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.
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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.
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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.
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"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.
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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."