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.
(Read More: Sex Superbug Could Be 'Worse Than AIDS')
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.