(Adds USDA comment in paragraphs 6-7)
By Tom Polansek
CHICAGO, May 28 (Reuters) - An Indiana farm has become the first to confirm publicly it suffered a second outbreak of a deadly pig virus, fueling concerns that a disease that has wiped out 10 percent of the U.S. hog population will be harder to contain than producers and veterinarians expected.
The farm, through its veterinarian, publicly acknowledged on Tuesday a repeat incident of Porcine Epidemic Diarrhea virus (PEDv), which has killed up to 7 million pigs and pushed pork prices to record highs since it was first identified in the United States a year ago.
Matt Ackerman, whose veterinary practice is in southeastern Indiana, told Reuters the farm's operators did not want to be identified but authorized him to speak on their behalf.
The state and federal effort to stamp out PEDv has operated on an assumption that a pig, once infected, develops immunity and will not be afflicted by the disease again for at least several years. Likewise, farms that had endured the disease were not known to suffer secondary outbreaks.
But a year after the virus was identified, repeat outbreaks have occurred at farms but not been publicly confirmed before now. These so-called secondary outbreaks are a challenge to efforts to stem the disease, which is almost always fatal to baby piglets.
The U.S. Department of Agriculture is fighting against repeated outbreaks by trying to extend immunity in female hogs through effective vaccines, Chief Veterinary Officer John Clifford told Reuters at the general session of the World Animal Health Organization in Paris.
"It happens and it could happen again," he said about secondary outbreaks of PEDv. "We need to practice good bio-security, cleaning and disinfection, all-in all-out, in order to break the cycle and prevent its re-emergence."
Nationwide, PEDv outbreaks seem to recur in about 30 percent of infected farms, the American Association of Swine Veterinarians told Reuters, confirming for the first time the likelihood of repeated outbreaks.
Hog futures reached a record high last month and are up nearly 25 percent at $113.75 per hundredweight since the first U.S. outbreak was confirmed last year. Retail pork prices also have set new records, and a wave of re-infection could cause even more losses to the nation's hog herd.
In the Indiana case, genetic sequencing showed the "exact same strain" of PEDv hit pigs at the farm in May 2013 and again in March 2014, said Ackerman, who collected samples from the farm.
Piglets born to sows that were infected for a second time have a death rate of about 30 percent, compared to near-total death loss among newborn piglets during the first outbreak, he said.
The incidence of the disease "re-breaking" on farms after it appeared to have been wiped out, indicates that the risk for ongoing severe losses from the virus is bigger than previously expected. The lack of long-term immunity also means hog producers must keep up strict bio-security measures to fight the disease, which has already spread to 30 states.
The virus does not pose a risk to human health and is not a food safety issue, according to the USDA.
REASONS FOR RE-INFECTION UNCLEAR
Veterinarians and others have been unable to predict the duration of immunity to PEDv in hogs following exposure, in part because the disease had never been in the United States before last year.
Ackerman had thought hogs would have a natural immunity to PEDv for three years after being infected because that is the case for a similar disease called Transmissible Gastroenteritis.
"Just because a farm broke with PEDv last year doesn't mean that they are protected from re-breaking with it this year," he said in a telephone interview.
Ackerman said he did not know why the female pigs, or sows, on the Indiana farm were re-infected after being exposed to the virus during the original outbreak last year. At the time, they were about six months to a year old. The sows are having piglets and passing limited immunity on to their offspring, he said.
The farm "does an excellent job of sanitation," he said. "That's why it's so hard to figure out why they're struggling with it."
The repeat case of PEDv in Indiana puts to rest gossip about a re-break in the state that has passed from one Midwest farmer to another for weeks. Producers are on edge because no vaccine has yet been able to completely protect pigs from the disease.
PEDv is transmitted from pig to pig by contact with pig manure, which contains the virus. It can be transmitted from farm to farm on trucks, and many veterinarians also believe it is spreading through animal feed.
Harry Snelson, a veterinarian who represents the American Association of Swine Veterinarians, said repeat occurrences tend not to be as severe as the first outbreak, although farms are still losing pigs.
One potential reason for repeat outbreaks is that high levels of the virus, found in fecal material, overwhelm hogs' natural immunity, Snelson said.
"It probably doesn't take a whole lot to override the level of immunity that we're getting," he said. "Obviously immunity is a key part of our being able to control the spread of the virus."
Preliminary results from studies on immunity, directed by the National Pork Board, confirm "immunity does appear not to be very long lived," said Lisa Becton, director of swine health information for the board. The board has collected more than $2 million for research on PEDv.
The re-breaking is causing concern among farmers and meat packers across the country, as the PEDv outbreak continues to spread with no definitive solution in sight.
"If you have that disease, it causes a huge death loss, and then you get it again," said Josh Trenary, executive director of Indiana Pork. "It's pretty clear why it would be concerning." (Additional reporting by Sybille de La Hamaide in Paris; Editing by Cynthia Osterman and Grant McCool)