There's increasing chat about the circulation of Schmallenberg virus in the UK this summer. Is that surprising? Maybe, it was more or less impossible to know as the virus was new. Likewise, new virus, new test. Serology (looking for antibodies as evidence that an animal has previously been infected) is the way to find where it's been and there's a commercial ELISA to do this serology. But how can you compare it to a gold standard when there isn't a gold standard? There's always the chance that the test doesn't detect as many as it should; the bTB skin test is the classic case of a test being hopeless.
|An ELISA showing cattle sera positive for SBV antibodies|
Is the circulation important? The worrying thing is that we only have a rough idea about prevalence. The situation is reminiscent of the situation in Germany in 2007; seeded with bluetongue virus in late 2006, BTV exploded in Germany the following summer, with 1000s farms being infected. The main indication of SBV infection seems to be congenital deformities, so, unlike BTV, we'll have to wait; it could still be the horror everyone was worried about.
Re-circulation does bring it onto the radar of vaccine companies though, so vaccines might be available soon, but when exactly nobody knows. One of the ideas with Akabane virus (one of SBV's close relatives) is that protection is achieved young and thus the animals may be more resistant to infection when pregnant.
So is Schmallenberg important? We still don't know. If it affects fertility it could be massive. Right now though it's 'watch this space'. Certainly in the south west of England, bTB remains the major scourge.