Scientists have identified Reston ebolavirus—a member of the deadly Ebola group of hemorrhagic fever viruses—in domestic swine from the Philippines. Ebola is infamous for being highly contagious and causing death rates as high as 90 percent in some human outbreaks. This particular strain, first identified in monkeys in 1989 in a research laboratory in Reston, Va., is the only one of the family that is harmless to humans.

The outbreak in swine was discovered in July 2008 in the Philippines during an investigation of so-called blue ear disease in pigs, a respiratory condition that causes their ears to turn blue from lack of oxygen. Investigators there sent tissue and blood samples to Michael McIntosh of the U.S. Department of Agriculture at the Plum Island Animal Disease Center in Greenport, N.Y. McIntosh was surprised to find that the tissue samples also contained the Reston strain, which had not been previously identified in swine.

His team also confirmed pig-to-human Ebola transmission, identifying six pig handlers whose blood tested positive for antibodies to the virus. The individuals showed no symptoms, indicating that this strain is as harmless to humans now as it was in 1989. Authorities in Manila had announced preliminary findings in January, and McIntosh’s details appear in the July 10 Science.

McIntosh says there are still a lot of unknowns, including how the virus was transmitted to the pigs and whether they show any symptoms independent of blue ear disease. He worries that the virus’s passage through pigs could enable it to mutate into something more dangerous. The research also raises the possibility that pigs could become infected with lethal Ebola strains. “What is the level of risk? We really don’t know,” he says. “The fact that it shows up in domestic pigs raises that risk.”