|Still-born lamb after Schmallenberg infection. http://www.augsburger-allgemeine.de/i|
Europe is currently experiencing an incredibly worrying outbreak of disease across hundreds of farms in the North-West and it has finally popped up in the UK. The disease - caused by a previously unknown virus - has been causing a large number of still births in cows, goats and sheep after it was initially found in the Netherlands and Germany. What is worrying about this is our economic dependance on this kind of agriculture - but should we really be worried?
Following this initial outbreak in Germany/Netherlands it was rapidly discovered to be present in Belgium, France and the South-East of England where it was most likely spread by the movements of infected midge flies. And even now, Russia has begun to close off it's importing of Dutch meat and animals. The rest of the UK is even bracing itself for further spread of the virus and now the UK's veterinary labs have weighed in on the research. But a number of questions still need answered before we can really do anything about it, which is why so much interest has been generated over the last couple of weeks, especially as we have probably only seen the tip of the iceberg.
Named after the German town where it was initially found, Schmallenberg virus has been a cause for concern ever since it appeared during the end of last year. Looking back we can tell that it initially emerged into farm animals during last summer when Dutch and German farmers noticed that some of their animals (many of which would be pregnant) were coming down with a fever and having low yields of milk, although no deaths were noticed. Something was clearly not right and this set off alarm bells across the national labs in Europe but it was only going to get worse: as we came into lambing season the farmers started to notice the devastating effect of the virus on their farms.
After exhaustive tests for all the usual suspects, the German scientists were forced to get creative and using next generation sequencing technologies they were able to find the culprit: a new RNA virus called an orthobunyavirus. The only closest relatives were a group of viruses found across Asia known as the 'Simbu group' of viruses.
|Initial cases in Germany|
As the recent paper reports:
Members of this genus within the family Bunyaviridae are widely distributed in Asia, Africa, and Oceania; transmission occurs predominantly through biting midges, mainly Culicoides spp. and mosquitoes. Especially the Simbu serogroup, which includes Akabane, Aino, and Shamonda viruses, can play a role as pathogens of ruminants. However, to our knowledge, viruses of this serogroup have not previously been detected in Europe (6). Because of the origin of the first positive samples, the virus was provisionally named Schmallenberg virus.
Now we aren't completely sure how this virus is spread from one infected animal to another - or even how it moves between countries (infected flies or infected farm animals?) but as you can see above, we are basing this on how closely related viruses behave. However, it was predicted that if the virus was spread by midges it would most likely initially effect the South-East of England based on the patterns of wind dispersal - this turned out to be a correct prediction. Where these midges help to move the virus very efficiently during the summer, with the cold snap across Europe worsening it is unlikely that these insects would survive the winter. But the question whether the virus could survive the winter through the infected animals is to be seen - and this may not be true.
|A bunyavirus, from Overby et al (2007)|
The bunyaviruses are one of a couple of the groups of RNA viruses (negative sense RNA viruses to precise). They are spherical viruses (see above) whose genomes are shared across three chromosomes composed of RNA and protein (gold in the picture): they have a large (L) segment, a medium one (M) and a small one (S). This is much like influenza which has eight different genetic segments but the more parts a virus has the more worried we get: with this comes the chance for mixing up of the different genes which can result in very rapid evolution. These viruses are one of the most successful pathogens out there and a number of them even cause serious disease in humans. For example: Crimean-Congo hemorrhagic fever virus, spread by ticks, causes serious bleeding, respiratory problems and neurological dysfunction. And just in 2009, a Chinese group discovered that one of these viruses was the cause behind the deadly "Severe fever with thrombocytopenia syndrome".
The scientists stress that the risk of Schmallenberg to humans is minimal as none of the closely related bunyaviruses are able to infect us. But still they suggest that farmers and vets use appropriate hygiene measures when dealing with infected animals. Although, to date nobody has reported being infected but then nobody has looked so as we develop appropriate tests we may detect that many farmers have actually been infected.
|Virus movement from NW-Europe continent to UK. Where else will it appear?|
Because we are following this outbreak of disease in real-time we currently have very little information on how this is going to play out over the next couple of months,we do have a lot of speculation however. Of the important questions that need answered are: how come this virus is only appearing now? Where was it before this? How is the virus spread? Is it - as we suspect - by midges? And if so, what kind? How many animals have been infected by the virus? If we know this we can finally calculate how dangerous it actually is. Is it likely to spread further? When lambing season kicks into full swing are we going to see a huge rise in cases? And finally, is it worth it to develop a vaccine against it? Lets hope we can draw on some of our experiences with bluetongue virus, which bears an extreme similarity to this outbreak but occurred five years earlier.
If the virus does appear to be here to stay and we decide that a vaccine is the best thing to develop, lucky there is a research group in Scotland at the University of St Andrews that specializes in vaccines against bunyaviruses. But lets see how it plays out in the coming months: there's no point rushing head first into the unknown.Hoffmann, B., Scheuch, M., Höper, D., Jungblut, R., Holsteg, M., Schirrmeier, H., Eschbaumer, M., Goller, K., Wernike, K., Fischer, M., Breithaupt, A., Mettenleiter, T., & Beer, M. (2012). Novel Orthobunyavirus in Cattle, Europe, 2011 Emerging Infectious Diseases, 18 (3), 469-472 DOI: 10.3201/eid1803.111905
UPDATE with excellent articles on this topic for further reading:
My first news on the outbreak over at Wired from ScienceNow
UK Guardian article from the 23rd January covering the initial discovery of the virus in German/Dutch farms
Maryn McKenna of Superbug fame over at Wired blogs last week discussing the news of it's spread to the UK.