Image copyright Getty Images Image caption The virus has proved to be particularly deadly for young pigs

France is expected to suspend pig-related imports from a number of countries as worries grow over the spread of a deadly swine virus.

Porcine Epidemic Diarrhoea Virus (PEDv) has killed some seven million piglets in the US in the past year.

The disease has also been found in Canada, Mexico and Japan.

While the virus isn't harmful to humans or food, France is concerned over the potential economic impact and is set to suspend imports of live pigs and sperm.

PEDv is spread in faecal matter and attacks the guts of pigs, preventing them from absorbing liquids and nutrients.

Older animals can survive but fatality rates among piglets run between 80% and 100%.

So virulent is the agent that one expert estimated that a spoonful of infected manure would be enough to sicken the entire US herd.

The disease is believed to have its origins in China, according to the World Organisation for Animal Health (OIE).

"According to the information from genetic analyses, there is some similarity with a strain from Asia," director-general Dr Bernard Vallat told BBC News.

"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."

In North America, the disease has moved rapidly, with around 4,000 outbreaks in 30 US states, in four Canadian provinces and in parts of Mexico.

Virus on the move

Experts in the field believe that lax biosecurity is an important factor.

In June last year, a US study found that 17% of trucks going into a slaughterhouse were positive for the infection.

"They also discovered that 11% of the trucks that had been negative when they went into the slaughterhouse were subsequently positive when they left," said Dr Zoe Davies from the UK's National Pig Association (NPA).

"It's how many animals you are moving around, that's how its being spread."

Another factor that is making the disease more difficult to stop is the use of dried pig blood in feedstuffs that are given to weaned piglets.

Image copyright Getty Images Image caption China has seen a number of outbreaks of deadly pig diseases in recent years and it is believed that PEDv originated there

"The feed is suspected," said Dr Bernard Vallat from OIE.

"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," he said.

The French move to suspend the importing of live pigs, some by-products and pig sperm is being seen as a reaction to the lack of action at EU level.

In the UK, the NPA says it has already secured support from all major importers 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 the use of these feeds is more widely used in other EU countries, where movement of animals is also widespread.

There are concerns that if the virus was to gain a foothold in Europe it could lead to huge economic losses especially for breeders in Denmark, the Netherlands and Germany.

While the issue has been discussed by the EU Commission, there has been no agreement yet to restrict imports.

According to agency reports, French government officials say their suspension has been made while "waiting for a European decision".

PEDv was first diagnosed in the UK in 1971 but that strain was a milder form and pigs quickly adapted to it and became immune.

However the fact that European pigs have a history of exposure to a related virus may give some hope of protection, according to Dr Vallat.

"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."

This perspective though is challenged by Dr Zoe Davies who says that Europe is now highly vulnerable to the infection.

"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."

In the US, pig prices have risen considerably as a result of the losses to the virus while demand for pork shows no sign of abating. According to pig producers in the US, the industry is in for a strong financial year.

"One of the consequences of the problem, the restriction of the products in the market, mean perhaps prices could grow," said Dr Vallat.

"For the non-infected herds it is good news."

Follow Matt on Twitter @mattmcgrathbbc.