Thursday, 30 August 2012

African Swine Fever on its way, (though not from Africa)

Sometimes I think the numbers quoted in the introductions to papers and presentations etc. are a little inflated. Certain strains of Bluetongue virus, such as BTV-8 (Europe) or BTV-17 (US) can result in a high case fatality of around 40%, and this is what's often quoted, but more usually the fatality rates are much much lower. H5N1 'bird 'flu' is certainly dangerous, but Vincent Racaniello recently highlighted that this might not necessarily be the whole story. There are though exceptions where the fatality rate is said to be high, and is high; African horse sickness, for example, never seems to be much less than 50% fatal, which is not great if you're a horse owner. African swine fever is another virus which fits into this latter 'always nasty' category. 

I've heard about the devastation caused by ASFV from a Ghanaian vet who said he had been to farms in Africa where every pig was dead. If you're a pig farmer you've got to be worried; sheep farmers losing lambs to Schmallenberg virus have had a hard time, but if 100% of your stock die, what then? Imagine a barn full of dead pigs, it can't be great.
Dead pigs as a result of African Swine Fever Virus

ASFV is a big DNA virus that's transmitted by soft ticks. In Africa the virus persists in the environment with its wild host, wart hogs. In Europe though, it has the option of persisting in wild boar, of which there are many.

ASFV has historically been linked, not surprisingly given the name, with sub-Saharan Africa. Before 1957 that's where it stayed. Since then there have been occasional introductions into Europe, and more or less has always been eradicated. That is, until 2007 when there was an outbreak of ASFV in Georgia. Since then the virus seems to have been hanging around in the region, with the odd report here and there of a new outbreak in the Caucasus. Now though, for the first time ever, it's in Ukraine. It's on the move and, rightly, people are worried. Thus far, the Middle East, where there aren't many pigs, has provided a buffer to ASFV encroachment into Europe through Turkey. Now though there is the possibility of the virus coming in via a different route into areas where the pig density is much greater.

In a forest near you: will AFSV-infected wild boar soon be roaming Europe?

Infected meat has always been a threat for ASFV introduction to the UK, although regulations and the restrictions on swill feeding help curtail this threat. However, wild boar don't respect international boundaries, so if the virus manages to get into the tick population, and then wild boar, it could result in a tricky situation where it's difficult to weed out the virus. Wild boar were recently at blame for an outbreak of Foot and Mouth Disease virus in Bulgaria, hopefully they won't be responsible for introducing ASFV.   

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