A veterinarian working with an Indiana farm has confirmed that Porcine Epidemic Diarrhoea, which has swept through pig herds in the United States, killing over 7 million pigs since it was first detected just over a year ago, can re-infect herds previously exposed to the disease.

The Indiana farm is the first to publicly confirm that it has suffered a second outbreak of the disease, which is thought to spread through exposure to faecal matter. Although Department of Agriculture officials in the US have insisted there is no threat to public health or food safety from the disease, there has been widespread criticism over authorities' handling of PEDv, including failure to introduce adequate biosecurity measures or make the virus notifiable when its rapid spread was first noticed.

Since the first outbreak in the United States, the disease has been reported in Canada, Mexico and Japan. Although PEDv is similar to viruses that have been seen before, notably one which affected animals in China in 2011, the current outbreak is thought to have originated in the US, though experts have been unable to explain its appearance.

The worrying revelation, from a farm whose owners wished to remain anonymous, and so arranged for their vet to speak on their behalf, may mean that PEDv is harder to contain than had initially been thought.  In the latest WASDE report, released earlier this month, USDA analysts were optimistic that PEDv could result in higher overall pork production in the States, though the death toll from the virus now amounts to over 10 percent of the US pig herd.

However, up until now, efforts to tackle the disease have worked on the assumption that, once infected, a pig will develop immunity to PEDv, though now it appears as though either this is not the case, or only limited immunity is developed. Although 'secondary outbreaks' had been rumoured for several months, none had been publicly confirmed until Tuesday.

Genetic sequencing from Indiana showed that the same strain of the virus had infected pigs at the farm in May 2013, then again in March this year. However, Indiana vet Matt Ackerman told news agency Reuters that piglets born to sows previously exposed to PEDv had a mortality rate of about 30 percent, compared to near total mortality in piglets during a first-time outbreak.  

USDA has embarked upon a vaccination programme and is recommending farmers and hauliers implement biosecurity measures, such as disinfecting trucks and facilities, though there is a strong belief in the industry that feed could be playing a part in transmission. In the US industry-backed research is looking into this possibility, though earlier research identified mothers' milk as the lone potential vector of feed-related transmission.

EU authorities have introduced stricter regulations on feed in response to the outbreak, though the EU Commission said it had been advised that conditions attached to the import of live pigs were already strict enough, and that there are currently no live imports planned from any of the affected regions.