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.