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Concerns are spreading internationally over a particularly virulent strain of the porcine epidemic diarrhoea virus (PEDv). Thought to have originated in China, this strain of the virus is now suspected to have spread to herds in the USA, Canada, Mexico and Japan. Now BBC News reports that France is planning to stop pig-related imports from infected countries, including live pigs, some by-products and pig sperm. The French action is thought to be a reaction to the perceived lack of decisive action on behalf of the European Union. Agency reports state that French government officials say their suspension has been made while "waiting for a European decision".

Porcine epidemic diarrhoea is an enteric disease of pigs caused by infection with a virus which is a member of the Coronaviridae family. It causes acute diarrhoea and dehydration in pigs. The disease is not, however, harmful to humans. Porcine epidemic diarrhoea was first observed in 1971 in English fattening pigs and subsequently spread around Europe. This PEDv type I strain was less virulent than the strain currently causing concern and pigs developed immunity to it. Other strains have since evolved and the disease has become problematic in many parts of the world, notably in Asian countries where severe outbreaks have affected new-born pig mortality rates.

Older pigs can survive PEDv infections but piglets are highly susceptible to the strain that is currently causing concern, with a 80% and 100% mortality rate. While it is not yet certain that the same strain has spread from Asia to the US, this is suspected to be the case. Dr Bernard Vallat, Director-General of the World Organisation for Animal Health (OIE), says: "According to the information from genetic analyses, there is some similarity with a strain from Asia…But the evidence of the crossing from Asia to the US is not yet established. For the moment it is not possible to make a final conclusion on the formal link, it is a suspicion."

PEDv is spread via faecal matter. Lax biosecurity is suspected to be a factor in the spread of the disease, according to BBC News. For example, a US study carried out in June last year showed that 17% of trucks going into a slaughterhouse were positive for the PEDV infection. According to Dr Zoe Davis of the UK's National Pig Association (NPA): "They also discovered that 11% of the trucks that had been negative when they went into the slaughterhouse were subsequently positive when they left…It's how many animals you are moving around, that's how it’s being spread."

It is also suspected that the practice of using dried pig blood in feedstuffs for weaned piglets is contributing to the problem. Dr Bernard Vallat explains: "The feed is suspected…Blood from slaughterhouses with insufficient heat treatment is suspected to be the origin. We don't have a scientific publication on that but it is highly suspected.” However, Dr Vallat believes that the history of exposure of European pigs to PEDv may confer some immunity: "It circulated before in Europe but it was a different strain. If there is some remaining circulating virus there is a possibility that animals would be protected - but it is not sure." Dr Zoe Davis disagrees with this optimistic assessment: "Everyone seems to think that because we've had versions of PEDv in the past we will have some immunity to this new strain and we know categorically that this is not the case…We've tested our own herds and we think around 10% of the animals have antibodies to the older strains, we are effectively a naive herd, which is why we are worried."

The potentially devastating consequences of the disease are evident in the US where 7 million piglets have been killed in the last year due to PEDv infection. In the UK, the NPA claims that all major importers support moves to restrict pigs from infected countries. It says that more than 92% of pigs reared in the UK are not fed on blood products. However, in other EU countries these types of foodstuffs are more common and there is also widespread movement of animals. This increases the risk of the virus becoming established in Europe, with potentially devastating economic consequences for major pig-breeding countries including the Netherlands, Germany and Denmark. The EU has not decided yet on any move to restrict imports. This is thought to have contributed to the French unilateral decision on import restriction and to the thinking in countries such as the UK.

Another consequence of this outbreak is that the price of pork is likely to rise. Already the US has experienced an increase in pig prices due to the virally-induced piglet losses. Dr Vallat says: "One of the consequences of the problem, the restriction of the products in the market, mean perhaps prices could grow…For the non-infected herds it is good news."

Sources:

http://www.bbc.com/news/science-environment-27256466 [Accessed 9 May 2014].

https://www.avma.org/News/JAVMANews/Pages/130901x.aspx[Accessed 9 May 2014].

Song, D. & Park, B. 2012, "Porcine epidemic diarrhoea virus: a comprehensive review of molecular epidemiology, diagnosis, and vaccines", Virus genes, vol. 44, no. 2, pp. 167-175.