A swine virus never been seen in North America and deadly to young pigs is spreading rapidly across the United States, and it is proving harder to control than previously believed.
The virus, with more than 100 positive cases, has spread to 13 states since it was diagnosed in the country last month, said Montserrat Torremorell, a specialist in swine health and professor at the University of Minnesota's College of Veterinary Medicine.
While the the virus has not tended to be fatal to older pigs, mortality among very young ones infected is commonly 50 percent and can be as high at 100 percent, according to veterinarians and other scientists studying the outbreak.
The strain of the virus, known as porcine epidemic diarrhea virus, that is making its way across the nation's hog farms and slaughterhouses is 99.4 percent similar in genetic structure to the PEDV that hit China's herds last year, the researchers say. First diagnosed in China in 2010, PEDV overran southern China and killed more than 1 million piglets, according to the Emerging Infectious Diseases journal of the Centers for Disease Control and Prevention.
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The virus does not pose any health risk to humans or other animals, and the meat from PEDV-infected pigs is safe for people to eat, according to federal officials and livestock economists.
No direct connection has been found between this outbreak and previous outbreaks in Asia and Europe, scientists said.
The U.S. pork industry had hoped the virus' spread would slow or at least plateau as the weather grew warm. But Tom Burkgren, executive director of the American Association of Swine Veterinarians, said PEDV has proved far more tolerant of heat than a more common malady, transmissible gastroenteritis.
PEDV was diagnosed earlier this month for the first time in Arkansas, Kansas and Pennsylvania. The virus had been found before that in barns in Colorado, Illinois, Indiana, Iowa, Michigan, Minnesota, Missouri, Ohio, Oklahoma and South Dakota.
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It has been found in baby pigs, adult sows and in other hogs being fattened for slaughter, said scientists investigating the outbreak. No known cases have been reported in Canada or Mexico.
When and how PEDV arrived in the United States remains a mystery. The total number of deaths from the outbreak is not known, and the uncertainty is fueling fears among traders, meat processors and farmers about the potential impact on pork supplies later in the year.
The outbreak comes as hog and wholesale pork prices in Iowa and Minnesota have surged to nearly two-year highs. Supermarkets are racing to fill meat cases for the summer grilling season as supplies tighten, analysts said. Hog supplies were already tight after last summer's historic drought drove up feed-grain costs, which prompted a higher-than-normal slaughter rate.
The first U.S. case of PEDV was reported May 17. But researchers at the National Veterinary Services Laboratory in Ames, Iowa, and other diagnostic labs have since discovered that PEDV arrived as early as April 16, according to the American Association of Swine Veterinarians. The labs have begun testing older samples taken from seemingly unrelated cases in an effort to track the virus' first appearance here.
Investigators with the Agriculture Department and others are hunting for clues to the widening outbreak and focusing on the nation's livestock transportation system.
PEDV most commonly is spread by pigs' ingesting contaminated feces. Investigators are focused on physical transmission, perhaps equipment marred with feces, or a person with dirty boots or dirty nails.
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"It could happen at the slaughterhouse, where you have a trailer unloading a truck of pigs that was positive," said Torremorell, who noted that diagnostic researchers at the University of Minnesota and elsewhere have tested hundreds of samples in recent weeks.
"If the person doesn't clean the trailer correctly, and then goes to load up another load of pigs that were negative for PEDV, that person could end up delivering a truck of pigs to an uninfected farm," she said.