk, semen and embryos.

Thankfully European Food Safety Authority (EFSA) earmarked a 3 millions Euros for researchers to look into the biology of how Schmallenberg virus infects and causes disease in animals. Although nothing ear-marked for vaccine research. But despite this downgrading, the virus is in the news again when scientists at the UK Institute for Animal Health report (although there's no paper available) that they are still seeing new evidence of infection in cows in one of their farms when they look for antibodies.  The evidence has not been repeated in mainland Europe.

The UK guys take this as evidence that the virus survived the winter in the UK midges and is beginning to spread across the country. Although I'm not sure how much this could be explained by some animals mounting a slower response to the virus from the season before that. But maybe a year is too long for this.

Depending on midge dynamics across the country, which is itself dependent on weather and temperature etc (midges don't like the cold and the rain). The extent of the virus spreading and infecting new animals may be blocked by some animals having already mounted an immune response against it from last year and could be protected. You could  predict that this could drive the virus into areas that were not affected a year ago.

OK - it might be here, but calm down.

But as Defra and the EFSA stress, this virus poses no risk to humans and has only - to date - had a small  effect on European farming industry. It is no bluetongue disease however, I'm sure it's distressing for the individual farmers and it could have a relatively large effect on single farms that have been heavily affected. But in general,  even if this virus does return this summer (and we see its effects next Spring) hindsight has shown us that we shouldn't be as worried as we were 6 month ago.